Biomechanical analysis of plate systems for proximal humerus fractures: a systematic literature review
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paper_title: A BIOMECHANICAL COMPARISON OF LOCKING PLATE AND LOCKING NAIL IMPLANTS USED FOR FRACTURES OF THE PROXIMAL HUMERUS.

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The aim of this study was to determine the biomechanical behavior of two different implants used in the fixation of proximal humerus fractures. The two implants in this study are specifically designed for the fixation of proximal humerus fractures and both utilize the concept of fixed angle locking screws. Bone densitometry was performed prior to fracture production and fixation. A reproducible three-part fracture was created in paired human cadaveric bone and then fixed using the locking screw implants. Stress/strain curves for the bone-implant construct were created for loads applied in cantilever bending and torsion to determine the relative stiffness below the yield point. Following this each construct was tested to failure with a valgus bending load. The locking nail implant provided a significantly stiffer construct in torsion, valgus, extension and flexion at loads below failure threshold. The valgus load to failure was significantly higher for the nail. The mode of failure was different between implants.
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paper_title: Internal fixation of proximal humerus fractures using the locking proximal humerus plate.

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OBJECTIVE ::: Stable fixation of unstable proximal humerus fractures until bony consolidation. Early mobilization of the shoulder and early active rehabilitation program to ensure a good functional outcome and a good restoration of the activities of daily living. ::: ::: ::: INDICATIONS ::: Unstable two-, three- and four-part fractures of the proximal humerus (classified according to the AO classification as: 11-A2, A3, B1, B2, B3, C1, C2, C3). Nonunions of the proximal humerus, especially at the neck. Pathologic fractures of the proximal humerus. ::: ::: ::: CONTRAINDICATIONS ::: Comminuted humeral head fractures in old patients, which cannot be reconstructed adequately. Proximal humerus fractures in the immature patient. Local infection after previous surgery. ::: ::: ::: SURGICAL TECHNIQUE ::: Deltopectoral approach. Blunt mobilization of the deltoid muscle. Suture loops through the supraspinatus tendon, the infraspinatus tendon, and the subscapularis tendon close to their bony insertion. Careful indirect reduction of the fracture fragments without further damage to their blood supply. Correct positioning of the LPHP (Locking Proximal Humerus Plate) on the lateral side of the humerus, approximately 5 mm below the tip of the greater tuberosity. Indirect approximation of the subcapital fracture component to the plate, by tightening a standard 3.5-mm cortical bone screw inserted into the first hole distal to the metaphyseal fracture line. Temporary fixation of the plate with 1.8-mm Kirschner wires. Fixed-angle fixation of the plate to the bone, using locking screws. Additional stabilization of the tuberosities to the plate with suture loops. ::: ::: ::: RESULTS ::: Between January 1, 1997 and April 30, 2002, 64 patients with acute fractures of the proximal humerus were treated with fixed-angle plating at the UKH Graz. 36 patients meeting the inclusion criteria (that is primary operative stabilization within 14 days after trauma in a standardized way and minimal follow-up period of 12 months) were assessed 31 months after surgery on average, using the Constant Score and the DASH Score. The mean age of the 22 women and 14 men was 57.5 years (21-78 years). According to the AO classification eight fractures were classified as 11-A3, one fracture as B1, five fractures as B2, three fractures as B3, one fracture as C1, 16 fractures as C2, and two fractures as C3. A mean Constant Score of 62.6 points and an age-related Constant Score of 80.7% on average, as well as a DASH Score of 18.0 points were obtained, constituting a satisfactory result in three quarters of all patients. Complications observed were two humeral head necroses, one partial necrosis after a head-splitting fracture with nevertheless good clinical result, and a deep infection in two cases. Breakage of the plate was seen in one patient with an A3.3 fracture without medial buttress; no further surgery was necessary; the fracture healed after a short period of immobilization.
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paper_title: Basic Epidemiology of Fractures of the Upper and Lower Limb among Americans over 65 Years of Age

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Current knowledge regarding the basic epidemiology of fractures is largely limited to a few fracture sites, notably those of the hip and distal forearm. To clarify the patterns of incidence of limb fractures in the elderly, we used data from a 5% sample of the U.S. Medicare population over age 65 years during the years 1986-1990. We identified incident fractures of the proximal humerus, other parts of the humerus, proximal radius/ ulna, shaft of the radius/ulna, distal radius/ulna, pelvis, hip, other parts of the femur, patella, ankle, and other parts of the tibia/fibula from diagnoses and procedures coded on claims for inpatient services, outpatient facility use, and physician services. We used Poisson regression to investigate the relation between demographic factors and fracture risk at these sites. Fractures at the hip were the most common, accounting for 38% of the fractures identified. The proximal humerus, distal radius/ulna, and ankle also were common fracture sites. A pattern of rapidly rising rates with age was seen for fractures of the pelvis, hip, and other parts of the femur among women. Fractures distal to the elbow or knee, however, had, at most, modest increases in incidence with age over 65 years. For each of the fractures studied, women had higher rates than men of the same race, and whites generally had higher rates than blacks of the same gender. Gender-related differences in risk were larger among whites than among blacks, and racial differences in risk were more marked among women than among men.
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paper_title: Internal fixation of unstable proximal humerus fractures with an anatomically preshaped interlocking plate: a clinical and radiologic evaluation.

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BACKGROUND ::: We evaluated the outcome after internal fixation of unstable or displaced proximal humerus fractures with a new fixed-angle implant. ::: ::: ::: METHODS ::: Prospective consecutive study with a 1-year clinical follow-up in 119 of 137 patients (87%; mean 68 +/- 15 years; 31 two-, 47 three-, and 41 four-part fractures). ::: ::: ::: RESULTS ::: One year postoperatively, the range of motion of the injured side demonstrated on average four-fifths of the function of the contralateral side. Ninety-five percentage of patients (n = 114) could dress themselves independently with no or only slight restriction. The mean disabilities of the arm, shoulder, and hand score was 21 (range, 0-62). The absolute and relative Constant score significantly (p < 0.001) improved from 56 +/- 18 (75% +/- 21%) at 6 months postoperatively to up to 65 +/- 18 (82% +/- 18%) at 12 months postoperatively. The initial fracture configuration did not have a significant influence on clinical outcome or complications. Twenty-six patients (22%) underwent a reintervention because of a clinical problem or subjective complaint, which led to total or relevant relief of problems in 23 patients (87%). Radiologic follow-up revealed a significant correction of the mean fragment angles (p < 0.001) postoperatively compared with initial postcrash radiographs. The precision of intraoperative reduction had a significant impact on the patient's disabilities of the arm, shoulder, and hand scoring (p = 0.02). A comparison of the last evaluable radiographs with the intraoperative intensifier images revealed a mean loss of reduction over time of </=2 degrees. ::: ::: ::: CONCLUSIONS ::: The angular stability of the fixed-angle interlocking plate could be proven radiologically in this clinical series. This fixation system seems to be a promising alternative in the treatment of displaced or unstable proximal humerus fractures. Clinical outcome can be further improved by avoiding certain minor errors in operative technique.
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paper_title: Proximal humerus fractures: a comparative biomechanical analysis of intra and extramedullary implants

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INTRODUCTION ::: The biomechanical stability of a newly developed humerus nail (Sirustrade mark) for the treatment of fractures of the proximal humerus was analyzed in comparison to established systems. In total, three randomized groups were formed (n = 4 pairs) from 12 matched pairs of human cadaver humeri. ::: ::: ::: MATERIALS AND METHODS ::: All intact bones were mechanically characterized by five subsequent load cycles under bending and torsional loading. The bending moment at the osteotomy was 7.5 N m the torsional moment was 8.3 N m over the hole specimen length. Loading was consistently initiated at the distal epiphysis and the deformation at the distal epiphysis was continuously recorded. Prior to implant reinforcement, a defect of 5 mm was created to simulate an unstable subcapital humerus fracture. For paired comparison, one humerus of each pair was stabilized with the Sirus proximal humerus nail while the counterpart was stabilized by a reference implant. In detail, the following groups were created: Sirus versus Proximal humerus nail (PHN) with spiral blade (group I); Sirus versus PHILOS plate (group II); Sirus versus 4.5 mm AO T-plate (group III). ::: ::: ::: RESULTS ::: The Sirus nail demonstrated significantly higher stiffness values compared to the reference implants for both bending and torsional loading. The following distal epiphyseal displacements were recorded for a bending moment of 7.5 N m at the osteotomy: Sirus I: 8.8 mm, II: 8.4 mm, III: 7.7 mm (range 6.9-10.9), PHN 21.1 mm (range 15.7-25.2) (P = 0.005), PHILOS plate 27.5 mm (range 21.6-35.8) (P < 0.001), 4.5 AO T-plate 26.3 mm (range 24.3-33.9) (P = 0.01). The rotations corresponding to 8.3 N m torsional moment were: Sirus I: 9.1 degrees , II: 9.3 degrees , III: 10.6 degrees (range 7.5-12.2), PHN 13.5 degrees (range 10.3-15.6) (P = 0.158), PHILOS plate 15.6 degrees (range 13.7-20.8) (P = 0.007), 4.5 AO T-Platte 14.1 degrees (range 11.5-19.7) (P = 0.158). ::: ::: ::: CONCLUSION ::: The intramedullary load carriers were biomechanically superior when compared to the plating systems in the fracture model presented here. Supplementary, the Sirus Nail showed higher stiffness values than the PHN. However, the latter are gaining in importance due to the possibility of minimal invasive implantation. Whether this will be associated with functional advantages requires further clinical investigation.
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paper_title: Fixation of proximal humeral fractures with the Polarus nail.

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Thirty patients with fractures of the proximal humerus were treated by internal fixation with an intramedullary locked nail. Fourteen of these patients were more than 60 years of age; 23 patients had 2-part fractures (surgical neck fractures) and were operated on within an average of 3 days after injury. At follow-up, 20 (80%) of 25 patients showed satisfactory to excellent functional outcomes, as measured by Constant score. All but 1 fracture progressed to clinical and radiologic union. The good functional results indicate that the Polarus nail is a satisfactory mechanical device that can be used in the treatment of displaced proximal humeral fractures in both the young and the elderly with osteopenic bone.
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paper_title: Open reduction and internal fixation of three- and four-part fractures of the proximal humerus.

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Thirty-one patients, ranging in age from 19 to 62 years (average, 55 years), were evaluated an average of six years seven months (range, one to 12 years) after open reduction and internal fixation of a three- or four-part fracture of the proximal humerus. Six patients had an associated dislocation of the humeral head. A modified cloverleaf plate was used in 26 cases and an AO T-plate in five cases. All fractures healed. No avascular necrosis of the humeral head was observed at follow-up examination. Twenty-three patients had an excellent result, two had a good result, and six had a fair result. Open reduction and internal fixation of three- and four-part fractures of the proximal humerus are indicated as initial treatment, even before the use of a prosthetic replacement, which should be recommended only for elderly patients with osteoporotic bones.
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paper_title: Internal fixation of proximal humeral fractures with a Polarus humeral nail

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BackgroundProximal humeral fractures occur frequently. Displaced or unstable fractures require open reduction and internal fixation. Our objective was to investigate the clinical and radiographic results of the internal fixation using Polarus humeral nails for fractures of the proximal humerus.Materials and methodsFrom January 2001 to April 2006, 54 shoulders of 54 patients (44 females, 10 males) underwent the intramedullary fixation using Polarus humeral nail. Mean age of the patients was 66-year-old (39–89) at the time of the surgery. Fracture-type by Neer classification was 2-part (29 shoulders), 3-part (22 shoulders) and 4-part (3 shoulders). The clinical and radiological outcomes were evaluated.ResultsAll the shoulders after osteosynthesis obtained bone-union. There was no osteonecrosis of the humeral head. Functional outcome measured by JOA score averaged 81 points. Totally 43 patients (79%) had satisfactory to excellent results. Varus deformity was seen in 4 shoulders (8%) and the deformity of the greater tuberosity in 4 (8%).ConclusionThe Polarus intramedullary humeral nail is effective for the treatment of proximal humeral fractures.
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paper_title: Angular and sliding stable antegrade nailing (Targon PH) for the treatment of proximal humeral fractures

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INTRODUCTION ::: The optimal surgical treatment for displaced proximal humeral fractures continues to be controversial. Different treatment modalities are available. Mechanical implant-related problems, however, and the preservation of the biological integrity of the humeral head remain unsolved. New implants providing angular stability are expected to maintain the intraoperative result of reduction until definitive healing. The purpose of this study was to evaluate the functional outcome and the complication rate of an angular and sliding stable antegrade interlocking nail for the treatment of displaced proximal humeral fractures. ::: ::: ::: MATERIALS AND METHODS ::: In a prospective study, 112 consecutive patients with displaced proximal humeral fractures were treated. Complete 12 months postoperative follow-up was available for 74 patients. Fracture types were classified according to the Neer-classification. Clinical, functional and radiographic follow-up evaluations were performed 3, 6 and 12 months after surgery. The Constant Score (CS) was used to assess shoulder function. ::: ::: ::: RESULTS ::: All fractures were united. The CS (MV +/- SD) of the injured side 3, 6 and 12 months after surgery were 42.1 +/- 15.1, 56.1 +/- 20.1 and 70.9 +/- 19.3, respectively. Patients sustaining Neer III and VI/3 fractures revealed better shoulder function (68.8 +/- 14.7, 74.9 +/- 17.6) 12 months postoperatively than those with Neer IV/4 fractures (60.7 +/- 23.2), where most complications occurred. Complications requiring surgical therapy were seen in a total of 24 patients (30%) and included backing out of screws in nails without peak inlay (20%; 2000-2003), protrusion of screws into the gleno-humeral joint (5%), loss of reduction with malunion (9%) and major tubercle displacement (7%). ::: ::: ::: CONCLUSION ::: The treatment of displaced proximal humeral fractures with an angular and sliding stable antegrade nail (Targon-PH) led to good functional results, especially in 2- and 3-part fractures. There exists a substantial risk for postoperative complications and bad motor function in Neer IV/4 fractures. Lateral backing out of screws was abolished by implant modifications (PEEK-inlay) from 2003 onwards. Additional tension wire banding of the major tubercle may further reduce the risk of secondary displacement.
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paper_title: Treatment of proximal humeral fractures with Polarus nail fixation.

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Abstract A chart review of 20 patients who sustained acute proximal humeral fractures and who were treated by surgical stabilization with locked antegrade humeral intramedullary nails (Polarus nails) was undertaken. The clinical outcome measurements were fracture healing, infection, and neurologic injury. Radiologic outcome measurements included fracture alignment, loosening, fixation and hardware failure, and malunion and nonunion. Of 20 fractures, 11 healed without complications. The mean immediate postoperative and final radiographic valgus neck/shaft angulation measured 131°. Of the 20 implants, 3 had proximal fixation screw loosening. Of the 20 implants, 2 underwent revision surgery for proximal fixation failure. With certain fracture types, the Polarus intramedullary humeral nail can be an effective implant. In fracture cases involving an unstable or comminuted lateral metaphyseal fracture, if the starting point extends into the greater tuberosity, fixation failure or fracture displacement may result.
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paper_title: Fixation of proximal humerus fractures using the PHILOS plate: early experience.

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UNLABELLED ::: Proximal humeral fractures, especially in elderly patients, remain a challenging problem for the surgeon because the complication rate for these fractures still remains high. The internal locked system (PHILOS) plate is a new device used for proximal humerus fracture fixation is designed to decrease the high complication rate. We prospectively evaluated our early experience using this system. Twenty patients with fractures of the proximal humerus were treated with a PHILOS plate from September 2001 to January 2004 at Princess Alexandra Hospital in Harlow, UK. Functional assessment was done using the Constant shoulder score. Two patients who had brachial plexus injury were evaluated only with the visual analogue score because we thought that the Constant objective assessment would be unreliable. Complications were monitored. The mean Constant score was found to be 76.1% (range, 30-100%). The preliminary results seem to be satisfactory. According to our experience, the plate design provides stable fixation with a good functional outcome and eliminates most hardware problems such as failure and impingement syndrome. The PHILOS plate is suitable for the majority of fractures providing that the correct surgical technique is used. ::: ::: ::: LEVEL OF EVIDENCE ::: Therapeutic study, level IV (case series). See the Guidelines for Authors for a complete description of levels of evidence.
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paper_title: Early complications in proximal humerus fractures (OTA Types 11) treated with locked plates.

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Purpose:To examine our incidence of early complications that occur using the Proximal Humeral Internal Locking System (PHILOS) and to determine the contributing factors.Setting:Academic medical center.Patients:Fifty-one consecutive patients treated with a proximal humerus locking plate.Outcome:Devel
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paper_title: Surgical neck fractures of the proximal humerus : a laboratory evaluation of ten fixation techniques

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Objective : A biomechanical cadaver study was performed to compare the stability and ultimate strength of ten standard fixation techniques used for the treatment of surgical neck fractures of the proximal humerus. Design : One hundred twenty (60 fresh frozen, 60 embalmed) proximal humerus specimens were selected and divided into two groups : fresh frozen specimens represented a nonosteopenic group and embalmed specimens an osteopenic group. Simulated fractures were created at the level of the surgical neck, reduced, and randomly assigned to one of ten methods of fixation (six fresh frozen and six embalmed specimens per fixation group). These constructs were then mechanically tested with the humeri oriented to create primarily shear loading of the fixation. Results and Conclusions : The T-plate and screws provided significantly stronger fixation (p < 0.005) in the fresh frozen specimens than all other methods. The Ender nails/tension band construct was the second strongest fixation technique, providing significantly stronger fixation (p < 0.01) than all the remaining techniques. Four Schanz pins with one pin placed through the greater tuberosity followed by the T-plate and screws provided the strongest fixation in embalmed specimens. Tension band fixation in both humeral groups was shown to provide the least effective fixation.
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paper_title: New trends in the treatment of proximal humerus fractures.

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UNLABELLED ::: For complex proximal humeral fractures, most authors agree on the importance of anatomic reduction and stable fixation to allow early range of motion. Currently a variety of techniques are used such as K-wires, t-plates, and primary prosthesis among others. However, no current treatment guidelines have been established. Newer implants provide greater angular stability, better biomechanical properties, and enhanced anchorage in these complex injuries. These implants therefore have a potential for achieving better results in treating complex fractures. We discuss current treatment concepts and focus on biomechanics and early results of new implants designed to provide angular stability. ::: ::: ::: LEVEL OF EVIDENCE ::: Expert Opinion, Level V. See the Guidelines for Authors for a complete description of levels of evidence.
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paper_title: Avascular necrosis in proximal humeral fractures in patients treated with operative fixation: a meta-analysis

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Proximal humeral fractures are common lesions of the elderly, but there are no established treatment guidelines. A surgical treatment for comminuted and displaced fractures of the proximal humerus was developed and is still evolving. The aim of this study was to perform a quantitative review to evaluate the risk of avascular necrosis (AVN) in patients with proximal humeral fractures who were treated by operative fixation compared with conservative treatment. We searched the PubMed, MEDLINE, Springer, Elsevier Science Direct, Cochrane Library, Google Scholar, China National Knowledge Infrastructure (in Chinese), and Wanfang database (in Chinese) up to December 2013 to identify studies related to operative fixation and AVN in patients with proximal humeral fractures. Seven studies with a total of 291 patients (142 operative fixation cases and 149 conservative treatment cases) with proximal humeral fractures were considered in the meta-analysis. The overall meta-analysis showed no significant difference in the incidence of AVN between the two groups [odds ratio (OR) 1.42, 95% confidence interval (CI) 0.33–6.11, p = 0.64]. The subgroup meta-analysis by study design (retrospective/prospective), sample size (≤40/>40), and ethnicity (European/Asian) demonstrated similar results. However, the subgroup analysis by specific operative approach (plate fixation/tension band wiring fixation/others) indicated that plate fixation was associated with a higher rate of AVN than conservative treatment (OR 0.20, 95% CI 0.05–0.76, p = 0.019). Plate fixation was associated with a higher risk of AVN development than conservative treatment in patients with proximal humeral fractures.
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paper_title: Biomechanical evaluation of locked plating in proximal humeral fractures

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The ideal method of fixation in proximal humeral fractures is not well established. Locked plating is a potential solution, but to date, there has been little support shown in the literature. We compared the biomechanical performance of a locked plate with that of an intramedullary humeral nail in a cadaveric model. Paired fresh-frozen cadaveric humeri (N = 5) were instrumented with either a locked plate or an intramedullary nail after creation of a 3-part osteotomy. Construct stiffness, cyclic loading behavior, and load to failure were evaluated. The locked plate was more stiff in valgus loading than the nail (P = .003). All other loading vectors showed no statistical differences in stiffness between the two constructs. The load to failure was 828 N for the plate and 901 N for the nail. The nail showed interfragmentary motion (degrees), or toggle, at zero load, whereas the plate did not. The locked plate, being stable at zero load, may prove useful in earlier pain-free rehabilitation of proximal humeral fractures.
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paper_title: Surgical treatment of two-part fractures of the proximal humerus: comparison of fixed-angle plate osteosynthesis and Zifko nails.

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INTRODUCTION ::: Closed reduction and percutaneous pinning using Zifko nails offer the advantage of a minimal soft-tissue dissection but have been criticised for limited stability and secondary fracture dislocation. Angular stable plate osteosynthesis enables anatomic reduction, but carries the risk of soft tissue traumatisation and consecutive humeral head necrosis. The present study compares the clinical and radiological outcome of patients with dislocated two-part fractures of the proximal humerus, who were treated with either Zifko nails or angular stable plate fixation. ::: ::: ::: MATERIAL AND METHODS ::: A matched-pair analysis was performed and patient groups were matched according to age (3 years), sex and fracture type. As many as 11 pairs of patients with a minimum follow-up of 3 years were formed and investigated radiographically and clinically using the Constant score (CS) and the visual analogue scale (VAS) for the patients' satisfaction. ::: ::: ::: RESULTS ::: At the time of follow-up, the absolute CS was 83 points in the PHP group and 78 points in the Zifko group (n.s.). Neither in the age and gender-corrected CS was found a significant difference between the study groups (PHP 104 29, Zifko 95 17, n.s.) nor in terms of subjective patient satisfaction (PHP 6.54; Zifko 7.8, n.s.). The complication rate was also comparable in both groups. ::: ::: ::: CONCLUSION ::: In conclusion, Zifko nailing represents a cost-effective minimally invasive surgical method with a complication rate and clinical outcome comparable to that after angular stable osteosynthesis by angular stable plate fixation in the treatment of two-part fractures of the proximal humerus.
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paper_title: Displacement/Screw Cutout After Open Reduction and Locked Plate Fixation of Humeral Fractures

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Background: Fixation of proximal humeral fractures is challenging. Locking plate technology offers mechanical advantages for treating unstable fractures in weak bone. In this study, we assessed the radiographic and clinical results of a single surgeon's experience treating proximal humeral fractures with a locked proximal humeral plate. ::: ::: Methods: Fifty-three adult patients with a displaced proximal humeral fracture were treated with a proximal humeral locking plate over a forty-five-month period. A standard postoperative rehabilitation regimen was followed. Radiographs were made at two weeks, six weeks, three months, six months, and one year and were examined for fracture alignment, fracture displacement, hardware position, and healing. Postoperative outcomes were collected with questionnaires. ::: ::: Results: Fifty-two (98%) of the fifty-three fractures healed by six months. Nineteen patients (36%) had radiographic signs of a complication, including screw cutout with intra-articular displacement in twelve (23%), substantial (>10°) varus displacement in thirteen (25%), and osteonecrosis in two (4%). These radiographic signs of a complication occurred in twelve (57%) of twenty-one patients older than sixty years of age and in seven (22%) of thirty-two patients under sixty years of age (p = 0.0015). Screw cutout occurred in nine (43%) of the twenty-one patients older than sixty years. Patients with a complication had worse functional outcomes as measured with the Short Musculoskeletal Function Assessment (p < 0.05) and the Quick Disabilities of the Arm, Shoulder and Hand (p < 0.001) questionnaires. We were unable to demonstrate a relationship between fracture type and complications. Revision surgery was performed in seven (13%) of the fifty-three patients. There were no cases of infection, nerve injury, or hardware failure. ::: ::: Conclusions: The use of locking plates in the surgical treatment of proximal humeral fractures is associated with an unexpectedly high rate of screw cutout and revision surgery, especially in patients older than sixty years who have a three or four-part fracture. The indications for open reduction and internal fixation in these patients require continued analysis. ::: ::: Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.
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paper_title: Locked vs. unlocked plate osteosynthesis of the proximal humerus - a biomechanical study.

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BACKGROUND ::: Locked plates (internal fixators) have been found to be an optimal method for the fixation in proximal humeral fractures. In a biomechanical cadaver study the difference between locked and non-locked osteosyntheses was investigated. ::: ::: ::: METHODS ::: Paired humeri were harvested, bone density measured. Locked internal fixators were mounted on one specimen; identical plate-screw-systems without locking mechanism applied to the contralateral specimen for comparison. After that, a transverse subcapital osteotomy was performed. With 7 pairs of humeri static tests with increasing axial loads and with 5 pairs dynamic tests with 10 N preload and 80 N maximal axial load for up to 1 million cycles were performed. ::: ::: ::: RESULTS ::: In the static experiments the elastic stiffness of the construct was 74% higher in the locked group (median 80 N/mm, quartile range 77-86 N/mm) compared with the non-locked group (46 N/mm, 35.5-56.5 N/mm). The difference was statistically significant (Wilcoxon test for paired samples, P<0.05). Similarly, the linear range until failure was definitely extended in the locked group by 64% (92 N, 89-98 N vs. 56 N, 36.5-73.5 N, P<0.05). Under dynamic loading the non-locked group showed fixation failures between 97,000 and 500,000 cycles. In the locked group no failure was observed until the end of the experiment at 1 million cycles (P<0.0.5). The final deformation was found to be 1 mm (median, quartil range 1.0-1.2 mm) in the non-locked group and 0.3 mm (0.2-0.3 mm) in the locked group (P<0.05). The differences were found equally in lower as well as in higher bone density specimen. ::: ::: ::: INTERPRETATION ::: Because of the optimal load transfer between implant and cancellous bone, a locked screw plate interface will reduce fixation failure in proximal humeral fractures.
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paper_title: Intramedullary cortical bone strut improves the cyclic stability of osteoporotic proximal humeral fractures

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Proximal humeral fractures treated with locking plate can fail due to varus collapse, especially in osteoporotic bone with medial cortex comminution. The use of an intramedullary strut together with locking plate fixation may strengthen fixation and provide additional medial support to prevent the varus malalignment. This study biomechanically investigates the influence of an intramedullary cortical bone strut on the cyclic stability of proximal humeral fractures stabilized by locking plate fixation in a cadaver model. Ten cadaveric humeri were divided into two groups statistically matched for bone density. Each specimen was osteotomized with 10 mm gap at the surgical neck. The non-augmented group stabilized with locking plate alone; in the augmented group, a locking plate was used combined with an intramedullary cortical bone strut. The strut was retrograded into the subchondral bone, and three humeral head screws were inserted into the strut to form a plate-screw-strut mechanism. The cyclic axial load was performed to 450 N for 6000 cycles and then loaded to failure. Construct stiffness, cyclic loading behavior and failure strength were analyzed to identify differences between groups. The augmented constructs were significantly stiffer than the non-augmented constructs during cycling. On average, the maximum displacements at 6000 cycles for non-augmented and augmented groups were 3.10 ± 0.75 mm and 1.7 ± 0.65 mm (p = 0.01), respectively. The mean peak-to-peak (inter cycle) displacement at 6000 cycles was about 2 times lower for the augmented group (1.36 ± 0.68 mm vs. 2.86 ± 0.51 mm). All specimens showed varus collapse combined with loss of screw fixation of the humeral head. The failure load of the augmented group was increased by 2.0 (SD = 0.41) times compared with the non-augmented group (p < 0.001). The stability and strength of the locking plate augmented with an intramedullary strut were significantly increased. For bone with poor quality, the subsidence of the locked screws led larger displacement, decreased the stability of the constructs, however, the plate-screw-strut mechanism provided more rigidity to stabilize the fixation. This study emphasized the importance of intramedullary support for the proximal humeral fractures fixed with a locked plate under cyclic loading, especially in bone with poor quality. This work is based on the results of cadaver model, further in vivo analysis is necessary to determine if the clinical results can be extrapolated from this data.
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paper_title: Surgical neck fractures of the proximal humerus : a laboratory evaluation of ten fixation techniques

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Objective : A biomechanical cadaver study was performed to compare the stability and ultimate strength of ten standard fixation techniques used for the treatment of surgical neck fractures of the proximal humerus. Design : One hundred twenty (60 fresh frozen, 60 embalmed) proximal humerus specimens were selected and divided into two groups : fresh frozen specimens represented a nonosteopenic group and embalmed specimens an osteopenic group. Simulated fractures were created at the level of the surgical neck, reduced, and randomly assigned to one of ten methods of fixation (six fresh frozen and six embalmed specimens per fixation group). These constructs were then mechanically tested with the humeri oriented to create primarily shear loading of the fixation. Results and Conclusions : The T-plate and screws provided significantly stronger fixation (p < 0.005) in the fresh frozen specimens than all other methods. The Ender nails/tension band construct was the second strongest fixation technique, providing significantly stronger fixation (p < 0.01) than all the remaining techniques. Four Schanz pins with one pin placed through the greater tuberosity followed by the T-plate and screws provided the strongest fixation in embalmed specimens. Tension band fixation in both humeral groups was shown to provide the least effective fixation.
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paper_title: The Mechanical Benefit of Medial Support Screws in Locking Plating of Proximal Humerus Fractures

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Background ::: The purpose of this study was to evaluate the biomechanical advantages of medial support screws (MSSs) in the locking proximal humeral plate for treating proximal humerus fractures.
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paper_title: Locking Plate Fixation with and without Inferomedial Screws for Proximal Humeral Fractures: A Biomechanical Study

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PURPOSE. To compare the efficacy of locking plate fixation with and without inferomedial screws in maintaining the reduction of a proximal humeral fracture. METHODS. 22 synthetic humerus models were used. A standardised 3-part proximal humeral fracture with a 4-mm wedge segment was created and fixed with a locking plate and screws with (n=11) and without (n=11) inferomedial screws. The intrafragmentary motion of the construct at 250, 500, 750, and 1000 cycles of 532 N loading, and the load to failure of the 2 groups were compared. RESULTS. Locking plate fixation with inferomedial screws reduced the mean intrafragmentary motion in all cycles (p<0.01) and increased the load to failure (1452 N vs. 1159 N, p<0.001), compared to fixation without inferomedial screws. CONCLUSION. Additional inferomedial screws provide medial column support for fracture healing. This may reduce intrafragmentary motion and thus implant complications resulting from varus malalignment such as screw perforation or loss of reduction.
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paper_title: Biomechanics of four techniques for fixation of the four-part humeral head fracture

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OBJECTIVE ::: To carry out a biomechanical study of four techniques for fixation of four-part humeral head fractures. ::: ::: ::: METHODS ::: The fracture was reproduced in 40 plastic humeri, divided into groups of ten according to the fixation technique, each one employing different fixation resources, in different configurations. The humeral models were mounted on an aluminum scapula, with leather straps simulating the rotator cuff tendons, and submitted to bending and torsion tests in a universal testing machine, using relative stiffness as an evaluation parameter. Assemblies with intact humeri were analyzed for comparison. ::: ::: ::: RESULTS ::: The biomechanical behavior of the fixation techniques varied within a wide range, where the assemblies including the DCP plate and the 4.5mm diameter screws were significantly more rigid than the assemblies with the Kirschner wires and the 3.5mm diameter screws. ::: ::: ::: CONCLUSION ::: The four fixation techniques were able to bear loads compatible with the physiological demand, but those with higher relative stiffness should be preferred for clinical application. ::: ::: ::: LABORATORY INVESTIGATION ::: .
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paper_title: Anatomical and biomechanical evaluation of an intramedullary nail for fractures of proximal humerus fractures based on tuberosity fixation.

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BACKGROUND ::: For unstable proximal humerus fractures, both plates and nails may be recommended. We introduce an anterograde nail designed for the treatment of 3- and 4-parts proximal humerus fractures. The aim of this study is to compare the biomechanics of this nail versus a plate and then to analyze the relationships of the screws with the axillary nerve. Our working hypotheses are as follows: (1) this nail is biomechanically equal or better to the reference plate and (2) it does not endanger the axillary nerve. ::: ::: ::: METHODS ::: Biomechanical study: using 40 sawbones, a reproducible 4-part fracture was created and fixed first with an angle-stable plate for proximal humeral fracture, then fixed with the nail using 2 posterior screws. All specimens were mounted in a custom testing apparatus. Two trails were performed needing each time 5 "normal" and 5 "osteoporotic" bones. ::: ::: ::: ANATOMICAL STUDY ::: On 20 unpaired shoulders, a nail was inserted with all screws through a superior approach (deltoid split approach). Dissection of all shoulders was done to identify the axillary nerve. The distance between each screw and the axillary nerve or its branches was measured. ::: ::: ::: FINDINGS ::: The proximal humerus nail demonstrated higher values than locking plate for both stiffness and load to failure. The failure mode differs in function of the type of osteosynthesis. The lowest distance between a screw and the axillary nerve was 20.13 mm. ::: ::: ::: INTERPRETATIONS ::: We introduce a biomechanically efficient nail without increased neurological risks to improve the pullout strength of the screws to provide more secure fixation of proximal humeral fractures. ::: ::: ::: LEVEL OF EVIDENCE ::: Basic Science Study, Anatomic Cadaver Study.
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paper_title: Medial support by fibula bone graft in angular stable plate fixation of proximal humeral fractures: an in vitro study with synthetic bone.

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BACKGROUND ::: Failure to achieve stable fixation with medial support in proximal humeral fractures can result in varus malalignment and cut-through of the proximal screws. The purpose of this study was to investigate the influence of an intramedullary fibula bone graft on the biomechanical properties of proximal humeral fractures stabilized by angular stable plate fixation in a bone model under cyclic loading. ::: ::: ::: METHODS ::: Two fixation techniques were tested in 20 composite analog humeri models. In group F- (n = 10), fractures were fixed by an anatomically formed locking plate system. In group F+ (n = 10), the same fixation system was used with an additional fibular graft model with a length of 6 cm inserted in an intramedullary manner. Active abduction was simulated for 400 cycles by use of a recently established testing setup. Fragment gap distance was measured, and thereby, intercyclic motion, fragment migration, and residual plastic deformation were determined. ::: ::: ::: RESULTS ::: The addition of a fibular graft to the fixation plate led to 5 times lower intercyclic motion, 2 times lower fragment migration, and 2 times less residual plastic deformation. Neither screw pullout, cut-through, nor implant failure was observed. ::: ::: ::: CONCLUSION ::: Medial support with an intramedullary fibular graft in an angular stable fixation of the proximal humerus in vitro increases overall stiffness of the bone-implant construct and reduces migration of the humeral head fragment. This technique might provide a useful tool in the treatment of displaced proximal humeral fractures, especially when there is medial comminution.
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paper_title: Biomechanical Analysis of Blade Plate Versus Locking Plate Fixation for a Proximal Humerus Fracture: Comparison Using Cadaveric and Synthetic Humeri

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Objective:To compare the mechanical stability of a fixed-angle blade plate with that of a locking plate in a cadaveric proximal humerus fracture-fixation model subjected to cyclic loading. A secondary objective was to evaluate whether the use of synthetic humerus specimens would replicate significan
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paper_title: Proximal humeral fracture fixation: a biomechanical comparison of two constructs.

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BACKGROUND ::: Different options exist for stabilizing proximal humeral fractures. This study compared the mechanical stability of 2 common proximal humeral fixation plates in bending and torsion. ::: ::: ::: METHODS ::: Tests were conducted on 40 synthetic and 10 matched pairs of cadaveric humeri (evenly fixed with DePuy S3 proximal humeral plating system [DePuy Orthopaedics, Warsaw, IN, USA] and Synthes proximal humerus locking compression plate [Synthes, Paoli, PA, USA]). Half of the humeri were tested by cantilevered bending in flexion, extension, varus, and valgus for 100 cycles of ±5 mm of displacement at 1 mm/s before loading to failure in varus. The other half were tested in torsion for 100 cycles of ±8° of rotational displacement at 1°/s before loading to failure in external rotation. ::: ::: ::: RESULTS ::: Peak cyclic loads for synthetic constructs were higher for DePuy plates than Synthes plates in varus and valgus (P < .0001), but a difference was not detected in extension (P > .40) or flexion (P = .0675). Peak cyclic loads for cadaveric constructs showed a significant difference in extension and flexion (Synthes > DePuy, P < .0001) and in varus (DePuy > Synthes, P < .05) but not in valgus (P > .10). Bending stiffness during varus failure testing was higher for DePuy plates than Synthes plates (P < .0001) for synthetic constructs. Regarding torsion of synthetic and cadaveric constructs, DePuy plates experienced higher peak cyclic torques over all cycles in both directions (P < .0001). For synthetic constructs, DePuy plates showed higher torsional stiffness in external failure than Synthes plates (P < .0001). ::: ::: ::: CONCLUSIONS ::: The DePuy plate was stiffer than the Synthes plate with varus and valgus bending, as well as in torsion. The Synthes plate tended to be stiffer in flexion and extension.
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paper_title: The Biomechanics of Locked Plating for Repairing Proximal Humerus Fractures With or Without Medial Cortical Support

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Background:Comminuted proximal humerus fracture fixation is controversial. Locked plate complications have been addressed by anatomic reduction or medial cortical support. The relative mechanical contributions of varus malalignment and lack of medial cortical support are presently assessed.Methods:F
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paper_title: A mechanical comparison between conventional and modified angular plates for proximal humeral fractures.

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The objective of this study is to present a modified angular blade plate for fixing 2-part and even 3-part fractures of the proximal humerus, as well as the results of the comparative mechanical test between the conventional angular blade plate and this new modified plate. The plates were tested in flexion and rotational trials in a wooden model that simulated a 2-part humeral fracture of the proximal extremity. The results (mean +/- SD) of bending strength and stiffness obtained after testing showed findings of 601 +/- 349 N and 0.5 +/- 0.2 N/mm, respectively, for the conventional plate and 4005 +/- 164 N and 3.9 +/- 0.7 N/mm, respectively, for the modified plate. The torsional stiffness test showed findings of 1.26 +/- 0.09 KN.mm degrees for the conventional plate and 1.74 +/- 0.21 KN.mm degrees for the modified plate. The test of torsional moment showed findings of 57.0 +/- 7.6 KN.mm for the conventional plate and 115.2 +/- 9.3 KN.mm for the modified plate. The test of angular displacement at the torsional moment showed findings of 50.8 degrees +/- 7.2 degrees for the conventional plate and 70.2 degrees +/- 2.6 degrees for the modified plate. The results of the mechanical trials of flexion and rotation were superior for the modified angular blade plate compared with the conventional angular blade plate.
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paper_title: The Mechanical Benefit of Medial Support Screws in Locking Plating of Proximal Humerus Fractures

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Background ::: The purpose of this study was to evaluate the biomechanical advantages of medial support screws (MSSs) in the locking proximal humeral plate for treating proximal humerus fractures.
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paper_title: A BIOMECHANICAL COMPARISON OF LOCKING PLATE AND LOCKING NAIL IMPLANTS USED FOR FRACTURES OF THE PROXIMAL HUMERUS.

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The aim of this study was to determine the biomechanical behavior of two different implants used in the fixation of proximal humerus fractures. The two implants in this study are specifically designed for the fixation of proximal humerus fractures and both utilize the concept of fixed angle locking screws. Bone densitometry was performed prior to fracture production and fixation. A reproducible three-part fracture was created in paired human cadaveric bone and then fixed using the locking screw implants. Stress/strain curves for the bone-implant construct were created for loads applied in cantilever bending and torsion to determine the relative stiffness below the yield point. Following this each construct was tested to failure with a valgus bending load. The locking nail implant provided a significantly stiffer construct in torsion, valgus, extension and flexion at loads below failure threshold. The valgus load to failure was significantly higher for the nail. The mode of failure was different between implants.
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paper_title: How does a varus deformity of the humeral head affect elevation forces and shoulder function? A biomechanical study with human shoulder specimens.

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OBJECTIVES ::: A biomechanical study was performed to test the hypothesis that a varus deformity of the humeral head decreases supraspinatus (SSP) efficiency and increases deltoid elevation forces in human specimens. ::: ::: ::: METHODS ::: Twenty-four fresh-frozen human shoulder specimens were prepared by preserving the rotator cuff and deltoid. A defined, medial closed-wedge osteotomy was performed and lateral locked plate applied to simulate a varus deformity of 45° in Group I (n = 8) and 20° in Group II (n = 8). The control group (n = 8) was not osteotomized. The effect of the deformities on arm elevation forces was measured in a robot-assisted shoulder simulator under a physiologically loaded rotator cuff during three elevation phases. Phase 1 encompassed 0° to 30°, Phase 2 was from 30° to 60°, and Phase 3 included 60° to 90° of shoulder elevation. ::: ::: ::: RESULTS ::: SSP efficiency, defined as the degree of elevation attained per unit muscle force, was significantly less in Group I compared with Group II (P = 0.036) and the control group (P = 0.039) (Group I = 0.12 ± 0.03°/N, Group II 0.18 ± 0.05°/N, and control group 0.24 ± 0.10°/N). Under physiological loading of the rotator cuff, the deltoid (DELT) elevation forces were significantly greater in Group I (Pphase 1 = 0.015, Pphase 3 = 0.001) and Group II (Pphase 1 = 0.015, Pphase 3 = 0.006) compared with the control group in elevation Phase 1 (Group I: 3.20 ± 1.04 N/°, Group II: 3.03 ± 0.96 N/°, control group: 2.01 ± 0.53 N/°) and Phase 3 (Group I: 2.50 ± 0.85 N/°, Group II: 1.55 ± 0.28 N/°, control group: 1.21 ± 0.18 N/°). When the SSP was unloaded, the DELT elevation forces were significantly greater in Group l than in Group II (P = 0.040) and the control group (P = 0.004) during elevation Phase 3 (Group I: 2.12 ± 0.60 N/°, Group II: 1.47 ± 0.34 N/°, control group: 1.24 ± 0.32 N/°). ::: ::: ::: CONCLUSIONS ::: A varus deformity of the humeral head changes the pretension of the rotator cuff and results in a significantly decreased SSP efficiency (45° varus) and significantly higher arm elevation forces (20° varus). Clinically, the study's findings are relevant because they indicate that varus deformities of more than 20° should not be accepted intraoperatively and might indicate the need for surgical correction in case of subsequent symptoms.
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paper_title: Locking plate fixation of humeral head fractures with a telescoping screw. A comparative biomechanical study versus a standard plate.

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OBJECTIVES ::: Locking plate fixation of humeral head fractures bares the risk of glenohumeral screw penetration. In order to circumvent this problem it is recommended to insert shorter locking screws having at least a 6mm distance to the humeral head cortex. This in turn may reduce fixation stability and may lead to early varus displacement. One second frequent failure mechanism is cranial displacement of the greater tubercle. The study evaluates the biomechanical properties of a locking plate employing an additional telescoping screw that may enhance resistance to varus displacement. Screw in screw fixation of the greater tubercle may reduce the rate of cranial displacement. ::: ::: ::: METHODS ::: In four paired fresh-frozen human cadaver humeri (age>70 years) a Neer IV/3 fracture was created with a 5mm osteotomy gap simulating metaphyseal comminution. Limbs were randomly assigned to receive plate fixation with an additional telescoping screw (Humerus Tele Screw: HTS) and on the contralateral limb Philos plate fixation before biomechanical evaluation (MTS-Bionix 858.2). Standard locking screws were placed in both groups 6mm below the radiological head circumference; the telescoping screw was placed in the subchondral layer. The greater tubercle was fixed with an additional screw in both techniques, in the HTS group the screw was anchored in the sleeve of the telescrew (screw in screw fixation). ::: ::: ::: FINDINGS ::: Fixation stability with a mean stiffness of 300.9±28.8 N/mm in the HTS plate group proved to be significantly higher than in the Philos plate group (184.2±23.4 N/mm; p=0.006). The HTS plate also resisted higher loads in terms of fixation failure with loss of reduction at 290±58.6 N in comparison to 205±8.6 N for the Philos plate (p=0.2). Displacement of the greater tubercle occurred in no case of the HTS plate group and in two out of four cases in the Philos plate group. ::: ::: ::: INTERPRETATION ::: The HTS plate provides high fixation stability in an in vitro humeral head fracture model and securely prevents displacement of the greater tubercle.
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paper_title: Biomechanical effects of calcar screws and bone block augmentation on medial support in locked plating of proximal humeral fractures

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Abstract Background The objective of this study was to investigate the biomechanical effects of medial fracture gap augmentation in locked plating of an unstable 2-part proximal humeral fracture with calcar screws and insertion of a corticocancellous bone block. Furthermore the mechanical behavior of dynamic locking screws in the non-parallel arrangement of a proximal humeral plate was of interest. Methods Thirty-two fresh frozen humeri were randomized in four equal groups. An unstable 2-part fracture was fixed by locked plating in all specimens. The basic screw setup was supplemented by additional calcar screws in one group. Humeral head screws were replaced by dynamic locking screws in a second group. The third group featured an additional corticocancellous femoral head allograft. Assessment of stiffness was followed by cyclic loading and load to failure tests. Resulting stiffness, fracture gap deflection and ultimate load were compared utilizing Bonferroni corrected t-test for independent samples. Findings The mechanical effect of additional calcar screws was non-significant as compared to the basic screw configuration whereas bone block insertion significantly increased construct stiffness and failure load. The use of dynamic locking screws did not significantly reduce construct stiffness when compared to conventional locking screws. Interpretation Additional calcar screws alone did not improve the initial biomechanical properties of an unstable 2-part proximal humeral fracture model. However bone block augmentation appeared to be a reliable alternative of additional bony support by raising stiffness and failure load. Dynamic locking screws did not show their expected dynamic component when used in a non-parallel arrangement.
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paper_title: Straining of the intact and fractured proximal humerus under physiological-like loading.

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Surgical treatment of proximal humeral fractures remains challenging in elderly patients, primarily due to insufficient implant fixation. Both bone quality and physiological-like loading conditions are commonly overlooked during pre-clinical in vitro evaluation. However, this knowledge is necessary in order to improve surgical treatment of the proximal humerus and the mechanical behavior of implants, particularly in patients with complex fractures and weak bone stock. We hypothesize that the bone quality has a high influence on the bone straining, independent of the arm position. The goal of this study was to determine the straining of the intact and fractured proximal humerus under physiological-like loading conditions. Furthermore, the impact of augmentation on tissue straining was evaluated. Two representative humeri were selected for this study, one osteoporotic and one reference quality, and scanned using both QCT and DEXA (average DEXA value=0.26 and 0.49 g/cm2 respectively). Subcaptial defects were generated, then stabilized with a plate prior to mechanical stiffness testing. From the QCT data, finite element models were generated and the in vitro stiffness tests analytically simulated. Under physiological-like loading conditions, the straining of the bone and implant were analyzed for 0 degrees, 90 degrees forward flexion, and 90 degrees abduction. Maximal strain values were found for the intact and fractured bone at 90 degrees abduction. This study demonstrates that the straining in a fractured bone of poor quality leads to considerably higher bone strains (up to +30%) than in a more healthy bone. Augmentation of a central void under physiological-like loading with commercial cement led to mechanical failure at the bone-cement interface. New concepts for the surgical treatment of complex fractures of the proximal humerus should take bone distribution into account and thereby allow effective treatment of fractures in osteoporotic patients. The ultimate salvage procedure of augmentation has mechanical limitations as long as current cement materials are used in osteoporotic patients.
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paper_title: Biomechanical Evaluation of Locking Plate Fixation of Proximal Humeral Fractures Augmented With Calcium Phosphate Cement

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OBJECTIVES ::: To evaluate the influence of calcium phosphate cement augmentation on failure of locking plate fixation of proximal humeral fracture fixation in a cadaveric fracture model. ::: ::: ::: METHODS ::: A 5-mm wedge osteotomy was created in each of 11 paired fresh-frozen human cadaveric humeri (age > 65 years). Specimens were randomly assigned to receive either locked plate fixation (group 1) or locked plate fixation with cement augmentation (group 2). Constructs were tested for axial stiffness, load to failure, and failure mode using a material testing machine. ::: ::: ::: RESULTS ::: Cement-augmented specimens resisted higher loads (1936 ± 609 N) in comparison to nonaugmented specimens (1373 ± 590 N) (P = 0.01). In group 1, varus displacement and glenohumeral screw perforation occurred in all cases. Varus displacement occurred in 2 cases in group 2, whereas glenohumeral screw perforation did not occur in any of the cases. Cement augmentation led to a significant increase in axial stiffness (P = 0.04). ::: ::: ::: CONCLUSIONS ::: Calcium phosphate cement-augmented locking plates enhanced fixation stability in proximal humeral fractures and reduced glenohumeral screw perforation in this 2-part cadaveric model. The ultimate advantage of this method remains to be determined in vivo.
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paper_title: 45. BIOMECHANICAL ANALYSIS OF PROXIMAL HUMERAL FIXATION USING LOCKING PLATE FIXATION WITH AN INTRAMEDULLARY FIBULAR ALLOGRAFT

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Purpose: The purpose of this study is to compare two fixation methods for surgical neck proximal humeral fractures with medial calcar comminution: locking plate fixation alone and locking plate fixation with intramedullary allograft fibular bone peg augmentation. Method: Eight embalmed pairs of cadaveric specimens were utilized in this study. Dual energy X-ray absorptiometry (DXA) scans were initially performed to determine the bone density of the specimens. Surgical neck proximal humerus fractures were simulated in these specimens by creating a 1-centimeter wedge-shaped osteotomy at the level of the surgical neck to simulate medial calcar fracture comminution. Each pair of specimens had one arm randomly repaired with locking plate fixation, and the other arm repaired with locking plate fixation augmented with an intramedullary fibular autograft bone peg. The constructs were tested in bending to determine the failure loads, and initial stiffness using Digital Imaging Correlation (DIC) technology. The moment created by the rotator cuff was replicated by fixating the humeral head, and applying a point load to the distal humerus. A load was applied with a displacement rate of 4 mm/min, and was stopped approximately every 5 lbs to take a picture and record the load. This process was continued until failure of the specimens was obtained. Results: The intramedullary bone peg autograft increased the failure load of the constructs by 1.57±0.59 times (p = 0.026). Initial stiffness of the construct was also increased 3.13±2.10 times (p = 0.0079) with use of the bone peg. Conclusion: The stronger and stiffer construct provided by the addition of an intramedullary fibular allograft bone peg to locking plate fixation may help maintain reduction, and reduce the risk of fixation failure in surgical neck proximal humerus fractures with medial comminution.
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paper_title: In vivo glenohumeral contact forces--measurements in the first patient 7 months postoperatively.

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Knowledge of forces in the glenohumeral joint is essential for understanding normal and pathologic shoulder function. It forms the basis for performing fracture treatment or joint replacement surgery, for optimizing implant design and fixation and for improving and verifying analytical biomechanical models of the shoulder. An instrumented shoulder implant with telemetric data transmission was developed to measure six components of joint contact forces and moments. A patient with humeral head arthrosis achieved good joint function after its implantation. During the first 7 postoperative months, the contact force remained below 100% BW (percent body weight) for most activities of daily living. It ranged up to 130% BW for arm positions close to the limits of motion or when acting against external resistance. When the patient tried to turn a blocked steering wheel with maximum effort, the force rose to about 150% BW, the highest level observed thus far. Of great interest were the force directions relative to the humerus, especially those in the sagittal plane, which were not greatly influenced by the type of exercise, the arm position or the external resistance. The moments due to friction in the joint reached 5.2 Nm. The friction-induced shift of contact forces relative to the implant head centre ranged up to 6.3mm. These first worldwide in vivo measurements of glenohumeral contact forces are being continued in more patients and for longer postoperative times.
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paper_title: Locking plate fixation of proximal humeral fractures with impaction of the fracture site to restore medial column support: a biomechanical study

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Background Despite the advent of locking plate techniques, proximal humeral fracture fixation can fail due to varus collapse, especially in osteoporotic bone with medial cortex comminution. This study investigated the effect of restoring the integrity of the medial column by fracture impaction and shaft medialization with locking plate fixation. This construct was compared with a traditional locking plate construct under conditions of varus cyclical loading. Materials and methods Proximal humeral fractures with medial comminution were simulated by performing wedge-shaped osteotomies at the surgical neck in cadaveric specimens and removing 1 cm of medial cortex. For each cadaver (n = 6), 1 humeral fracture was fixed with a traditional locking plate construct. The other was fixed with the locking plate construct plus fracture impaction and shaft medialization, resulting in medial column restoration. The humeral head was immobilized, and a repetitive, varus force was applied to the humeral shaft until construct collapse or until 25,000 cycles were completed. Results None of the constructs with fracture impaction collapsed, whereas 5 of 6 of the nonaugmented constructs collapsed before reaching 25,000 cycles ( P = .008). Collapse of the 5 nonimpacted constructs that failed occurred after an average of 11,470 ± 3589 cycles. Conclusion Fracture impaction increased the ability of the locking plate to withstand repetitive varus loading. This technique provides a construct biomechanically superior to locking plate fixation alone.
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paper_title: Locking Plate Fixation with and without Inferomedial Screws for Proximal Humeral Fractures: A Biomechanical Study

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PURPOSE. To compare the efficacy of locking plate fixation with and without inferomedial screws in maintaining the reduction of a proximal humeral fracture. METHODS. 22 synthetic humerus models were used. A standardised 3-part proximal humeral fracture with a 4-mm wedge segment was created and fixed with a locking plate and screws with (n=11) and without (n=11) inferomedial screws. The intrafragmentary motion of the construct at 250, 500, 750, and 1000 cycles of 532 N loading, and the load to failure of the 2 groups were compared. RESULTS. Locking plate fixation with inferomedial screws reduced the mean intrafragmentary motion in all cycles (p<0.01) and increased the load to failure (1452 N vs. 1159 N, p<0.001), compared to fixation without inferomedial screws. CONCLUSION. Additional inferomedial screws provide medial column support for fracture healing. This may reduce intrafragmentary motion and thus implant complications resulting from varus malalignment such as screw perforation or loss of reduction.
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paper_title: Proximal humerus fractures: a comparative biomechanical analysis of intra and extramedullary implants

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INTRODUCTION ::: The biomechanical stability of a newly developed humerus nail (Sirustrade mark) for the treatment of fractures of the proximal humerus was analyzed in comparison to established systems. In total, three randomized groups were formed (n = 4 pairs) from 12 matched pairs of human cadaver humeri. ::: ::: ::: MATERIALS AND METHODS ::: All intact bones were mechanically characterized by five subsequent load cycles under bending and torsional loading. The bending moment at the osteotomy was 7.5 N m the torsional moment was 8.3 N m over the hole specimen length. Loading was consistently initiated at the distal epiphysis and the deformation at the distal epiphysis was continuously recorded. Prior to implant reinforcement, a defect of 5 mm was created to simulate an unstable subcapital humerus fracture. For paired comparison, one humerus of each pair was stabilized with the Sirus proximal humerus nail while the counterpart was stabilized by a reference implant. In detail, the following groups were created: Sirus versus Proximal humerus nail (PHN) with spiral blade (group I); Sirus versus PHILOS plate (group II); Sirus versus 4.5 mm AO T-plate (group III). ::: ::: ::: RESULTS ::: The Sirus nail demonstrated significantly higher stiffness values compared to the reference implants for both bending and torsional loading. The following distal epiphyseal displacements were recorded for a bending moment of 7.5 N m at the osteotomy: Sirus I: 8.8 mm, II: 8.4 mm, III: 7.7 mm (range 6.9-10.9), PHN 21.1 mm (range 15.7-25.2) (P = 0.005), PHILOS plate 27.5 mm (range 21.6-35.8) (P < 0.001), 4.5 AO T-plate 26.3 mm (range 24.3-33.9) (P = 0.01). The rotations corresponding to 8.3 N m torsional moment were: Sirus I: 9.1 degrees , II: 9.3 degrees , III: 10.6 degrees (range 7.5-12.2), PHN 13.5 degrees (range 10.3-15.6) (P = 0.158), PHILOS plate 15.6 degrees (range 13.7-20.8) (P = 0.007), 4.5 AO T-Platte 14.1 degrees (range 11.5-19.7) (P = 0.158). ::: ::: ::: CONCLUSION ::: The intramedullary load carriers were biomechanically superior when compared to the plating systems in the fracture model presented here. Supplementary, the Sirus Nail showed higher stiffness values than the PHN. However, the latter are gaining in importance due to the possibility of minimal invasive implantation. Whether this will be associated with functional advantages requires further clinical investigation.
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paper_title: Locked plate fixation and intramedullary nailing for proximal humerus fractures: a biomechanical evaluation.

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Background: Internal fixation of proximal humeral fractures is associated with a considerable secondary malalignment rate. Fixed-angle implants have been suggested to increase the stability of fixation. Methods: The biomechanical properties of four different implants were tested. These included an internal fixator with semi-elastic properties (reference), the Synthes T-plate, a locked plate with rigid properties and a spiral blade locked intramedullary nail (PHN). These implants were assessed in twenty-four osteotomized pairs of human cadaveric humeri. Specimens were subjected to two-hundred cycles of axial loading and torque followed by load to failure. Results: The PHN had greater axial stiffness than the reference and the T-plate. During torque, all implants were stiffer than the reference. During cyclic loading, there were no differences between the T-plate and the reference. Both the rigid internal fixator and the PHN had less irreversible deformation than the reference. Both implants resisted higher loads before failure. Conclusion: This study showed that the proximal humeral nail and the rigid internal fixator are stronger than the semi-elastic locked plate and the Synthes T-plate for unstable subcapital proximal humeral fractures.
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paper_title: Relationship of cortical thickness of the proximal humerus and pullout strength of a locked plate and screw construct.

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BACKGROUND ::: No study to date has evaluated cortical thickness as it relates to locking plate failure or screw pullout in the proximal humerus. The purpose of this study is to determine the relationship between proximal humerus cortical thickness and locked plate hardware failure in a cadaveric proximal humerus fracture model. ::: ::: ::: METHODS ::: Twelve humerus specimens were placed into two groups based on the proximal humerus cortical thickness on an anteroposterior radiograph: less than 4 mm and greater than 4 mm. The specimens were plated with a six-hole proximal humerus locking plate and a 15-mm resection osteotomy at the surgical neck was performed. The specimens were tested in a materials testing machine at a displacement of 5 mm/min to failure. ::: ::: ::: RESULTS ::: Load at failure, stiffness, maximum load, failure, and fracture gap closure were all statistically similar (P > 0.05) between the groups. ::: ::: ::: CONCLUSION ::: Our biomechanical study used modern locked plate-screw construct fixation of a simulated two-part proximal humerus fracture. The mechanical strength was unaffected based on a threshold combined proximal humerus cortical thickness of 4 mm.
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paper_title: Biomechanical evaluation of glenohumeral stability through muscle force vector analysis. Effect of a decreased glenoid inclination in shoulders with global rotator cuff tears

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OBJECTIVES ::: The aim of the study was to quantify the decrease in glenohumeral stability following a global rotator cuff tear and to evaluate the effect of a decreased glenoid inclination angle through analysis of muscle force vectors in a computer model. ::: ::: ::: MATERIAL AND METHODS ::: The lines of action of eight shoulder muscles were integrated into a standard geometric model. Muscle force magnitudes were estimated based on physiological cross-sectional area and normalized electromyographic activity. The magnitude and elevation angle of the resultant force vector was calculated at 0, 30, 60, and 90 degrees of abduction. A rotator cuff tear was simulated by reduction of the corresponding muscle force vectors. ::: ::: ::: RESULTS ::: At 0 and 30 degrees of glenohumeral abduction a global rotator cuff tear showed a resultant force vector pointing outside the glenoid. In the computer model, decreasing the inclination angle of the glenoid by 30 degrees increased the stability in rotator cuff-deficient shoulders. ::: ::: ::: CONCLUSIONS ::: The results of this study provide a biomechanical rationale for clinical complications of global rotator cuff tear such as superior humeral head translation. The decreased glenoid inclination simulated in the computer model may represent a biomechanical basis for the development of new operative techniques to treat global rotator cuff tears.
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paper_title: Two-part surgical neck fractures of the proximal part of the humerus. A biomechanical evaluation of two fixation techniques.

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Background: Successful internal fixation of fractures of the surgical neck of the humerus can be difficult to achieve because of osteopenia of the proximal aspect of the humerus. The purpose of this study was to compare the biomechanical stability of a proximal humeral intramedullary nail and a locking plate for the treatment of a comminuted two-part fracture of the surgical neck in a human cadaver model. ::: ::: Methods: Twenty-four cadaveric humeri were instrumented with use of either a titanium proximal humeral nail (PHN) or a 3.5-mm locking compression plate for the proximal part of the humerus (LCP-PH). The specimens were matched by bone mineral density and were separated into four experimental groups with six humeri in each: PHN bending, LCP-PH bending, PHN torsion, or LCP-PH torsion. Comminuted fractures of the surgical neck were simulated by excising a 10-mm wedge of bone. Bending specimens were cyclically loaded from 0 to 7.5 Nm of varus bending moment at the fracture site. Torsion specimens were cyclically loaded to ±2 Nm of axial torque. The mean and maximum displacement in bending, mean and maximum angular rotation in torsion, and stiffness of the bone-implant constructs were compared. ::: ::: Results: In bending, the LCP-PH group demonstrated significantly less mean displacement of the distal fragment than did the PHN group over 5000 cycles (p = 0.002). In torsion, the LCP-PH group demonstrated significantly less mean angular rotation than did the PHN group over 5000 cycles (p = 0.04). A significant number of specimens in the PHN group failed prior to reaching 5000 cycles (p = 0.04). The LCP-PH implant created a significantly stiffer bone-implant construct than did the PHN implant (p = 0.007). ::: ::: Conclusions: The LCP proximal humeral plate demonstrated superior biomechanical characteristics compared with the proximal humeral nail when tested cyclically in both cantilevered varus bending and torsion. The rate of early failure of the proximal humeral nail could reflect the high moment transmitted to the locking proximal screw-bone interface in this implant. ::: ::: Clinical Relevance: The high failure rate in torsion of the proximal humeral nail-bone construct is concerning, and, with relatively osteoporotic bone and early motion, the results could be poor.
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paper_title: Biomechanical Contribution of Tension-Reducing Rotator Cuff Sutures in 3-Part Proximal Humerus Fractures.

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OBJECTIVES ::: Using a cadaveric 3-part fracture model and cyclic loading protocol, our study objectives were to quantify the stabilizing effect of tension-reducing rotator cuff sutures in terms of fracture displacement across the surgical neck and greater tuberosity compared with a control group in which no sutures were used. ::: ::: ::: METHODS ::: Six matched pairs of fresh frozen specimens underwent a standardized, 3-part, proximal humerus fracture and were split into 2 groups. The control group had the fracture fixed with a plate and screw construct only while the experimental group had additional suture fixation through the plate to each rotator cuff tendon. Active abduction through the rotator cuff was simulated for 100, 200, 300, and 400 cycles and to failure at 1000 N. A Mann-Whitney U test compared cyclic displacement of the greater tuberosity and surgical neck fracture gaps and load to failure between the 2 groups. ::: ::: ::: RESULTS ::: There was no significant difference (P > 0.05) in fracture gap between fixation methods at the surgical neck at 100 (P = 0.13), 200 (P = 0.07), 300 (P = 0.49), and 400 (P = 0.07) cycles. There was no significant difference (P > 0.05) between fixation methods in the fracture gap at the greater tuberosity at 100 (P = 0.39), 200 (P = 1.00), 300 (P = 0.31), and 400 (P = 0.59) cycles. There was no significant difference (P > 0.5) at 1000 N at the surgical neck (P = 0.70) or the greater tuberosity (P = 0.39). ::: ::: ::: CONCLUSIONS ::: Tension-relieving rotator cuff sutures do not add stability to the repair of 3-part proximal humerus fractures. Varus collapse and greater tuberosity displacement are common complications associated with 3-part fractures. No mechanical data exist to demonstrate benefit of adding suture to a plate and screw construct for limiting fracture displacement.
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paper_title: Mechanical Assessment of Local Bone Quality to Predict Failure of Locked Plating in a Proximal Humerus Fracture Model

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The importance of osteoporosis in proximal humerus fractures is well recognized. However, the local distribution of bone quality in the humeral head may also have a significant effect because it remains unclear in what quality of bone screws of standard implants purchase. The goal of this study was to investigate whether the failure of proximal humerus locked plating can be predicted by the DensiProbe (ARI, Davos, Switzerland). A 2-part fracture with metaphyseal impaction was simulated in 12 fresh-frozen human cadaveric humeri. Using the DensiProbe, local bone quality was determined in the humeral head in the course of 6 proximal screws of a standard locking plate (Philos; Synthes GmbH, Solothurn, Switzerland). Cyclic mechanical testing with increasing axial loading until failure was performed. Bone mineral density (BMD) significantly correlated with cycles until failure. Head migration significantly increased between 1000 and 2000 loading cycles and significantly correlated with BMD after 3000 cycles. DensiProbe peak torque in all screw positions and their respective mean torque correlated significantly with the BMD values. In 3 positions, the peak torque significantly correlated with cycles to failure; here BMD significantly influenced mechanical stability. The validity of the DensiProbe was proven by the correlation between its peak torque measurements and BMD. The correlation between the peak torque and cycles to failure revealed the potential of the DensiProbe to predict the failure of locked plating in vitro. This method provides information about local bone quality, potentially making it suitable for intraoperative use by allowing the surgeon to take measures to improve stability.
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paper_title: Biomechanical analysis of plate osteosynthesis systems for proximal humerus fractures.

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OBJECTIVES ::: To biomechanically assess five proximal, humeral, fracture-plate-fixation systems. ::: ::: ::: METHODS ::: Surgical neck fractures, with and without cortical contact, were created in 25 fresh-frozen cadaveric humeri. Five methods of plate fixation were used for repair: construct A [an eight-hole, low contact dynamic compression (LCDC) plate contoured into a blade shape, supported by one, 70-mm-long, 4.5-mm-diameter cortical screw acting as a truss], construct B (a 10-hole LCDC plate arrangement identical to construct A, but using one, 70-mm-long, 3.5-mm-diameter cortical screw as a truss), construct C [a five-hole dynamic compression (DC) blade plate with one, 6.5-mm-diameter cancellous screw], construct D (a five-hole T-plate supported by three, 6.5-mm-diameter cancellous screws), and construct E (a five-hole cloverleaf plate supported by five, 4-mm-diameter cancellous screws). Plates were posterior to the bicipital groove, 10 mm distal to the greater tuberosity tip, on the lateral aspect of the humeral shaft. Screw fixation was done using standard AO compression plating techniques. Stiffness of constructs was measured in bending and axial compression. Locked plates were not assessed. ::: ::: ::: RESULTS ::: For cortical contact [abduction of 20 degrees (P=0.02), flexion of 20 degrees (P=0.02), flexion of 90 degrees (P=0.005)] and no cortical contact [flexion of 90 degrees (P=0.0001)], construct A was significantly stiffer than other constructs. For no cortical contact in abduction of 90 degrees (P=0.05), construct A was significantly stiffer than other constructs. ::: ::: ::: CONCLUSIONS ::: Construct A was significantly stiffer than other constructs.
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paper_title: The biomechanical performance of locking plate fixation with intramedullary fibular strut graft augmentation in the treatment of unstable fractures of the proximal humerus

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We evaluated the biomechanical properties of two different methods of fixation for unstable fractures of the proximal humerus. Biomechanical testing of the two groups, locking plate alone (LP), and locking plate with a fibular strut graft (LPSG), was performed using seven pairs of human cadaveric humeri. Cyclical loads between 10 N and 80 N at 5 Hz were applied for 1,000,000 cycles. Immediately after cycling, an increasing axial load was applied at a rate of displacement of 5 mm/min. The displacement of the construct, maximum failure load, stiffness and mode of failure were compared. The displacement was significantly less in the LPSG group than in the LP group (p = 0.031). All maximum failure loads and measures of stiffness in the LPSG group were significantly higher than those in the LP group (p = 0.024 and p = 0.035, respectively). In the LP group, varus collapse and plate bending were seen. In the LPSG group, the humeral head cut out and the fibular strut grafts fractured. No broken plates or screws were seen in either group. We conclude that strut graft augmentation significantly increases both the maximum failure load and the initial stiffness of this construct compared with a locking plate alone.
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paper_title: Retrograde nailing versus locking plate osteosynthesis of proximal humeral fractures: a biomechanical study

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Background In locking plate osteosynthesis of proximal humeral fractures, secondary varus malalignment is a specific complication. Retron nails (Tantum AG, Neumunster, Germany), among others, have been designed to improve medial support of the calcar humeri. The aim of our biomechanical study was to examine whether Retron nails provide increased stiffness for axial loads and adequate stiffness for torsional loads when compared with Philos plates (Synthes AG, Umkirch, Germany). Materials and methods Twenty-two fresh-frozen paired humeri were collected. After potting the specimens, intact bones were exposed to sinusoidal axial (10-120 N) and torsional (±2.5 Nm) loading for 8 cycles to calculate the initial stiffness and exclude pairs with differences. Afterward, an unstable proximal humeral fracture (AO 11-A3) was created by means of an oscillating saw, and the respective osteosynthesis devices were implanted. After another 4 cycles, initial changes in stiffness were measured. Subsequently, all specimens were tested for 1,000 cycles of loading before final stiffness was assessed. Results We found no statistically significant differences between Retron and Philos specimens after 4 or 1,000 cycles of loading. Conclusion Our study suggests that retrograde nailing provides sufficient stability for axial and torsional loading in 2-part fractures of proximal humeri.
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paper_title: The Role of Medial Comminution and Calcar Restoration in Varus Collapse of Proximal Humeral Fractures Treated with Locking Plates

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Background: Proximal humeral fractures that are treated with locked plate constructs remain susceptible to collapse into a varus position. The objectives of the present study were to examine how medial comminution affects fracture stability and to determine the effect of calcar fixation on osteosynthesis stability. ::: ::: Methods: Eleven matched pairs of cadaveric humeri were osteotomized to create standard three-part fractures involving the surgical neck and the greater tuberosity. Five matched pairs were randomly assigned to have the medial calcar region remain intact. Six matched pairs had removal of a 10-mm medially based wedge of bone to simulate medial comminution. All fractures were stabilized in a uniform fashion with a proximal humeral locking plate. The constructs were secured, and the superior portion of the humeral head was subjected to compressive loading to induce varus collapse. Load-to-failure and energy-to-failure values along with stiffness and displacement at the time of failure were determined. ::: ::: Results: Medial comminution decreased the mean load to failure by 48% (523 N) (p = 0.015) and the mean energy to failure by 44% (2009 Nmm) (p = 0.013). The use of calcar screw fixation increased the mean load to failure by 31% (219 N) (p = 0.002) and the mean energy to failure by 44% (1279 Nmm) (p = 0.006). ::: ::: Conclusions: Medial comminution significantly decreased the stability of proximal humeral fracture fixation constructs. Calcar restoration with screw fixation significantly improved the stability of repaired fractures in cadaveric specimens. ::: ::: Clinical Relevance: The data suggest that medial comminution is a predictor of poor stability of proximal humeral fractures and that stability may be improved through calcar restoration.
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paper_title: Effect of Calcar Screw Use in Surgical Neck Fractures of the Proximal Humerus With Unstable Medial Support: A Biomechanical Study.

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To evaluate the effect of calcar screw use in proximal humeral fractures with unstable medial support treated with locked plates.Standard osteotomies were performed in 36 cadaveric humeri to create a surgical neck fracture proximal humeral model. For static testing, 12 pairs of humeri were divided into 4 groups: normal alignment and varus deformity groups with and without 5-mm medial deficiencies. Calcar screw function was measured in each group by axial, shear, and torsion stiffness tests. Another 6 pairs of humeri with 5-mm medial deficiencies were subjected to cyclic loading tests in the normal alignment model with and without calcar screw application.Calcar screws improved rotational stability in the normal alignment (P = 0.007) and varus (P = 0.002) groups. Calcar screws improved static and cyclic axial (P = 0.004) and shear (P = 0.017) stability in the normal alignment group with medial deficiency. In specimens with normal alignment and intact medial cortex, calcar screws provided no advantage in axial (P = 0.535) or shear (P = 0.537) stiffness. Calcar screws did not provide sufficient axial (P = 0.782) or shear (P = 0.772) stability to avoid reduction loss in humeri with varus malreduction.In humeri with normal alignment, calcar screws can provide additional stability even when a medial deficiency exists. The use of calcar screws in humeri with varus deformity showed no biomechanical superiority.
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paper_title: Mechanical evaluation of a new minimally invasive device for stabilization of proximal humeral fractures in elderly patients: a cadaver study.

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BACKGROUND ::: Treatment of proximal humerus fractures in elderly patients is challenging because of reduced bone quality. We determined the in vitro characteristics of a new implant developed to target the remaining bone stock, and compared it with an implant in clinical use. ::: ::: ::: METHODS ::: Following osteotomy, left and right humeral pairs from cadavers were treated with either the Button-Fix or the Humerusblock fixation system. Implant stiffness was determined for three clinically relevant cases of load: axial compression, torsion, and varus bending. In addition, a cyclic varus-bending test was performed. ::: ::: ::: RESULTS ::: We found higher stiffness values for the humeri treated with the ButtonFix system--with almost a doubling of the compression, torsion, and bending stiffness values. Under dynamic loading, the ButtonFix system had superior stiffness and less K-wire migration compared to the Humerusblock system. ::: ::: ::: INTERPRETATION ::: When compared to the Humerusblock design, the ButtonFix system showed superior biomechanical properties, both static and dynamic. It offers a minimally invasive alternative for the treatment of proximal humerus fractures.
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paper_title: Proximal humerus fracture rotational stability after fixation using a locking plate or a fixed-angle locked nail: The role of implant stiffness

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Abstract Background Fixed-angle locked devices have been developed to improve internal fixation of proximal humerus fractures. Available low-profile precontoured locking plates and intramedullary nails with fixed-angle interlocks are currently favored by most surgeons in this setting. The aim of this study was to assess the relative stability of these two methods of fixation under torsion load. Methods A surgical neck osteotomy was created in six pairs of embalmed humeri. In each pair, one specimen was secured with a titanium locking-compression plate, and the contralateral was secured with a titanium nail with a proximal locked spiral blade. The specimens were first tested cyclically in internal–external rotation for 10,000 cycles to evaluate interfragmentary motion (dynamic study). At the end of the cyclic testing, the specimens were loaded to failure in external rotation to measure torque to failure and construct stiffness (static study). Findings There were no significant differences in interfragmentary motion between the two fixation devices in the dynamic study. When tested to failure, fixation with the locking plate tolerated on average 20 more degrees in torsion before failure, and demonstrated higher torsional load to failure and less torsional stiffness ( P Interpretation Both locking plates and locked intramedullary nails may provide enough stability to avoid secondary displacement of proximal humerus fractures during early physical therapy. Locking plates demonstrated superior biomechanical properties under high rotational loads than locked intramedullary nails in a cadaveric proximal humerus two-part osteotomy model, and could provide more protection against unexpected high torsion loads.
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paper_title: Locking plates improve torsional resistance in the stabilization of three-part proximal humeral fractures.

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This study quantified the torsional resistance provided by locking plates and angled blade plates used to stabilize proximal humeral fractures. Three-part proximal humeral fractures were created in 6 pairs of cadaveric humeri. One specimen of each pair was reconstructed with a proximal humeral locking plate, whereas the other specimen was reconstructed with an angled blade plate. An external rotation torque, varying from 0 to 5 N-m, was applied to the humeral head until the head rotated 30 degrees or 10,000 loading cycles were applied. The mean initial torsional stiffness was significantly larger for the locking plates (0.99 N-m/degree) than for the blade plates (0.59 N-m/degree). For each pair, the maximum rotation was larger for the blade plate than for the locking plate. For this in vitro model of a reconstructed 3-part proximal humeral fracture, the locking plate provided better torsional fatigue resistance and stiffness than the blade plate.
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paper_title: Semitubular blade plate fixation in proximal humeral fractures: A biomechanical study in a cadaveric model

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This study was undertaken to compare the fixation of the semitubular blade plate with that of the AO T plate. Cadaveric humeri (n = 12 pairs) from an elderly population (41 to 89 years) had either a blade plate (n = 12) or a T plate (n = 12) fixed to them, subsequent to which a transverse osteotomy was performed. Mechanical testing in tension was performed in 1 series (n = 5, blade plate; n = 5, T plate) by applying a single maximal load to failure and in a second series (n = 7, blade plate; n = 7, T plate) by applying submaximal cyclic loading before failure was induced. Results showed that the fixation provided by the semitubular blade plate was significantly better (P <.05) than that of the T plate in those specimens subjected to submaximal cyclic loading before failure (series 2). This latter testing method contains some component of the clinical situation compared with monotonic distraction to failure. Based on these results plus favorable clinical results reported in the literature, the semitubular blade plate is possibly a better alternative to the T plate in the management of proximal humeral fractures that require open reduction and internal fixation. (J Shoulder Elbow Surg 1998;7:462-6.)
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paper_title: Biomechanical comparison of a unique locking plate versus a standard plate for internal fixation of proximal humerus fractures in a cadaveric model.

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BACKGROUND ::: Newer internal fixation devices with a locking mechanism between the plate and the screw have recently been released. The efficacy of these plates in the proximal humerus has yet to be fully described. There is a need to compare the biomechanical properties of efficacy of plate fixation with or without locking screws for surgery of two-part proximal humerus fractures. Multiple-plane locking plate and cloverleaf plate designs were tested to determine their ability to maintain fixation on the humeral head. ::: ::: ::: METHODS ::: Eight matched pairs of cadaveric shoulders with 7-millimeter osteotomy defects at the surgical neck simulating two-part fractures of the proximal humerus were loaded to failure in thirty degrees of glenohumeral abduction. One side was repaired with a proximal humerus locking plate and the other with a cloverleaf plate. The rotator cuff musculature was then loaded via a servo-hydraulic testing machine under displacement control to simulate the deforming forces present in vivo. ::: ::: ::: FINDINGS ::: The average maximum load to failure was greater in proximal humerus locking plates than in cloverleaf plates (876 versus 712; P=0.04). ::: ::: ::: INTERPRETATION ::: In the cadaveric, two-part proximal humerus fracture model that was created, the locking plate displayed significantly greater holding power of the humeral head. Clinical relevance is unproven but may be manifested in vivo as improved early range of motion exercises and functional outcome.
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paper_title: Fixed-angle plate fixation in simulated fractures of the proximal humerus: a biomechanical study of a new device.

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Abstract This study was performed to evaluate the biomechanical properties of a new device for displaced fractures of the proximal humerus. The device is a low-profile, fixed-angle plate specially designed for percutaneous application. With the use of embalmed cadaveric humeri, we simulated both noncomminuted and comminuted 2-part surgical neck fractures of the proximal humerus. Each humerus of a pair was then randomly fixed with either the new experimental device or the Association for the Study of Internal Fixation (ASIF) T-plate and mechanically tested to failure in an axial shear-loading model. The two fixation devices were evaluated in paired humeri with regard to mode of failure, stiffness, displacement at physiologic loads, and displacement, load, and energy at the point of ultimate load before failure. In the noncomminuted fracture trials the experimental device exhibited significantly greater stiffness ( P P = .002 for normalized values) and ultimate load before failure ( P = .015) and significantly less displacement at higher physiologic loads ( P = .031). In the comminuted fracture trials the experimental device exhibited significantly greater stiffness ( P = .048), ultimate load ( P P = .048) before failure, and significantly less displacement at higher ( P = .004) and lower physiologic loads ( P = .011). The study demonstrates improved biomechanical properties for the new experimental device over the T-plate in simulated fractures of the proximal humerus. We extrapolate that these improved biomechanical properties may prove advantageous in future clinical investigation.
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paper_title: Proximal Humeral Fractures: A Biomechanical Comparison of Locking Plate Constructs in a Cadaveric 3-Part Fracture Model

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The purpose of our study was to biomechanically compare, under cyclic loading conditions, fracture site motion, humeral head collapse, and intra-articular hardware penetration in simulated 3-part osteoporotic proximal humeral fractures stabilized with 1 of 2 locking-plate constructs. We performed fixation on simulated 3-part proximal humeral fractures in 10 pairs of cadaveric osteoporotic humeri with a Hand Innovations S3 Proximal Humerus Plate (S3 plate) or an LCP Proximal Humerus Plate (LCP plate; 1 each for each pair). The specimens were potted, mounted on a materials testing machine, and subjected to 5000 cycles of abduction in the scapular plane, loading through the supraspinatus tendon. Interfragmentary displacement at 2 virtual points (the most medial aspect of the calcar and the most superior aspect of the osteotomy line between the greater tuberosity and humeral head) was measured using an optical tracking system. Humeral head rotation was also measured. We used a generalized linear latent and mixed model to check for an effect of cyclic loading and treatment on the parameters of interest (significance, P < .05). After cyclic loading, the S3 plate humeri showed significantly greater displacement of the greater tuberosity fragment and rotation of the humeral head and a trend (not a significant difference) toward greater displacement at the calcar. No hardware penetration was noted for either repair. Although the S3 plate repairs resulted in significantly more fracture site motion, it is unknown whether the magnitude of the motion is clinically significant.
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paper_title: Force analysis of rotator cuff muscles.

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A 3-dimensional static biomechanical model of the glenohumeral joint was used to investigate rotator cuff muscle forces during maximal isometric exertions (abduction, adduction, internal rotation, and external rotation) and static arm elevation. Muscle moment arms and cross sectional areas were determined from studies of cadaveric specimens, and maximal isometric strength data were collected using a Cybex II dynamometer. Predicted posterior deltoid forces were very low during abduction in the scapular plane. The model predicted the highest rotator cuff muscle forces during maximal internal rotation (subscapularis) and external rotation (infraspinatus, teres minor, and supraspinatus) exertions. The results indicate that abduction exertions may not produce the greatest loads on the supraspinatus tendon, and that analyses of arm elevation may underestimate the potential loads on the rotator cuff. The strong effect of external rotation exertions on supraspinatus and infraspinatus forces suggest that ergonomic efforts to prevent rotator cuff disease should include reduction of internal rotation loading on the arm. Moreover, it may be important to include warnings about external rotation exertions, in addition to arm elevation, in patient education.
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paper_title: Fixation of three-part proximal humeral fractures: a biomechanical evaluation.

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OBJECTIVES ::: To examine the biomechanical stability of three constructs currently used for the management of three-part proximal humerus fractures. Tension band wires (TBW) with supplemental Enders nails, modified cloverleaf plate and screws, and intramedullary (IM) nailing with proximal and distal interlocks were tested to determine relative stability. ::: ::: ::: DESIGN ::: A reproducible three-part fracture was made in fresh-frozen stripped proximal humeri. The fracture was stabilized using TBW/Enders nail (n = 6), plate/screws (n = 5), or IM nailing (n = 5). ::: ::: ::: MAIN OUTCOME MEASUREMENTS ::: Mechanical testing was performed with a small preload followed by deflection of five millimeters at a rate of one millimeter per second in flexion, extension, and varus and valgus relative to the humeral shaft. A load-displacement curve was obtained. Torsional testing was performed in internal and external rotation, and torque-rotation curves were recorded. ::: ::: ::: RESULTS ::: In cantilever bending, the plate/screws construct and the IM nail construct were superior to the TBW/Enders nail construct for all parameters except extension. There was no statistically significant difference between the IM nail and the plate/screws groups. Torsional stiffness testing revealed that the plate/screws and the IM nail were superior to the TBW/Enders nail construct. There was no statistical difference between the IM nail and the plate/screws groups. ::: ::: ::: CONCLUSIONS ::: In a cadaveric model of three-part proximal humerus fractures stripped of soft tissue, plate/screws fixation and IM nailing provide greater torsional and bending stiffness than does fixation with TBW/Enders nail. There was no statistically significant difference in torsional or bending stiffness between IM nailing with interlocks and plate/screws fixation in this model.
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paper_title: Mechanisms of failure of locked-plate fixation of the proximal humerus: acoustic emissions as a novel assessment modality.

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OBJECTIVES ::: Locking plates are the predominant implants used for proximal humerus fractures. Despite a preponderance of good clinical outcomes, failures continue to occur. The purpose of this study was to investigate the failure mechanism of locked proximal humeral plate fixation and its relationship with bone density and screw length. ::: ::: ::: METHODS ::: Human cadaveric humeri were subjected to cyclic bending loads after an unstable 2-part fracture (Orthopedic Trauma Association classification 11 A-3) was created and stabilized with a locking proximal humeral plate. Acoustic emission (AE) sensors were mounted on the specimens to detect fracture displacement and generation of microcracks. The data were analyzed to evaluate construct failure. ::: ::: ::: RESULTS ::: Eight of 10 locking plate constructs in cadaver specimens failed in varus collapse. The primary influences on failure were cancellous bone density and cancellous bone screw length. AE monitoring demonstrated patterns of microcrack progression, predominantly along the inferior screws. The progression trends according to AE were similar to their respective actuator displacement versus time curves. ::: ::: ::: CONCLUSIONS ::: Cancellous bone density and total cancellous screw depth penetration seem to be critical variables. Although the patients' bone density cannot be controlled, surgeons may decrease the risk of failure by maximizing the length of the screws within the cancellous bone. Analysis of microcrack formation revealed that failures begin at the midportion and tips of the inferior screws and at the bone-plate interface of the inferior screws.
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paper_title: Biomechanical analysis of a novel locking plate with smooth pegs versus a conventional locking plate with threaded screws for proximal humerus fractures.

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BACKGROUND ::: Repair of proximal humeral fractures with locking plates has greatly improved outcomes. However, an alarming rate of complications including screw cutout and impingement under the acromion has recently been reported. A novel locking plate with smooth pegs was developed to reduce these risks. The purpose of this study was to compare these 2 fixation methods with a cadaveric biomechanical study. ::: ::: ::: MATERIALS AND METHODS ::: Fourteen pairs of cadaveric proximal humeri (mean age, 77 years) were harvested, and bone density was measured. Osteosynthesis was performed on each pair using either a locking plate with threaded screws (TS group) or smooth pegs (SP group) on the contralateral side. Seven pairs of humeri were tested for cyclic bending, and 7 pairs for cyclic torsional evaluation: TS bending, SP bending, TS torsion, and SP torsion. The bending protocol consisted of cyclically loading to a maximum of 7.5 Nm bending moment for 10,000 cycles. The torsion protocol consisted of ±2 Nm of axial torque for 10,000 cycles. Surgical neck fractures were simulated by excising a 10-mm wedge of bone. ::: ::: ::: RESULTS ::: No implant failure or screw cutout was observed in any of the groups tested. Under bending loads, mean displacement of the distal fragment was significantly less for the SP group than that for the TS group over 5,000 cycles. In torsion tests, no significant differences were observed between the 2 fixation methods. ::: ::: ::: DISCUSSION ::: The SP group demonstrated superior biomechanical characteristics to the TS group in regards to cyclic bending.
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paper_title: Medial support by fibula bone graft in angular stable plate fixation of proximal humeral fractures: an in vitro study with synthetic bone.

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BACKGROUND ::: Failure to achieve stable fixation with medial support in proximal humeral fractures can result in varus malalignment and cut-through of the proximal screws. The purpose of this study was to investigate the influence of an intramedullary fibula bone graft on the biomechanical properties of proximal humeral fractures stabilized by angular stable plate fixation in a bone model under cyclic loading. ::: ::: ::: METHODS ::: Two fixation techniques were tested in 20 composite analog humeri models. In group F- (n = 10), fractures were fixed by an anatomically formed locking plate system. In group F+ (n = 10), the same fixation system was used with an additional fibular graft model with a length of 6 cm inserted in an intramedullary manner. Active abduction was simulated for 400 cycles by use of a recently established testing setup. Fragment gap distance was measured, and thereby, intercyclic motion, fragment migration, and residual plastic deformation were determined. ::: ::: ::: RESULTS ::: The addition of a fibular graft to the fixation plate led to 5 times lower intercyclic motion, 2 times lower fragment migration, and 2 times less residual plastic deformation. Neither screw pullout, cut-through, nor implant failure was observed. ::: ::: ::: CONCLUSION ::: Medial support with an intramedullary fibular graft in an angular stable fixation of the proximal humerus in vitro increases overall stiffness of the bone-implant construct and reduces migration of the humeral head fragment. This technique might provide a useful tool in the treatment of displaced proximal humeral fractures, especially when there is medial comminution.
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paper_title: A comprehensive update on current fixation options for two-part proximal humerus fractures: a biomechanical investigation.

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BACKGROUND ::: Recent advancements in implant technology offer updated options for surgical management that have been rapidly adopted into clinical practice. The objective of this study is to biomechanically test and compare the current fixation options available for surgical fixation of two-part proximal humerus fractures and establish load to failure and stiffness values. ::: ::: ::: METHODS ::: Sixteen match-paired (32 total) fresh-frozen, cadaveric specimens were randomized to receive 1 of 4 fixation constructs following creation of an AO/OTA Type 11A3 (two-part) proximal humerus fractures. Fixation constructs tested consisted of 3.5 mm fixed angle plate (3.5-FAP), 4.5 mm fixed angle plate (4.5-FAP), humeral intramedullary nail (IMN), and a humeral intramedullary nail with a fixed angle blade (IMN-FAB). Specimen bone density was measured to ensure no adequate, non-osteoporotic bone. Constructs were tested for stiffness and ultimate load to failure and compared via one-way ANOVA analysis with subsequent post hoc Tukey HSD multiple group comparison statistical analysis. ::: ::: ::: RESULTS ::: The IMN-FAB construct was significantly stiffer than the 3.5-FAP construct (123.8 vs. 23.9, p<0.0001), the 4.5-FAP construct (123.8 vs. 33.3, p<0.0001) and the IMN construct (123.8 vs. 60.1, p=0.005). The IMN-FAB construct reported a significantly higher load to failure than the 3.5-FAB construct (4667.3 N vs. 1756.9 N, p<0.0001), and the 4.5-FAP construct (4667.3 N vs. 2829.4 N, p=0.019, Table 2). The IMN construct had a significantly higher load to failure than the 3.5-FAP construct (3946.8 vs. 1756.9, p=0.001, Table 2). ::: ::: ::: CONCLUSION ::: Biomechanical testing of modern fixation options for two-part proximal humerus fracture exhibited that the stiffest and highest load to failure construct was the IMN-FAB followed by the IMN, 3.5-FAP and then the 4.5-FAP constructs. However, prospective clinical trials with longer-term follow-up are required for definitive assessment of the ideal fixation construct for surgical management of two-part proximal humerus fractures.
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paper_title: Locked vs. unlocked plate osteosynthesis of the proximal humerus - a biomechanical study.

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BACKGROUND ::: Locked plates (internal fixators) have been found to be an optimal method for the fixation in proximal humeral fractures. In a biomechanical cadaver study the difference between locked and non-locked osteosyntheses was investigated. ::: ::: ::: METHODS ::: Paired humeri were harvested, bone density measured. Locked internal fixators were mounted on one specimen; identical plate-screw-systems without locking mechanism applied to the contralateral specimen for comparison. After that, a transverse subcapital osteotomy was performed. With 7 pairs of humeri static tests with increasing axial loads and with 5 pairs dynamic tests with 10 N preload and 80 N maximal axial load for up to 1 million cycles were performed. ::: ::: ::: RESULTS ::: In the static experiments the elastic stiffness of the construct was 74% higher in the locked group (median 80 N/mm, quartile range 77-86 N/mm) compared with the non-locked group (46 N/mm, 35.5-56.5 N/mm). The difference was statistically significant (Wilcoxon test for paired samples, P<0.05). Similarly, the linear range until failure was definitely extended in the locked group by 64% (92 N, 89-98 N vs. 56 N, 36.5-73.5 N, P<0.05). Under dynamic loading the non-locked group showed fixation failures between 97,000 and 500,000 cycles. In the locked group no failure was observed until the end of the experiment at 1 million cycles (P<0.0.5). The final deformation was found to be 1 mm (median, quartil range 1.0-1.2 mm) in the non-locked group and 0.3 mm (0.2-0.3 mm) in the locked group (P<0.05). The differences were found equally in lower as well as in higher bone density specimen. ::: ::: ::: INTERPRETATION ::: Because of the optimal load transfer between implant and cancellous bone, a locked screw plate interface will reduce fixation failure in proximal humeral fractures.
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paper_title: Biomechanical Analysis of Blade Plate Versus Locking Plate Fixation for a Proximal Humerus Fracture: Comparison Using Cadaveric and Synthetic Humeri

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Objective:To compare the mechanical stability of a fixed-angle blade plate with that of a locking plate in a cadaveric proximal humerus fracture-fixation model subjected to cyclic loading. A secondary objective was to evaluate whether the use of synthetic humerus specimens would replicate significan
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paper_title: Screw augmentation reduces motion at the bone-implant interface: a biomechanical study of locking plate fixation of proximal humeral fractures.

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BACKGROUND ::: Shear forces at the bone-implant interface lead to a loss of reduction after locking plate fixation of proximal humeral fractures. The aim of the study was to analyze the roles of medial support screws and screw augmentation in failure loads and motion at the bone-implant interface after locking plate fixation of proximal humeral fractures. ::: ::: ::: METHODS ::: Unstable 3-part fractures were simulated in 6 pairs of cadaveric humeri and were fixed with a DiPhos-H locking plate (Lima Corporate, Udine, Italy). An additional medial support screw was implanted in 1 humerus of every donor. The opposite humerus was stabilized with a medial support screw and additional bone cement augmentation of the 2 anteriorly directed head screws. Specimens were loaded in the varus bending position. Stiffness, failure loads, plate bending, and the motion at the bone-implant interface were evaluated using an optical motion capture system. ::: ::: ::: RESULTS ::: The mean load to failure was 669 N (standard deviation [SD], 117 N) after fixation with medial support screws alone and 706 N (SD, 153 N) after additional head screw augmentation (P = .646). The initial stiffness was 453 N/mm (SD, 4.16 N/mm) and 461 N/mm (SD, 64.3 N/mm), respectively (P = .594). Plate bending did not differ between the 2 groups. However, motion at the bone-implant interface was significantly reduced after head screw augmentation (P < .05). ::: ::: ::: CONCLUSION ::: The addition of bone cement to augment anteriorly directed head screws does not increase stiffness and failure loads but reduces motion at the bone-implant interface. Thus, the risk of secondary dislocation of the head fragment may be reduced.
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paper_title: In vivo measurement of shoulder joint loads during activities of daily living.

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Until recently the contact loads acting in the glenohumeral joint have been calculated using musculoskeletal models or measured in vitro. Now, contact forces and moments are measured in vivo using telemeterized shoulder implants. Mean total contact forces from four patients during eight activities of daily living are reported here. Lifting a coffee pot (1.5kg) with straight arm caused an average force of 105.0%BW (%body weight) (range: 90-124.6%BW), while setting down the coffee pot in the same position led to higher forces of 122.9%BW on the average (105.3-153.4%BW). The highest joint contact forces were measured when the straight arm was abducted or elevated by 90 degrees or more, with a weight in the hand. Lifting up 2kg from a board up to head height caused a contact force of 98.3%BW (93-103.6%BW); again, setting it down on the board led to higher forces of 131.5%BW (118.8-144.1%BW). In contrast to previously calculated high loads, the contact force during passive holding of a 10kg weight laterally was only 12.3%BW (9.2-17.9%BW), but when lifting it up to belt height it increased to 91.5%BW (87-95%BW). The moments transferred inside the joint at our patients varied much more than did the forces both inter and intra-individually. Our data suggest that patients with shoulder problems or during the first post-operative weeks after shoulder fractures or joint replacements should avoid certain activities encountered during daily living e.g. lifting or holding a weight with an outstretched arm. Some energy-related optimization criteria used in the literature for analytical musculoskeletal shoulder models must now be reconsidered.
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paper_title: Proximal humeral fracture fixation: a biomechanical comparison of two constructs.

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BACKGROUND ::: Different options exist for stabilizing proximal humeral fractures. This study compared the mechanical stability of 2 common proximal humeral fixation plates in bending and torsion. ::: ::: ::: METHODS ::: Tests were conducted on 40 synthetic and 10 matched pairs of cadaveric humeri (evenly fixed with DePuy S3 proximal humeral plating system [DePuy Orthopaedics, Warsaw, IN, USA] and Synthes proximal humerus locking compression plate [Synthes, Paoli, PA, USA]). Half of the humeri were tested by cantilevered bending in flexion, extension, varus, and valgus for 100 cycles of ±5 mm of displacement at 1 mm/s before loading to failure in varus. The other half were tested in torsion for 100 cycles of ±8° of rotational displacement at 1°/s before loading to failure in external rotation. ::: ::: ::: RESULTS ::: Peak cyclic loads for synthetic constructs were higher for DePuy plates than Synthes plates in varus and valgus (P < .0001), but a difference was not detected in extension (P > .40) or flexion (P = .0675). Peak cyclic loads for cadaveric constructs showed a significant difference in extension and flexion (Synthes > DePuy, P < .0001) and in varus (DePuy > Synthes, P < .05) but not in valgus (P > .10). Bending stiffness during varus failure testing was higher for DePuy plates than Synthes plates (P < .0001) for synthetic constructs. Regarding torsion of synthetic and cadaveric constructs, DePuy plates experienced higher peak cyclic torques over all cycles in both directions (P < .0001). For synthetic constructs, DePuy plates showed higher torsional stiffness in external failure than Synthes plates (P < .0001). ::: ::: ::: CONCLUSIONS ::: The DePuy plate was stiffer than the Synthes plate with varus and valgus bending, as well as in torsion. The Synthes plate tended to be stiffer in flexion and extension.
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paper_title: Inertia and muscle contraction parameters for musculoskeletal modelling of the shoulder mechanism.

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To develop a musculoskeletal model of the shoulder mechanism, both shoulders of seven cadavers were measured to obtain a complete set of parameters. Using antropometric measurements, the mass and rotational inertia of segments were estimated, followed by three-dimensional measurements of all morphological structures relevant for modelling, i.e. muscle origins and insertions, muscle bundle directions, ligament attachments and articular surfaces; all in relation to selected bony landmarks. Subsequently, muscle contraction parameters as muscle mass and physiological cross-sectional area were measured. The method of data collection and the results for inertia and muscle contraction parameters as prerequisities for modelling are described.
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paper_title: Forces at the Glenohumeral Joint in Abduction

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The purpose of this study was to determine the forces in the glenohumeral joint for isometric abduction (including all directions of rotation) in the plane of the scapula. The lines of actions of muscles were obtained from 3 upper quarter specimens, electromyographic data was used, as well as geometrical parameters of shoulder motion. The main assumption made in the analysis was that the force in a muscle was proportional to its area times the integrated electromyographic signal. The resultant force reached a maximum of 0.89 times body weight at 90 degrees of abduction, while the shearing component up the face of the glenoid was a maximum of 0.42 times body weight at 60 degrees of abduction.
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paper_title: The Biomechanics of Locked Plating for Repairing Proximal Humerus Fractures With or Without Medial Cortical Support

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Background:Comminuted proximal humerus fracture fixation is controversial. Locked plate complications have been addressed by anatomic reduction or medial cortical support. The relative mechanical contributions of varus malalignment and lack of medial cortical support are presently assessed.Methods:F
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paper_title: Intramedullary cortical bone strut improves the cyclic stability of osteoporotic proximal humeral fractures

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Proximal humeral fractures treated with locking plate can fail due to varus collapse, especially in osteoporotic bone with medial cortex comminution. The use of an intramedullary strut together with locking plate fixation may strengthen fixation and provide additional medial support to prevent the varus malalignment. This study biomechanically investigates the influence of an intramedullary cortical bone strut on the cyclic stability of proximal humeral fractures stabilized by locking plate fixation in a cadaver model. Ten cadaveric humeri were divided into two groups statistically matched for bone density. Each specimen was osteotomized with 10 mm gap at the surgical neck. The non-augmented group stabilized with locking plate alone; in the augmented group, a locking plate was used combined with an intramedullary cortical bone strut. The strut was retrograded into the subchondral bone, and three humeral head screws were inserted into the strut to form a plate-screw-strut mechanism. The cyclic axial load was performed to 450 N for 6000 cycles and then loaded to failure. Construct stiffness, cyclic loading behavior and failure strength were analyzed to identify differences between groups. The augmented constructs were significantly stiffer than the non-augmented constructs during cycling. On average, the maximum displacements at 6000 cycles for non-augmented and augmented groups were 3.10 ± 0.75 mm and 1.7 ± 0.65 mm (p = 0.01), respectively. The mean peak-to-peak (inter cycle) displacement at 6000 cycles was about 2 times lower for the augmented group (1.36 ± 0.68 mm vs. 2.86 ± 0.51 mm). All specimens showed varus collapse combined with loss of screw fixation of the humeral head. The failure load of the augmented group was increased by 2.0 (SD = 0.41) times compared with the non-augmented group (p < 0.001). The stability and strength of the locking plate augmented with an intramedullary strut were significantly increased. For bone with poor quality, the subsidence of the locked screws led larger displacement, decreased the stability of the constructs, however, the plate-screw-strut mechanism provided more rigidity to stabilize the fixation. This study emphasized the importance of intramedullary support for the proximal humeral fractures fixed with a locked plate under cyclic loading, especially in bone with poor quality. This work is based on the results of cadaver model, further in vivo analysis is necessary to determine if the clinical results can be extrapolated from this data.
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paper_title: Proximal humeral fractures: what is semi-rigid? Biomechanical properties of semi-rigid implants, a biomechanical cadaver based evaluation

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INTRODUCTION ::: Proximal humerus fractures remain challenging especially in the elderly. Biomechanical data put semi-rigid implants in favour of osteopenic or osteoporotic situation. Little surgical side damage is associated with a minimal invasive approach of these implants. The aim of this study was to evaluate the mechanical properties of three such implants. ::: ::: ::: MATERIAL AND METHODS ::: Fresh frozen cadaver specimens were mounted as proposed by the distributors. Three different implants were used: LCP-PH (locking compression plate proximal humerus, Synthes, Austria), HB (humerus block, Synthes, Austria), and IMC (intramedullary claw, ITS, Austria). Subcapital fracture was simulated by resecting a 5 mm gap. All specimens were comparable in "B" (one), "M" (ineral) and "D" (ensity). Four load cases were tested: varus bending, medial shearing and axial torque. A cyclic test (1,000 cycles) was performed in the first load case (varus stress) for all three implants. ::: ::: ::: RESULTS ::: The LCP-PH was the most rigid in all three load cases, always followed by the HB. The IMC was the most elastic device with almost immeasurable values in axial torque. In the cyclic setting, the load reduction of the HB followed by the LCP-PH was significantly better than that for the IMC. ::: ::: ::: CONCLUSION ::: The differences in stiffness are varying tremendously. The IMC is the implant with the lowest stiffness in all load cases and the highest load reduction. New "semi-rigids" claim good clinical performance, yet prospective clinical studies have to prove this. It is unlikely that the IMC can maintain fracture reduction in fracture situations of complex nature (no ligamentotaxis).
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paper_title: In vivo gleno-humeral joint loads during forward flexion and abduction.

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To improve design and preclinical test scenarios of shoulder joint implants as well as computer-based musculoskeletal models, a precise knowledge of realistic loads acting in vivo is necessary. Such data are also helpful to optimize physiotherapy after joint replacement and fractures. This is the first study that presents forces and moments measured in vivo in the gleno-humeral joint of 6 patients during forward flexion and abduction of the straight arm. The peak forces and, even more, the maximum moments varied inter-individually to a considerable extent. Forces of up to 238%BW (percent of body weight) and moments up to 1.74%BWm were determined. For elevation angles of less than 90° the forces agreed with many previous model-based calculations. At higher elevation angles, however, the measured loads still rose in contrast to the analytical results. When the exercises were performed at a higher speed, the peak forces decreased. The force directions relative to the humerus remained quite constant throughout the whole motion. Large moments in the joint indicate that friction in shoulder implants is high if the glenoid is not replaced. A friction coefficient of 0.1–0.2 seems to be realistic in these cases.
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paper_title: Biomechanical in vitro assessment of screw augmentation in locked plating of proximal humerus fractures

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Abstract Introduction Proximal humerus fracture fixation can be difficult because of osteoporosis making it difficult to achieve stable implant anchorage in the weak bone stock even when using locking plates. This may cause implant failure requiring revision surgery. Cement augmentation has, in principle, been shown to improve stability. The aim of this study was to investigate whether augmentation of particular screws of a locking plate aimed at a region of low bone quality is effective in improving stability in a proximal humerus fracture model. Materials and methods Twelve paired human humerus specimens were included. Quantitative computed tomography was performed to determine bone mineral density (BMD). Local bone quality in the direction of the six proximal screws of a standard locking plate (PHILOS, Synthes) was assessed using mechanical means (DensiProbe™). A three-part fracture model with a metaphyseal defect was simulated and fixed with the plate. Within each pair of humeri the two screws aimed at the region of the lowest bone quality according to the DensiProbe™ were augmented in a randomised manner. For augmentation, 0.5 ml of bone cement was injected in a screw with multiple outlets at its tip under fluoroscopic control. A cyclic varus-bending test with increasing upper load magnitude was performed until failure of the screw–bone fixation. Results The augmented group withstood significantly more load cycles. The correlation of BMD with load cycles until failure and BMD with paired difference in load cycles to failure showed that augmentation could compensate for a low BMD. Discussion and conclusion The results demonstrate that augmentation of screws in locked plating in a proximal humerus fracture model is effective in improving primary stability in a cyclic varus-bending test. The augmentation of two particular screws aimed at a region of low bone quality within the humeral head was almost as effective as four screws with twice the amount of bone cement. Screw augmentation combined with a knowledge of the local bone quality could be more effective in enhancing the primary stability of a proximal humerus locking plate because the effect of augmentation can be exploited more effectively limiting it to the degree required.
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paper_title: Biomechanical in vitro assessment of fixed angle plating using a new concept of locking for the treatment of osteoporotic proximal humerus fractures

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Locked plating attempts to improve mechanical stability via better anchorage of the screws in the bone. In 22 paired osteoporotic humeri an AO/ASIF 11-B 1 fracture was created. Locked and conventional plating using the same device of the latest generation was performed. Torsional loading around three axes (x = varus/valgus, y = flexion/extension, z = axial rotation) with an increasing moment (2, 3.5, 5 and 7.5 N·m) was applied. Interfragmentary motion within the locked group was lower for all three axes with higher cumulative survival rates (p < 0.05). The typical mode of failure was loss of fixation in the humeral head occurring earlier in the conventional group. The locking mechanism investigated provides more ultimate strength in an osteoporotic proximal humerus fracture model. Correlation with BMD suggests that this device may especially be suitable for use in osteoporotic bone.
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paper_title: Biomechanical comparison of a proximal humeral locking plate using two methods of head fixation.

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HYPOTHESIS ::: Locking plates have emerged as the implant of choice for stabilization of proximal humeral fractures. The biomechanical properties of a locked plating system using smooth pegs vs threaded screws for fixation of the humeral head were compared to test the hypothesis that there would be no biomechanical difference between pegs and threaded screws. ::: ::: ::: MATERIALS AND METHODS ::: Sixteen pairs of fresh frozen cadaveric humeri were randomized to have a surgical neck gap osteotomy stabilized with a locked plate using threaded screws (n=8) or smooth pegs (n=8). The intact contralateral humerus served as a control. Each specimen was tested with simultaneous cyclic axial compression (40 Nm) and torsion (both +/-2 Nm and +/-5 Nm) for 6000 cycles. All specimens were loaded to failure. Interfragmentary motion and load-displacement curves were analyzed to identify differences between the groups. Our data were then compared to previously published forces across the glenohumeral joint to provide evidence based recommendations for postoperative use of the shoulder. ::: ::: ::: RESULTS ::: There was a statistically significant difference between test specimens and their paired control (P < .001) in cyclic testing and load to failure. Differences between the smooth pegs and threaded screws were not statistically significant. ::: ::: ::: DISCUSSION ::: There is no biomechanical difference between locked smooth pegs and locked threaded screws for proximal fragment fixation in an unstable 2-part proximal humeral fracture model. ::: ::: ::: CONCLUSION ::: Our study contributes to the published evidence evaluating forces across the glenohumeral joint and suggests that early use of the affected extremity for simple activities of daily living may be safe. Use of the arm for assisted ambulation requiring a crutch, cane, walker, or wheelchair should be determined on a case-by-case basis.
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paper_title: Influence of plate material and screw design on stiffness and ultimate load of locked plating in osteoporotic proximal humeral fractures

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Abstract Introduction The main purpose was to compare the biomechanical properties of a carbon-fibre reinforced polyetheretherketone (CF-PEEK) composite locking plate with pre-existing data of a titanium-alloy plate when used for fixation of an unstable 2-part fracture of the surgical neck of the humerus. The secondary purpose was to compare the mechanical behaviour of locking bolts and conventional locking cancellous screws. Methods 7 pairs of fresh frozen human humeri were allocated to two equal groups. All specimens were fixed with the CF-PEEK plate. Cancellous screws (PEEK/screw) were compared to locking bolts (PEEK/bolt) for humeral head fixation. Stiffness, fracture gap deflection and ultimate load as well as load before screw perforation of the articular surface were assessed. Results were compared between groups and with pre-existing biomechanical data of a titanium-alloy plate. Results The CF-PEEK plate featured significantly lower stiffness compared to the titanium-alloy plate ( P P > 0.05). Discussion The CF-PEEK plate has more elastic properties and significantly increases movement at the fracture site of an unstable proximal humeral fracture model compared to the commonly used titanium-alloy plate. The screw design however does neither affect the constructs primary mechanical behaviour in the constellation tested nor the load before screw perforation.
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paper_title: Simulated joint and muscle forces in reversed and anatomic shoulder prostheses

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Reversed shoulder prostheses are increasingly being used for the treatment of glenohumeral arthropathy associated with a deficient rotator cuff. These non-anatomical implants attempt to balance the joint forces by means of a semi-constrained articular surface and a medialised centre of rotation. A finite element model was used to compare a reversed prosthesis with an anatomical implant. Active abduction was simulated from 0° to 150° of elevation. With the anatomical prosthesis, the joint force almost reached the equivalence of body weight. The joint force was half this for the reversed prosthesis. The direction of force was much more vertically aligned for the reverse prosthesis, in the first 90° of abduction. With the reversed prosthesis, abduction was possible without rotator cuff muscles and required 20% less deltoid force to achieve it. This force analysis confirms the potential mechanical advantage of reversed prostheses when rotator cuff muscles are deficient.
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paper_title: Biomechanical comparison of an angular stable plate with augmented and non-augmented screws in a newly developed shoulder test bench.

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BACKGROUND ::: The proximal humeral fracture is one of the most common fractures. Although there are a number of treatment options available, the clinical outcomes in geriatric patients are still unsatisfactory. Therefore, the aim of this study was to investigate the biomechanical behaviour of an angular stable plate with either augmented or non-augmented screws using two different fracture models in a shoulder test bench with active muscle forces. ::: ::: ::: METHODS ::: Six paired fresh-frozen humeri were loaded into a shoulder test bench simulating ab- and adduction between 15 and 45° induced by active muscle forces. The bone mineral density was measured by a quantitative CT. A two-part fracture model (stable and an unstable) was used to investigate the different biomechanical behaviours of the PHILOS plate, either utilising cannulated screws, allowing in situ augmentation, or without utilising augmented screws. Four screws were augmented with 0.5ml PMMA cement. ::: ::: ::: FINDINGS ::: The in vitro-measured resulting forces in the glenoid fossa were comparable to the in vivo forces generated in shoulder arthroplasties. Under stable conditions, the per cycle motion and varus impaction tilting showed no significant difference. In the unstable state, the augmented group showed a maximum of 0.81° per cycle motion and a maximum varus impaction of -1.46° compared to the non-augmented maximum of 2.31° per cycle motion and maximum varus impaction of -4.26° (P<0.05). ::: ::: ::: INTERPRETATION ::: In an unstable fracture model under dynamic testing conditions, augmentation leads to a decreased per cycle motion and varus impaction of the humeral head.
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paper_title: A mechanical comparison between conventional and modified angular plates for proximal humeral fractures.

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The objective of this study is to present a modified angular blade plate for fixing 2-part and even 3-part fractures of the proximal humerus, as well as the results of the comparative mechanical test between the conventional angular blade plate and this new modified plate. The plates were tested in flexion and rotational trials in a wooden model that simulated a 2-part humeral fracture of the proximal extremity. The results (mean +/- SD) of bending strength and stiffness obtained after testing showed findings of 601 +/- 349 N and 0.5 +/- 0.2 N/mm, respectively, for the conventional plate and 4005 +/- 164 N and 3.9 +/- 0.7 N/mm, respectively, for the modified plate. The torsional stiffness test showed findings of 1.26 +/- 0.09 KN.mm degrees for the conventional plate and 1.74 +/- 0.21 KN.mm degrees for the modified plate. The test of torsional moment showed findings of 57.0 +/- 7.6 KN.mm for the conventional plate and 115.2 +/- 9.3 KN.mm for the modified plate. The test of angular displacement at the torsional moment showed findings of 50.8 degrees +/- 7.2 degrees for the conventional plate and 70.2 degrees +/- 2.6 degrees for the modified plate. The results of the mechanical trials of flexion and rotation were superior for the modified angular blade plate compared with the conventional angular blade plate.
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paper_title: BIOMECHANICAL EVALUATION OF PROXIMAL HUMERAL FRACTURE FIXATION SUPPLEMENTED WITH CALCIUM PHOSPHATE CEMENT

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Background: Proximal humeral fractures are common injuries, and numerous surgical methods have been described for their treatment. The biomechanical characteristics of various internal fixation devices that are used to treat these fractures have not been extensively studied, nor has the potential beneficial effect of calcium phosphate cement supplementation. Methods: We used a cadaveric three-part proximal humeral osteotomy model to perform a biomechanical evaluation of three types of internal fixation devices: a cloverleaf plate, an angled blade-plate, and Kirschner wires. The effect of supplementing the fixation with SRS (Skeletal Repair System) calcium phosphate cement was evaluated as well. Eighteen pairs of fresh-frozen humeri were obtained, and the bone-mineral density of each specimen was measured. In each pair, one specimen was secured with internal fixation alone and the contralateral specimen was secured with internal fixation combined with calcium phosphate cement. The specimens were tested cyclically in abduction and in external rotation for 250 cycles to evaluate interfragmentary motion. The specimens were then loaded to failure in external rotation to measure torsional load to failure and torsional stiffness. Results: Overall, there were no significant differences between the specimens treated with the blade and cloverleaf plates, whereas the specimens treated with Kirschner wires demonstrated more interfragmentary motion, less stiffness, and lower torque to failure. In general, supplementation with calcium phosphate cement led to significant improvements in the mechanical performance of all three forms of internal fixation as demonstrated by a significant decrease in interfragmentary motion, a significant increase in torque to failure, and a significant increase in torsional stiffness. The addition of calcium phosphate cement increased the stiffness of even the most osteoporotic specimens to levels that were higher than those of the most osteodense specimens that had been treated with internal fixation alone. Conclusion: The initial biomechanical properties of internal fixation as measured with use of a proximal humeral osteotomy model and three methods of fixation were significantly improved by the addition of calcium phosphate cement. Clinical Relevance: The addition of calcium phosphate cement may augment the mechanical characteristics of internal fixation of difficult, three-part proximal humeral fractures. The ability to stabilize the interface between the implant and cancellous bone, particularly in the presence of osteopenia, may make calcium phosphate cement a valuable clinical tool in the treatment of these difficult fractures.
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paper_title: The effect of in situ augmentation on implant anchorage in proximal humeral head fractures

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Abstract Introduction Fracture fixation in patients suffering from osteoporosis is difficult as sufficient implant anchorage is not always possible. One method to enhance implant anchorage is implant/screw augmentation with PMMA-cement. The present study investigated the feasibility of implant augmentation with PMMA-cement to enhance implant anchorage in the proximal humerus. Materials and methods A simulated three part humeral head fracture was stabilised with an angular stable plating system in 12 pairs of humeri using six head screws. In the augmentation group the proximal four screws were treated with four cannulated screws, each augmented with 0.5 ml of PMMA-cement, whereas the contra lateral side served as a non-augmented control. Specimens were loaded in varus-bending or axial-rotation using a cyclic loading protocol with increasing load magnitude until failure of the osteosynthesis occurred. Results Augmented specimens showed a significant higher number of load cycles until failure than non-augment specimens (varus-bending: 8516 (SD 951.6) vs. 5583 (SD 2273.6), P = 0.014; axial-rotation: 3316 (SD 348.8) vs. 2050 (SD 656.5), P = 0.003). Non-augmented specimens showed a positive correlation of load cycles until failure and measured bone mineral density (varus-bending: r = 0.893, P = 0.016; axial-rotation: r = 0.753, P = 0.084), whereas no correlation was present in augmented specimens (varus-bending: r = 0,258, P = 0.621; axial-rotation r = 0.127, P = 0.810). Conclusion These findings suggest that augmentation of cannulated screws is a feasible method to enhance implant/screw anchorage in the humeral head. The improvement of screw purchase is increasing with decreasing bone mineral density.
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paper_title: Biomechanical evaluation of locked plating in proximal humeral fractures

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The ideal method of fixation in proximal humeral fractures is not well established. Locked plating is a potential solution, but to date, there has been little support shown in the literature. We compared the biomechanical performance of a locked plate with that of an intramedullary humeral nail in a cadaveric model. Paired fresh-frozen cadaveric humeri (N = 5) were instrumented with either a locked plate or an intramedullary nail after creation of a 3-part osteotomy. Construct stiffness, cyclic loading behavior, and load to failure were evaluated. The locked plate was more stiff in valgus loading than the nail (P = .003). All other loading vectors showed no statistical differences in stiffness between the two constructs. The load to failure was 828 N for the plate and 901 N for the nail. The nail showed interfragmentary motion (degrees), or toggle, at zero load, whereas the plate did not. The locked plate, being stable at zero load, may prove useful in earlier pain-free rehabilitation of proximal humeral fractures.
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paper_title: Proximal humeral fracture fixation: locking plate construct ± intramedullary fibular allograft.

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BACKGROUND ::: Locking plate constructs for proximal humeral fractures can fail due to varus collapse, especially in osteoporotic bone with medial cortex comminution. Augmentation, using a fibular allograft as an intramedullary bone peg, may strengthen fixation preventing varus collapse. This study investigated the ability of the augmented locking plate construct to withstand repetitive varus stresses relative to the nonaugmented construct. ::: ::: ::: MATERIALS AND METHODS ::: Proximal humeral fractures with medial comminution were simulated by performing wedge-shaped osteotomies at the surgical neck in cadaveric specimens. For each cadaver (n = 8), 1 humeral fracture was fixated with the locking plate construct alone and the other with the locking plate construct plus ipsilateral fibular autograft augmentation. The humeral head was immobilized and a repetitive, medially directed load was applied to the humeral shaft until construct collapse or until 25000 cycles were completed. ::: ::: ::: RESULTS ::: No augmented construct collapsed. In comparison, 6 of 8 nonaugmented constructs collapsed (P < .05). Collapse in the 6 nonaugmented constructs occurred after an average ±SD of 6604 ± 1984 cycles. Screw penetration of the articular surface was found in only 1 of the nonaugmented constructs. ::: ::: ::: CONCLUSION ::: Fibular allograft augmentation increased the ability of the locking plate to withstand repetitive varus loading. Clinically, this may assist proximal humeral fracture fixation in osteoporotic bone with medial cortex comminution.
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paper_title: PEEK versus titanium locking plates for proximal humerus fracture fixation: a comparative biomechanical study in two- and three-part fractures

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Introduction ::: The high rigidity of metal implants may be a cause of failure after fixation of proximal humerus fractures. Carbon fiber-reinforced polyetheretherketone (PEEK) plates with a modulus similar to human cortical bone may help to overcome this problem. The present study assesses the biomechanical behavior of a PEEK plate compared with a titanium locking plate.
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paper_title: Monoaxial versus polyaxial locking systems: a biomechanical analysis of different locking systems for the fixation of proximal humeral fractures

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Objective ::: The development of locking plate systems has led to polyaxial screws and new plate designs. This study compares monoaxial head locking screws (PHILOS© by Synthes) and a new generation of polyaxial locking screws (NCB-LE© by Zimmer) with respect to biomechanical stability.
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paper_title: The Humerusblock NG: a new concept for stabilization of proximal humeral fractures and its biomechanical evaluation

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Background ::: The Humerusblock NG represents a new semi-rigid angular stable fixation device for minimally invasive stabilization of proximal humeral fractures. This study evaluates the function and stability of the Humerusblock NG and its biomechanical properties on the basis of two different fracture models under cyclic loading.
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paper_title: No Contribution of Tension-Reducing Rotator Cuff Sutures on Locking Plate Fixation in a 2-Part Proximal Humerus Fracture Model.

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OBJECTIVES ::: Varus failure is a well-known complication of open reduction internal fixation of proximal humeral fractures. The addition of tension-reducing sutures from the plate to the rotator cuff may attenuate the deforming forces of the rotator cuff resulting in decreased varus failure. In this study, we investigate the biomechanical contributions of tension-reducing sutures to a locked plate construct in a 2-part proximal humerus fracture model. ::: ::: ::: METHODS ::: Two fixation techniques were tested in 12 matched fresh frozen humeri in which standard 2-part fractures of the surgical neck were created with a gap simulating surgical neck medial comminution. In group 1, fractures were fixed with a standard proximal humerus locking plate. In group 2, the plate fixation was similar, and additionally, tension-reducing sutures were applied from the plate to the rotator cuff. Active abduction was simulated for 400 cycles with force applied through the rotator cuff tendons. Intercyclic fracture motion, change in displacement, and load to failure were recorded. ::: ::: ::: RESULTS ::: The addition of tension-reducing sutures did not lead to significant differences in intercyclic fracture motion. The mean change in displacement and load to failure were similar in both groups. Failure typically occurred in both groups at the rotator cuff testing clamp interface. ::: ::: ::: CONCLUSIONS ::: Tension-relieving rotator cuff sutures added to locking plate fixation did not lead to a change in fracture gap with cyclic loading or an increase in ultimate failure load in a 2-part surgical neck proximal humerus fracture model without medial support.
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paper_title: How does a varus deformity of the humeral head affect elevation forces and shoulder function? A biomechanical study with human shoulder specimens.

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OBJECTIVES ::: A biomechanical study was performed to test the hypothesis that a varus deformity of the humeral head decreases supraspinatus (SSP) efficiency and increases deltoid elevation forces in human specimens. ::: ::: ::: METHODS ::: Twenty-four fresh-frozen human shoulder specimens were prepared by preserving the rotator cuff and deltoid. A defined, medial closed-wedge osteotomy was performed and lateral locked plate applied to simulate a varus deformity of 45° in Group I (n = 8) and 20° in Group II (n = 8). The control group (n = 8) was not osteotomized. The effect of the deformities on arm elevation forces was measured in a robot-assisted shoulder simulator under a physiologically loaded rotator cuff during three elevation phases. Phase 1 encompassed 0° to 30°, Phase 2 was from 30° to 60°, and Phase 3 included 60° to 90° of shoulder elevation. ::: ::: ::: RESULTS ::: SSP efficiency, defined as the degree of elevation attained per unit muscle force, was significantly less in Group I compared with Group II (P = 0.036) and the control group (P = 0.039) (Group I = 0.12 ± 0.03°/N, Group II 0.18 ± 0.05°/N, and control group 0.24 ± 0.10°/N). Under physiological loading of the rotator cuff, the deltoid (DELT) elevation forces were significantly greater in Group I (Pphase 1 = 0.015, Pphase 3 = 0.001) and Group II (Pphase 1 = 0.015, Pphase 3 = 0.006) compared with the control group in elevation Phase 1 (Group I: 3.20 ± 1.04 N/°, Group II: 3.03 ± 0.96 N/°, control group: 2.01 ± 0.53 N/°) and Phase 3 (Group I: 2.50 ± 0.85 N/°, Group II: 1.55 ± 0.28 N/°, control group: 1.21 ± 0.18 N/°). When the SSP was unloaded, the DELT elevation forces were significantly greater in Group l than in Group II (P = 0.040) and the control group (P = 0.004) during elevation Phase 3 (Group I: 2.12 ± 0.60 N/°, Group II: 1.47 ± 0.34 N/°, control group: 1.24 ± 0.32 N/°). ::: ::: ::: CONCLUSIONS ::: A varus deformity of the humeral head changes the pretension of the rotator cuff and results in a significantly decreased SSP efficiency (45° varus) and significantly higher arm elevation forces (20° varus). Clinically, the study's findings are relevant because they indicate that varus deformities of more than 20° should not be accepted intraoperatively and might indicate the need for surgical correction in case of subsequent symptoms.
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paper_title: Biomechanical effects of calcar screws and bone block augmentation on medial support in locked plating of proximal humeral fractures

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Abstract Background The objective of this study was to investigate the biomechanical effects of medial fracture gap augmentation in locked plating of an unstable 2-part proximal humeral fracture with calcar screws and insertion of a corticocancellous bone block. Furthermore the mechanical behavior of dynamic locking screws in the non-parallel arrangement of a proximal humeral plate was of interest. Methods Thirty-two fresh frozen humeri were randomized in four equal groups. An unstable 2-part fracture was fixed by locked plating in all specimens. The basic screw setup was supplemented by additional calcar screws in one group. Humeral head screws were replaced by dynamic locking screws in a second group. The third group featured an additional corticocancellous femoral head allograft. Assessment of stiffness was followed by cyclic loading and load to failure tests. Resulting stiffness, fracture gap deflection and ultimate load were compared utilizing Bonferroni corrected t-test for independent samples. Findings The mechanical effect of additional calcar screws was non-significant as compared to the basic screw configuration whereas bone block insertion significantly increased construct stiffness and failure load. The use of dynamic locking screws did not significantly reduce construct stiffness when compared to conventional locking screws. Interpretation Additional calcar screws alone did not improve the initial biomechanical properties of an unstable 2-part proximal humeral fracture model. However bone block augmentation appeared to be a reliable alternative of additional bony support by raising stiffness and failure load. Dynamic locking screws did not show their expected dynamic component when used in a non-parallel arrangement.
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paper_title: Straining of the intact and fractured proximal humerus under physiological-like loading.

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Surgical treatment of proximal humeral fractures remains challenging in elderly patients, primarily due to insufficient implant fixation. Both bone quality and physiological-like loading conditions are commonly overlooked during pre-clinical in vitro evaluation. However, this knowledge is necessary in order to improve surgical treatment of the proximal humerus and the mechanical behavior of implants, particularly in patients with complex fractures and weak bone stock. We hypothesize that the bone quality has a high influence on the bone straining, independent of the arm position. The goal of this study was to determine the straining of the intact and fractured proximal humerus under physiological-like loading conditions. Furthermore, the impact of augmentation on tissue straining was evaluated. Two representative humeri were selected for this study, one osteoporotic and one reference quality, and scanned using both QCT and DEXA (average DEXA value=0.26 and 0.49 g/cm2 respectively). Subcaptial defects were generated, then stabilized with a plate prior to mechanical stiffness testing. From the QCT data, finite element models were generated and the in vitro stiffness tests analytically simulated. Under physiological-like loading conditions, the straining of the bone and implant were analyzed for 0 degrees, 90 degrees forward flexion, and 90 degrees abduction. Maximal strain values were found for the intact and fractured bone at 90 degrees abduction. This study demonstrates that the straining in a fractured bone of poor quality leads to considerably higher bone strains (up to +30%) than in a more healthy bone. Augmentation of a central void under physiological-like loading with commercial cement led to mechanical failure at the bone-cement interface. New concepts for the surgical treatment of complex fractures of the proximal humerus should take bone distribution into account and thereby allow effective treatment of fractures in osteoporotic patients. The ultimate salvage procedure of augmentation has mechanical limitations as long as current cement materials are used in osteoporotic patients.
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paper_title: Biomechanical Evaluation of Locking Plate Fixation of Proximal Humeral Fractures Augmented With Calcium Phosphate Cement

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OBJECTIVES ::: To evaluate the influence of calcium phosphate cement augmentation on failure of locking plate fixation of proximal humeral fracture fixation in a cadaveric fracture model. ::: ::: ::: METHODS ::: A 5-mm wedge osteotomy was created in each of 11 paired fresh-frozen human cadaveric humeri (age > 65 years). Specimens were randomly assigned to receive either locked plate fixation (group 1) or locked plate fixation with cement augmentation (group 2). Constructs were tested for axial stiffness, load to failure, and failure mode using a material testing machine. ::: ::: ::: RESULTS ::: Cement-augmented specimens resisted higher loads (1936 ± 609 N) in comparison to nonaugmented specimens (1373 ± 590 N) (P = 0.01). In group 1, varus displacement and glenohumeral screw perforation occurred in all cases. Varus displacement occurred in 2 cases in group 2, whereas glenohumeral screw perforation did not occur in any of the cases. Cement augmentation led to a significant increase in axial stiffness (P = 0.04). ::: ::: ::: CONCLUSIONS ::: Calcium phosphate cement-augmented locking plates enhanced fixation stability in proximal humeral fractures and reduced glenohumeral screw perforation in this 2-part cadaveric model. The ultimate advantage of this method remains to be determined in vivo.
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paper_title: 45. BIOMECHANICAL ANALYSIS OF PROXIMAL HUMERAL FIXATION USING LOCKING PLATE FIXATION WITH AN INTRAMEDULLARY FIBULAR ALLOGRAFT

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Purpose: The purpose of this study is to compare two fixation methods for surgical neck proximal humeral fractures with medial calcar comminution: locking plate fixation alone and locking plate fixation with intramedullary allograft fibular bone peg augmentation. Method: Eight embalmed pairs of cadaveric specimens were utilized in this study. Dual energy X-ray absorptiometry (DXA) scans were initially performed to determine the bone density of the specimens. Surgical neck proximal humerus fractures were simulated in these specimens by creating a 1-centimeter wedge-shaped osteotomy at the level of the surgical neck to simulate medial calcar fracture comminution. Each pair of specimens had one arm randomly repaired with locking plate fixation, and the other arm repaired with locking plate fixation augmented with an intramedullary fibular autograft bone peg. The constructs were tested in bending to determine the failure loads, and initial stiffness using Digital Imaging Correlation (DIC) technology. The moment created by the rotator cuff was replicated by fixating the humeral head, and applying a point load to the distal humerus. A load was applied with a displacement rate of 4 mm/min, and was stopped approximately every 5 lbs to take a picture and record the load. This process was continued until failure of the specimens was obtained. Results: The intramedullary bone peg autograft increased the failure load of the constructs by 1.57±0.59 times (p = 0.026). Initial stiffness of the construct was also increased 3.13±2.10 times (p = 0.0079) with use of the bone peg. Conclusion: The stronger and stiffer construct provided by the addition of an intramedullary fibular allograft bone peg to locking plate fixation may help maintain reduction, and reduce the risk of fixation failure in surgical neck proximal humerus fractures with medial comminution.
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paper_title: Locking plate fixation of proximal humeral fractures with impaction of the fracture site to restore medial column support: a biomechanical study

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Background Despite the advent of locking plate techniques, proximal humeral fracture fixation can fail due to varus collapse, especially in osteoporotic bone with medial cortex comminution. This study investigated the effect of restoring the integrity of the medial column by fracture impaction and shaft medialization with locking plate fixation. This construct was compared with a traditional locking plate construct under conditions of varus cyclical loading. Materials and methods Proximal humeral fractures with medial comminution were simulated by performing wedge-shaped osteotomies at the surgical neck in cadaveric specimens and removing 1 cm of medial cortex. For each cadaver (n = 6), 1 humeral fracture was fixed with a traditional locking plate construct. The other was fixed with the locking plate construct plus fracture impaction and shaft medialization, resulting in medial column restoration. The humeral head was immobilized, and a repetitive, varus force was applied to the humeral shaft until construct collapse or until 25,000 cycles were completed. Results None of the constructs with fracture impaction collapsed, whereas 5 of 6 of the nonaugmented constructs collapsed before reaching 25,000 cycles ( P = .008). Collapse of the 5 nonimpacted constructs that failed occurred after an average of 11,470 ± 3589 cycles. Conclusion Fracture impaction increased the ability of the locking plate to withstand repetitive varus loading. This technique provides a construct biomechanically superior to locking plate fixation alone.
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paper_title: Locking Plate Fixation with and without Inferomedial Screws for Proximal Humeral Fractures: A Biomechanical Study

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PURPOSE. To compare the efficacy of locking plate fixation with and without inferomedial screws in maintaining the reduction of a proximal humeral fracture. METHODS. 22 synthetic humerus models were used. A standardised 3-part proximal humeral fracture with a 4-mm wedge segment was created and fixed with a locking plate and screws with (n=11) and without (n=11) inferomedial screws. The intrafragmentary motion of the construct at 250, 500, 750, and 1000 cycles of 532 N loading, and the load to failure of the 2 groups were compared. RESULTS. Locking plate fixation with inferomedial screws reduced the mean intrafragmentary motion in all cycles (p<0.01) and increased the load to failure (1452 N vs. 1159 N, p<0.001), compared to fixation without inferomedial screws. CONCLUSION. Additional inferomedial screws provide medial column support for fracture healing. This may reduce intrafragmentary motion and thus implant complications resulting from varus malalignment such as screw perforation or loss of reduction.
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paper_title: Proximal humerus fractures: a comparative biomechanical analysis of intra and extramedullary implants

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INTRODUCTION ::: The biomechanical stability of a newly developed humerus nail (Sirustrade mark) for the treatment of fractures of the proximal humerus was analyzed in comparison to established systems. In total, three randomized groups were formed (n = 4 pairs) from 12 matched pairs of human cadaver humeri. ::: ::: ::: MATERIALS AND METHODS ::: All intact bones were mechanically characterized by five subsequent load cycles under bending and torsional loading. The bending moment at the osteotomy was 7.5 N m the torsional moment was 8.3 N m over the hole specimen length. Loading was consistently initiated at the distal epiphysis and the deformation at the distal epiphysis was continuously recorded. Prior to implant reinforcement, a defect of 5 mm was created to simulate an unstable subcapital humerus fracture. For paired comparison, one humerus of each pair was stabilized with the Sirus proximal humerus nail while the counterpart was stabilized by a reference implant. In detail, the following groups were created: Sirus versus Proximal humerus nail (PHN) with spiral blade (group I); Sirus versus PHILOS plate (group II); Sirus versus 4.5 mm AO T-plate (group III). ::: ::: ::: RESULTS ::: The Sirus nail demonstrated significantly higher stiffness values compared to the reference implants for both bending and torsional loading. The following distal epiphyseal displacements were recorded for a bending moment of 7.5 N m at the osteotomy: Sirus I: 8.8 mm, II: 8.4 mm, III: 7.7 mm (range 6.9-10.9), PHN 21.1 mm (range 15.7-25.2) (P = 0.005), PHILOS plate 27.5 mm (range 21.6-35.8) (P < 0.001), 4.5 AO T-plate 26.3 mm (range 24.3-33.9) (P = 0.01). The rotations corresponding to 8.3 N m torsional moment were: Sirus I: 9.1 degrees , II: 9.3 degrees , III: 10.6 degrees (range 7.5-12.2), PHN 13.5 degrees (range 10.3-15.6) (P = 0.158), PHILOS plate 15.6 degrees (range 13.7-20.8) (P = 0.007), 4.5 AO T-Platte 14.1 degrees (range 11.5-19.7) (P = 0.158). ::: ::: ::: CONCLUSION ::: The intramedullary load carriers were biomechanically superior when compared to the plating systems in the fracture model presented here. Supplementary, the Sirus Nail showed higher stiffness values than the PHN. However, the latter are gaining in importance due to the possibility of minimal invasive implantation. Whether this will be associated with functional advantages requires further clinical investigation.
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paper_title: Locked plate fixation and intramedullary nailing for proximal humerus fractures: a biomechanical evaluation.

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Background: Internal fixation of proximal humeral fractures is associated with a considerable secondary malalignment rate. Fixed-angle implants have been suggested to increase the stability of fixation. Methods: The biomechanical properties of four different implants were tested. These included an internal fixator with semi-elastic properties (reference), the Synthes T-plate, a locked plate with rigid properties and a spiral blade locked intramedullary nail (PHN). These implants were assessed in twenty-four osteotomized pairs of human cadaveric humeri. Specimens were subjected to two-hundred cycles of axial loading and torque followed by load to failure. Results: The PHN had greater axial stiffness than the reference and the T-plate. During torque, all implants were stiffer than the reference. During cyclic loading, there were no differences between the T-plate and the reference. Both the rigid internal fixator and the PHN had less irreversible deformation than the reference. Both implants resisted higher loads before failure. Conclusion: This study showed that the proximal humeral nail and the rigid internal fixator are stronger than the semi-elastic locked plate and the Synthes T-plate for unstable subcapital proximal humeral fractures.
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paper_title: Relationship of cortical thickness of the proximal humerus and pullout strength of a locked plate and screw construct.

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BACKGROUND ::: No study to date has evaluated cortical thickness as it relates to locking plate failure or screw pullout in the proximal humerus. The purpose of this study is to determine the relationship between proximal humerus cortical thickness and locked plate hardware failure in a cadaveric proximal humerus fracture model. ::: ::: ::: METHODS ::: Twelve humerus specimens were placed into two groups based on the proximal humerus cortical thickness on an anteroposterior radiograph: less than 4 mm and greater than 4 mm. The specimens were plated with a six-hole proximal humerus locking plate and a 15-mm resection osteotomy at the surgical neck was performed. The specimens were tested in a materials testing machine at a displacement of 5 mm/min to failure. ::: ::: ::: RESULTS ::: Load at failure, stiffness, maximum load, failure, and fracture gap closure were all statistically similar (P > 0.05) between the groups. ::: ::: ::: CONCLUSION ::: Our biomechanical study used modern locked plate-screw construct fixation of a simulated two-part proximal humerus fracture. The mechanical strength was unaffected based on a threshold combined proximal humerus cortical thickness of 4 mm.
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paper_title: Biomechanical Contribution of Tension-Reducing Rotator Cuff Sutures in 3-Part Proximal Humerus Fractures.

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OBJECTIVES ::: Using a cadaveric 3-part fracture model and cyclic loading protocol, our study objectives were to quantify the stabilizing effect of tension-reducing rotator cuff sutures in terms of fracture displacement across the surgical neck and greater tuberosity compared with a control group in which no sutures were used. ::: ::: ::: METHODS ::: Six matched pairs of fresh frozen specimens underwent a standardized, 3-part, proximal humerus fracture and were split into 2 groups. The control group had the fracture fixed with a plate and screw construct only while the experimental group had additional suture fixation through the plate to each rotator cuff tendon. Active abduction through the rotator cuff was simulated for 100, 200, 300, and 400 cycles and to failure at 1000 N. A Mann-Whitney U test compared cyclic displacement of the greater tuberosity and surgical neck fracture gaps and load to failure between the 2 groups. ::: ::: ::: RESULTS ::: There was no significant difference (P > 0.05) in fracture gap between fixation methods at the surgical neck at 100 (P = 0.13), 200 (P = 0.07), 300 (P = 0.49), and 400 (P = 0.07) cycles. There was no significant difference (P > 0.05) between fixation methods in the fracture gap at the greater tuberosity at 100 (P = 0.39), 200 (P = 1.00), 300 (P = 0.31), and 400 (P = 0.59) cycles. There was no significant difference (P > 0.5) at 1000 N at the surgical neck (P = 0.70) or the greater tuberosity (P = 0.39). ::: ::: ::: CONCLUSIONS ::: Tension-relieving rotator cuff sutures do not add stability to the repair of 3-part proximal humerus fractures. Varus collapse and greater tuberosity displacement are common complications associated with 3-part fractures. No mechanical data exist to demonstrate benefit of adding suture to a plate and screw construct for limiting fracture displacement.
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paper_title: Mechanical Assessment of Local Bone Quality to Predict Failure of Locked Plating in a Proximal Humerus Fracture Model

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The importance of osteoporosis in proximal humerus fractures is well recognized. However, the local distribution of bone quality in the humeral head may also have a significant effect because it remains unclear in what quality of bone screws of standard implants purchase. The goal of this study was to investigate whether the failure of proximal humerus locked plating can be predicted by the DensiProbe (ARI, Davos, Switzerland). A 2-part fracture with metaphyseal impaction was simulated in 12 fresh-frozen human cadaveric humeri. Using the DensiProbe, local bone quality was determined in the humeral head in the course of 6 proximal screws of a standard locking plate (Philos; Synthes GmbH, Solothurn, Switzerland). Cyclic mechanical testing with increasing axial loading until failure was performed. Bone mineral density (BMD) significantly correlated with cycles until failure. Head migration significantly increased between 1000 and 2000 loading cycles and significantly correlated with BMD after 3000 cycles. DensiProbe peak torque in all screw positions and their respective mean torque correlated significantly with the BMD values. In 3 positions, the peak torque significantly correlated with cycles to failure; here BMD significantly influenced mechanical stability. The validity of the DensiProbe was proven by the correlation between its peak torque measurements and BMD. The correlation between the peak torque and cycles to failure revealed the potential of the DensiProbe to predict the failure of locked plating in vitro. This method provides information about local bone quality, potentially making it suitable for intraoperative use by allowing the surgeon to take measures to improve stability.
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paper_title: The biomechanical performance of locking plate fixation with intramedullary fibular strut graft augmentation in the treatment of unstable fractures of the proximal humerus

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We evaluated the biomechanical properties of two different methods of fixation for unstable fractures of the proximal humerus. Biomechanical testing of the two groups, locking plate alone (LP), and locking plate with a fibular strut graft (LPSG), was performed using seven pairs of human cadaveric humeri. Cyclical loads between 10 N and 80 N at 5 Hz were applied for 1,000,000 cycles. Immediately after cycling, an increasing axial load was applied at a rate of displacement of 5 mm/min. The displacement of the construct, maximum failure load, stiffness and mode of failure were compared. The displacement was significantly less in the LPSG group than in the LP group (p = 0.031). All maximum failure loads and measures of stiffness in the LPSG group were significantly higher than those in the LP group (p = 0.024 and p = 0.035, respectively). In the LP group, varus collapse and plate bending were seen. In the LPSG group, the humeral head cut out and the fibular strut grafts fractured. No broken plates or screws were seen in either group. We conclude that strut graft augmentation significantly increases both the maximum failure load and the initial stiffness of this construct compared with a locking plate alone.
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paper_title: Retrograde nailing versus locking plate osteosynthesis of proximal humeral fractures: a biomechanical study

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Background In locking plate osteosynthesis of proximal humeral fractures, secondary varus malalignment is a specific complication. Retron nails (Tantum AG, Neumunster, Germany), among others, have been designed to improve medial support of the calcar humeri. The aim of our biomechanical study was to examine whether Retron nails provide increased stiffness for axial loads and adequate stiffness for torsional loads when compared with Philos plates (Synthes AG, Umkirch, Germany). Materials and methods Twenty-two fresh-frozen paired humeri were collected. After potting the specimens, intact bones were exposed to sinusoidal axial (10-120 N) and torsional (±2.5 Nm) loading for 8 cycles to calculate the initial stiffness and exclude pairs with differences. Afterward, an unstable proximal humeral fracture (AO 11-A3) was created by means of an oscillating saw, and the respective osteosynthesis devices were implanted. After another 4 cycles, initial changes in stiffness were measured. Subsequently, all specimens were tested for 1,000 cycles of loading before final stiffness was assessed. Results We found no statistically significant differences between Retron and Philos specimens after 4 or 1,000 cycles of loading. Conclusion Our study suggests that retrograde nailing provides sufficient stability for axial and torsional loading in 2-part fractures of proximal humeri.
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paper_title: Mechanical evaluation of a new minimally invasive device for stabilization of proximal humeral fractures in elderly patients: a cadaver study.

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BACKGROUND ::: Treatment of proximal humerus fractures in elderly patients is challenging because of reduced bone quality. We determined the in vitro characteristics of a new implant developed to target the remaining bone stock, and compared it with an implant in clinical use. ::: ::: ::: METHODS ::: Following osteotomy, left and right humeral pairs from cadavers were treated with either the Button-Fix or the Humerusblock fixation system. Implant stiffness was determined for three clinically relevant cases of load: axial compression, torsion, and varus bending. In addition, a cyclic varus-bending test was performed. ::: ::: ::: RESULTS ::: We found higher stiffness values for the humeri treated with the ButtonFix system--with almost a doubling of the compression, torsion, and bending stiffness values. Under dynamic loading, the ButtonFix system had superior stiffness and less K-wire migration compared to the Humerusblock system. ::: ::: ::: INTERPRETATION ::: When compared to the Humerusblock design, the ButtonFix system showed superior biomechanical properties, both static and dynamic. It offers a minimally invasive alternative for the treatment of proximal humerus fractures.
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paper_title: Proximal humerus fracture rotational stability after fixation using a locking plate or a fixed-angle locked nail: The role of implant stiffness

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Abstract Background Fixed-angle locked devices have been developed to improve internal fixation of proximal humerus fractures. Available low-profile precontoured locking plates and intramedullary nails with fixed-angle interlocks are currently favored by most surgeons in this setting. The aim of this study was to assess the relative stability of these two methods of fixation under torsion load. Methods A surgical neck osteotomy was created in six pairs of embalmed humeri. In each pair, one specimen was secured with a titanium locking-compression plate, and the contralateral was secured with a titanium nail with a proximal locked spiral blade. The specimens were first tested cyclically in internal–external rotation for 10,000 cycles to evaluate interfragmentary motion (dynamic study). At the end of the cyclic testing, the specimens were loaded to failure in external rotation to measure torque to failure and construct stiffness (static study). Findings There were no significant differences in interfragmentary motion between the two fixation devices in the dynamic study. When tested to failure, fixation with the locking plate tolerated on average 20 more degrees in torsion before failure, and demonstrated higher torsional load to failure and less torsional stiffness ( P Interpretation Both locking plates and locked intramedullary nails may provide enough stability to avoid secondary displacement of proximal humerus fractures during early physical therapy. Locking plates demonstrated superior biomechanical properties under high rotational loads than locked intramedullary nails in a cadaveric proximal humerus two-part osteotomy model, and could provide more protection against unexpected high torsion loads.
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paper_title: Semitubular blade plate fixation in proximal humeral fractures: A biomechanical study in a cadaveric model

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This study was undertaken to compare the fixation of the semitubular blade plate with that of the AO T plate. Cadaveric humeri (n = 12 pairs) from an elderly population (41 to 89 years) had either a blade plate (n = 12) or a T plate (n = 12) fixed to them, subsequent to which a transverse osteotomy was performed. Mechanical testing in tension was performed in 1 series (n = 5, blade plate; n = 5, T plate) by applying a single maximal load to failure and in a second series (n = 7, blade plate; n = 7, T plate) by applying submaximal cyclic loading before failure was induced. Results showed that the fixation provided by the semitubular blade plate was significantly better (P <.05) than that of the T plate in those specimens subjected to submaximal cyclic loading before failure (series 2). This latter testing method contains some component of the clinical situation compared with monotonic distraction to failure. Based on these results plus favorable clinical results reported in the literature, the semitubular blade plate is possibly a better alternative to the T plate in the management of proximal humeral fractures that require open reduction and internal fixation. (J Shoulder Elbow Surg 1998;7:462-6.)
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paper_title: Mechanisms of failure of locked-plate fixation of the proximal humerus: acoustic emissions as a novel assessment modality.

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OBJECTIVES ::: Locking plates are the predominant implants used for proximal humerus fractures. Despite a preponderance of good clinical outcomes, failures continue to occur. The purpose of this study was to investigate the failure mechanism of locked proximal humeral plate fixation and its relationship with bone density and screw length. ::: ::: ::: METHODS ::: Human cadaveric humeri were subjected to cyclic bending loads after an unstable 2-part fracture (Orthopedic Trauma Association classification 11 A-3) was created and stabilized with a locking proximal humeral plate. Acoustic emission (AE) sensors were mounted on the specimens to detect fracture displacement and generation of microcracks. The data were analyzed to evaluate construct failure. ::: ::: ::: RESULTS ::: Eight of 10 locking plate constructs in cadaver specimens failed in varus collapse. The primary influences on failure were cancellous bone density and cancellous bone screw length. AE monitoring demonstrated patterns of microcrack progression, predominantly along the inferior screws. The progression trends according to AE were similar to their respective actuator displacement versus time curves. ::: ::: ::: CONCLUSIONS ::: Cancellous bone density and total cancellous screw depth penetration seem to be critical variables. Although the patients' bone density cannot be controlled, surgeons may decrease the risk of failure by maximizing the length of the screws within the cancellous bone. Analysis of microcrack formation revealed that failures begin at the midportion and tips of the inferior screws and at the bone-plate interface of the inferior screws.
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paper_title: Locked vs. unlocked plate osteosynthesis of the proximal humerus - a biomechanical study.

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BACKGROUND ::: Locked plates (internal fixators) have been found to be an optimal method for the fixation in proximal humeral fractures. In a biomechanical cadaver study the difference between locked and non-locked osteosyntheses was investigated. ::: ::: ::: METHODS ::: Paired humeri were harvested, bone density measured. Locked internal fixators were mounted on one specimen; identical plate-screw-systems without locking mechanism applied to the contralateral specimen for comparison. After that, a transverse subcapital osteotomy was performed. With 7 pairs of humeri static tests with increasing axial loads and with 5 pairs dynamic tests with 10 N preload and 80 N maximal axial load for up to 1 million cycles were performed. ::: ::: ::: RESULTS ::: In the static experiments the elastic stiffness of the construct was 74% higher in the locked group (median 80 N/mm, quartile range 77-86 N/mm) compared with the non-locked group (46 N/mm, 35.5-56.5 N/mm). The difference was statistically significant (Wilcoxon test for paired samples, P<0.05). Similarly, the linear range until failure was definitely extended in the locked group by 64% (92 N, 89-98 N vs. 56 N, 36.5-73.5 N, P<0.05). Under dynamic loading the non-locked group showed fixation failures between 97,000 and 500,000 cycles. In the locked group no failure was observed until the end of the experiment at 1 million cycles (P<0.0.5). The final deformation was found to be 1 mm (median, quartil range 1.0-1.2 mm) in the non-locked group and 0.3 mm (0.2-0.3 mm) in the locked group (P<0.05). The differences were found equally in lower as well as in higher bone density specimen. ::: ::: ::: INTERPRETATION ::: Because of the optimal load transfer between implant and cancellous bone, a locked screw plate interface will reduce fixation failure in proximal humeral fractures.
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paper_title: Screw augmentation reduces motion at the bone-implant interface: a biomechanical study of locking plate fixation of proximal humeral fractures.

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BACKGROUND ::: Shear forces at the bone-implant interface lead to a loss of reduction after locking plate fixation of proximal humeral fractures. The aim of the study was to analyze the roles of medial support screws and screw augmentation in failure loads and motion at the bone-implant interface after locking plate fixation of proximal humeral fractures. ::: ::: ::: METHODS ::: Unstable 3-part fractures were simulated in 6 pairs of cadaveric humeri and were fixed with a DiPhos-H locking plate (Lima Corporate, Udine, Italy). An additional medial support screw was implanted in 1 humerus of every donor. The opposite humerus was stabilized with a medial support screw and additional bone cement augmentation of the 2 anteriorly directed head screws. Specimens were loaded in the varus bending position. Stiffness, failure loads, plate bending, and the motion at the bone-implant interface were evaluated using an optical motion capture system. ::: ::: ::: RESULTS ::: The mean load to failure was 669 N (standard deviation [SD], 117 N) after fixation with medial support screws alone and 706 N (SD, 153 N) after additional head screw augmentation (P = .646). The initial stiffness was 453 N/mm (SD, 4.16 N/mm) and 461 N/mm (SD, 64.3 N/mm), respectively (P = .594). Plate bending did not differ between the 2 groups. However, motion at the bone-implant interface was significantly reduced after head screw augmentation (P < .05). ::: ::: ::: CONCLUSION ::: The addition of bone cement to augment anteriorly directed head screws does not increase stiffness and failure loads but reduces motion at the bone-implant interface. Thus, the risk of secondary dislocation of the head fragment may be reduced.
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paper_title: Proximal humeral fracture fixation: a biomechanical comparison of two constructs.

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BACKGROUND ::: Different options exist for stabilizing proximal humeral fractures. This study compared the mechanical stability of 2 common proximal humeral fixation plates in bending and torsion. ::: ::: ::: METHODS ::: Tests were conducted on 40 synthetic and 10 matched pairs of cadaveric humeri (evenly fixed with DePuy S3 proximal humeral plating system [DePuy Orthopaedics, Warsaw, IN, USA] and Synthes proximal humerus locking compression plate [Synthes, Paoli, PA, USA]). Half of the humeri were tested by cantilevered bending in flexion, extension, varus, and valgus for 100 cycles of ±5 mm of displacement at 1 mm/s before loading to failure in varus. The other half were tested in torsion for 100 cycles of ±8° of rotational displacement at 1°/s before loading to failure in external rotation. ::: ::: ::: RESULTS ::: Peak cyclic loads for synthetic constructs were higher for DePuy plates than Synthes plates in varus and valgus (P < .0001), but a difference was not detected in extension (P > .40) or flexion (P = .0675). Peak cyclic loads for cadaveric constructs showed a significant difference in extension and flexion (Synthes > DePuy, P < .0001) and in varus (DePuy > Synthes, P < .05) but not in valgus (P > .10). Bending stiffness during varus failure testing was higher for DePuy plates than Synthes plates (P < .0001) for synthetic constructs. Regarding torsion of synthetic and cadaveric constructs, DePuy plates experienced higher peak cyclic torques over all cycles in both directions (P < .0001). For synthetic constructs, DePuy plates showed higher torsional stiffness in external failure than Synthes plates (P < .0001). ::: ::: ::: CONCLUSIONS ::: The DePuy plate was stiffer than the Synthes plate with varus and valgus bending, as well as in torsion. The Synthes plate tended to be stiffer in flexion and extension.
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paper_title: Forces at the Glenohumeral Joint in Abduction

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The purpose of this study was to determine the forces in the glenohumeral joint for isometric abduction (including all directions of rotation) in the plane of the scapula. The lines of actions of muscles were obtained from 3 upper quarter specimens, electromyographic data was used, as well as geometrical parameters of shoulder motion. The main assumption made in the analysis was that the force in a muscle was proportional to its area times the integrated electromyographic signal. The resultant force reached a maximum of 0.89 times body weight at 90 degrees of abduction, while the shearing component up the face of the glenoid was a maximum of 0.42 times body weight at 60 degrees of abduction.
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paper_title: Intramedullary cortical bone strut improves the cyclic stability of osteoporotic proximal humeral fractures

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Proximal humeral fractures treated with locking plate can fail due to varus collapse, especially in osteoporotic bone with medial cortex comminution. The use of an intramedullary strut together with locking plate fixation may strengthen fixation and provide additional medial support to prevent the varus malalignment. This study biomechanically investigates the influence of an intramedullary cortical bone strut on the cyclic stability of proximal humeral fractures stabilized by locking plate fixation in a cadaver model. Ten cadaveric humeri were divided into two groups statistically matched for bone density. Each specimen was osteotomized with 10 mm gap at the surgical neck. The non-augmented group stabilized with locking plate alone; in the augmented group, a locking plate was used combined with an intramedullary cortical bone strut. The strut was retrograded into the subchondral bone, and three humeral head screws were inserted into the strut to form a plate-screw-strut mechanism. The cyclic axial load was performed to 450 N for 6000 cycles and then loaded to failure. Construct stiffness, cyclic loading behavior and failure strength were analyzed to identify differences between groups. The augmented constructs were significantly stiffer than the non-augmented constructs during cycling. On average, the maximum displacements at 6000 cycles for non-augmented and augmented groups were 3.10 ± 0.75 mm and 1.7 ± 0.65 mm (p = 0.01), respectively. The mean peak-to-peak (inter cycle) displacement at 6000 cycles was about 2 times lower for the augmented group (1.36 ± 0.68 mm vs. 2.86 ± 0.51 mm). All specimens showed varus collapse combined with loss of screw fixation of the humeral head. The failure load of the augmented group was increased by 2.0 (SD = 0.41) times compared with the non-augmented group (p < 0.001). The stability and strength of the locking plate augmented with an intramedullary strut were significantly increased. For bone with poor quality, the subsidence of the locked screws led larger displacement, decreased the stability of the constructs, however, the plate-screw-strut mechanism provided more rigidity to stabilize the fixation. This study emphasized the importance of intramedullary support for the proximal humeral fractures fixed with a locked plate under cyclic loading, especially in bone with poor quality. This work is based on the results of cadaver model, further in vivo analysis is necessary to determine if the clinical results can be extrapolated from this data.
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paper_title: Biomechanical in vitro assessment of screw augmentation in locked plating of proximal humerus fractures

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Abstract Introduction Proximal humerus fracture fixation can be difficult because of osteoporosis making it difficult to achieve stable implant anchorage in the weak bone stock even when using locking plates. This may cause implant failure requiring revision surgery. Cement augmentation has, in principle, been shown to improve stability. The aim of this study was to investigate whether augmentation of particular screws of a locking plate aimed at a region of low bone quality is effective in improving stability in a proximal humerus fracture model. Materials and methods Twelve paired human humerus specimens were included. Quantitative computed tomography was performed to determine bone mineral density (BMD). Local bone quality in the direction of the six proximal screws of a standard locking plate (PHILOS, Synthes) was assessed using mechanical means (DensiProbe™). A three-part fracture model with a metaphyseal defect was simulated and fixed with the plate. Within each pair of humeri the two screws aimed at the region of the lowest bone quality according to the DensiProbe™ were augmented in a randomised manner. For augmentation, 0.5 ml of bone cement was injected in a screw with multiple outlets at its tip under fluoroscopic control. A cyclic varus-bending test with increasing upper load magnitude was performed until failure of the screw–bone fixation. Results The augmented group withstood significantly more load cycles. The correlation of BMD with load cycles until failure and BMD with paired difference in load cycles to failure showed that augmentation could compensate for a low BMD. Discussion and conclusion The results demonstrate that augmentation of screws in locked plating in a proximal humerus fracture model is effective in improving primary stability in a cyclic varus-bending test. The augmentation of two particular screws aimed at a region of low bone quality within the humeral head was almost as effective as four screws with twice the amount of bone cement. Screw augmentation combined with a knowledge of the local bone quality could be more effective in enhancing the primary stability of a proximal humerus locking plate because the effect of augmentation can be exploited more effectively limiting it to the degree required.
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paper_title: Biomechanical comparison of a proximal humeral locking plate using two methods of head fixation.

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HYPOTHESIS ::: Locking plates have emerged as the implant of choice for stabilization of proximal humeral fractures. The biomechanical properties of a locked plating system using smooth pegs vs threaded screws for fixation of the humeral head were compared to test the hypothesis that there would be no biomechanical difference between pegs and threaded screws. ::: ::: ::: MATERIALS AND METHODS ::: Sixteen pairs of fresh frozen cadaveric humeri were randomized to have a surgical neck gap osteotomy stabilized with a locked plate using threaded screws (n=8) or smooth pegs (n=8). The intact contralateral humerus served as a control. Each specimen was tested with simultaneous cyclic axial compression (40 Nm) and torsion (both +/-2 Nm and +/-5 Nm) for 6000 cycles. All specimens were loaded to failure. Interfragmentary motion and load-displacement curves were analyzed to identify differences between the groups. Our data were then compared to previously published forces across the glenohumeral joint to provide evidence based recommendations for postoperative use of the shoulder. ::: ::: ::: RESULTS ::: There was a statistically significant difference between test specimens and their paired control (P < .001) in cyclic testing and load to failure. Differences between the smooth pegs and threaded screws were not statistically significant. ::: ::: ::: DISCUSSION ::: There is no biomechanical difference between locked smooth pegs and locked threaded screws for proximal fragment fixation in an unstable 2-part proximal humeral fracture model. ::: ::: ::: CONCLUSION ::: Our study contributes to the published evidence evaluating forces across the glenohumeral joint and suggests that early use of the affected extremity for simple activities of daily living may be safe. Use of the arm for assisted ambulation requiring a crutch, cane, walker, or wheelchair should be determined on a case-by-case basis.
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paper_title: Influence of plate material and screw design on stiffness and ultimate load of locked plating in osteoporotic proximal humeral fractures

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Abstract Introduction The main purpose was to compare the biomechanical properties of a carbon-fibre reinforced polyetheretherketone (CF-PEEK) composite locking plate with pre-existing data of a titanium-alloy plate when used for fixation of an unstable 2-part fracture of the surgical neck of the humerus. The secondary purpose was to compare the mechanical behaviour of locking bolts and conventional locking cancellous screws. Methods 7 pairs of fresh frozen human humeri were allocated to two equal groups. All specimens were fixed with the CF-PEEK plate. Cancellous screws (PEEK/screw) were compared to locking bolts (PEEK/bolt) for humeral head fixation. Stiffness, fracture gap deflection and ultimate load as well as load before screw perforation of the articular surface were assessed. Results were compared between groups and with pre-existing biomechanical data of a titanium-alloy plate. Results The CF-PEEK plate featured significantly lower stiffness compared to the titanium-alloy plate ( P P > 0.05). Discussion The CF-PEEK plate has more elastic properties and significantly increases movement at the fracture site of an unstable proximal humeral fracture model compared to the commonly used titanium-alloy plate. The screw design however does neither affect the constructs primary mechanical behaviour in the constellation tested nor the load before screw perforation.
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paper_title: Biomechanical comparison of an angular stable plate with augmented and non-augmented screws in a newly developed shoulder test bench.

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BACKGROUND ::: The proximal humeral fracture is one of the most common fractures. Although there are a number of treatment options available, the clinical outcomes in geriatric patients are still unsatisfactory. Therefore, the aim of this study was to investigate the biomechanical behaviour of an angular stable plate with either augmented or non-augmented screws using two different fracture models in a shoulder test bench with active muscle forces. ::: ::: ::: METHODS ::: Six paired fresh-frozen humeri were loaded into a shoulder test bench simulating ab- and adduction between 15 and 45° induced by active muscle forces. The bone mineral density was measured by a quantitative CT. A two-part fracture model (stable and an unstable) was used to investigate the different biomechanical behaviours of the PHILOS plate, either utilising cannulated screws, allowing in situ augmentation, or without utilising augmented screws. Four screws were augmented with 0.5ml PMMA cement. ::: ::: ::: FINDINGS ::: The in vitro-measured resulting forces in the glenoid fossa were comparable to the in vivo forces generated in shoulder arthroplasties. Under stable conditions, the per cycle motion and varus impaction tilting showed no significant difference. In the unstable state, the augmented group showed a maximum of 0.81° per cycle motion and a maximum varus impaction of -1.46° compared to the non-augmented maximum of 2.31° per cycle motion and maximum varus impaction of -4.26° (P<0.05). ::: ::: ::: INTERPRETATION ::: In an unstable fracture model under dynamic testing conditions, augmentation leads to a decreased per cycle motion and varus impaction of the humeral head.
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paper_title: BIOMECHANICAL EVALUATION OF PROXIMAL HUMERAL FRACTURE FIXATION SUPPLEMENTED WITH CALCIUM PHOSPHATE CEMENT

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Background: Proximal humeral fractures are common injuries, and numerous surgical methods have been described for their treatment. The biomechanical characteristics of various internal fixation devices that are used to treat these fractures have not been extensively studied, nor has the potential beneficial effect of calcium phosphate cement supplementation. Methods: We used a cadaveric three-part proximal humeral osteotomy model to perform a biomechanical evaluation of three types of internal fixation devices: a cloverleaf plate, an angled blade-plate, and Kirschner wires. The effect of supplementing the fixation with SRS (Skeletal Repair System) calcium phosphate cement was evaluated as well. Eighteen pairs of fresh-frozen humeri were obtained, and the bone-mineral density of each specimen was measured. In each pair, one specimen was secured with internal fixation alone and the contralateral specimen was secured with internal fixation combined with calcium phosphate cement. The specimens were tested cyclically in abduction and in external rotation for 250 cycles to evaluate interfragmentary motion. The specimens were then loaded to failure in external rotation to measure torsional load to failure and torsional stiffness. Results: Overall, there were no significant differences between the specimens treated with the blade and cloverleaf plates, whereas the specimens treated with Kirschner wires demonstrated more interfragmentary motion, less stiffness, and lower torque to failure. In general, supplementation with calcium phosphate cement led to significant improvements in the mechanical performance of all three forms of internal fixation as demonstrated by a significant decrease in interfragmentary motion, a significant increase in torque to failure, and a significant increase in torsional stiffness. The addition of calcium phosphate cement increased the stiffness of even the most osteoporotic specimens to levels that were higher than those of the most osteodense specimens that had been treated with internal fixation alone. Conclusion: The initial biomechanical properties of internal fixation as measured with use of a proximal humeral osteotomy model and three methods of fixation were significantly improved by the addition of calcium phosphate cement. Clinical Relevance: The addition of calcium phosphate cement may augment the mechanical characteristics of internal fixation of difficult, three-part proximal humeral fractures. The ability to stabilize the interface between the implant and cancellous bone, particularly in the presence of osteopenia, may make calcium phosphate cement a valuable clinical tool in the treatment of these difficult fractures.
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paper_title: Proximal humeral fracture fixation: locking plate construct ± intramedullary fibular allograft.

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BACKGROUND ::: Locking plate constructs for proximal humeral fractures can fail due to varus collapse, especially in osteoporotic bone with medial cortex comminution. Augmentation, using a fibular allograft as an intramedullary bone peg, may strengthen fixation preventing varus collapse. This study investigated the ability of the augmented locking plate construct to withstand repetitive varus stresses relative to the nonaugmented construct. ::: ::: ::: MATERIALS AND METHODS ::: Proximal humeral fractures with medial comminution were simulated by performing wedge-shaped osteotomies at the surgical neck in cadaveric specimens. For each cadaver (n = 8), 1 humeral fracture was fixated with the locking plate construct alone and the other with the locking plate construct plus ipsilateral fibular autograft augmentation. The humeral head was immobilized and a repetitive, medially directed load was applied to the humeral shaft until construct collapse or until 25000 cycles were completed. ::: ::: ::: RESULTS ::: No augmented construct collapsed. In comparison, 6 of 8 nonaugmented constructs collapsed (P < .05). Collapse in the 6 nonaugmented constructs occurred after an average ±SD of 6604 ± 1984 cycles. Screw penetration of the articular surface was found in only 1 of the nonaugmented constructs. ::: ::: ::: CONCLUSION ::: Fibular allograft augmentation increased the ability of the locking plate to withstand repetitive varus loading. Clinically, this may assist proximal humeral fracture fixation in osteoporotic bone with medial cortex comminution.
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paper_title: PEEK versus titanium locking plates for proximal humerus fracture fixation: a comparative biomechanical study in two- and three-part fractures

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Introduction ::: The high rigidity of metal implants may be a cause of failure after fixation of proximal humerus fractures. Carbon fiber-reinforced polyetheretherketone (PEEK) plates with a modulus similar to human cortical bone may help to overcome this problem. The present study assesses the biomechanical behavior of a PEEK plate compared with a titanium locking plate.
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paper_title: Monoaxial versus polyaxial locking systems: a biomechanical analysis of different locking systems for the fixation of proximal humeral fractures

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Objective ::: The development of locking plate systems has led to polyaxial screws and new plate designs. This study compares monoaxial head locking screws (PHILOS© by Synthes) and a new generation of polyaxial locking screws (NCB-LE© by Zimmer) with respect to biomechanical stability.
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paper_title: The Humerusblock NG: a new concept for stabilization of proximal humeral fractures and its biomechanical evaluation

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Background ::: The Humerusblock NG represents a new semi-rigid angular stable fixation device for minimally invasive stabilization of proximal humeral fractures. This study evaluates the function and stability of the Humerusblock NG and its biomechanical properties on the basis of two different fracture models under cyclic loading.
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paper_title: The Evolution of Locked Plates

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Our purpose is to review the history of locked plates and the current recommendations for the use of those devices and to look toward future trends in the clinical application of locked plates. We will discuss (1) the impetus for the locked (fixed-angle) plate design, (2) current indications and design trends, (3) the latest clinical and biomechanical data, (4) shortcomings of locked (fixed-angle) plates, and (5) future applications and directions for locked (fixed-angle) plates. ::: ::: Since their initial introduction in the late nineteenth century and their subsequent popularization by Danis1-3 and the Arbeitsgemeinschaft fur Osteosynthesefragen (AO) group in the 1960s, conventional nonlocked plates have proven, over time, to successfully stabilize many types of fractures and osteotomy sites. The plate-screw-bone construct must resist physiological loads to allow fracture union by limiting fracture gap stress, provide sufficient stability to permit early limb motion, and not fail before fracture union occurs. Additionally, for optimal clinical results, disruption of the bone blood supply by the plate-screw-bone construct should be minimized. To accomplish this goal, there should be minimal operative dissection and periosteal contact to promote bone union4,5. Ideally, the plate-screw-bone construct will permit the restoration of the mechanical limb alignment and reestablish joint congruity to within <2 mm2,6,7. Finally, to be successful, plate fixation must provide reproducible results, must be simple to perform, and must have broad clinical applicability. ::: ::: Fixation with conventional compression plates, although for the most part successful, has its limitations. Figure 1 demonstrates one attempt to counter the limitations associated with the use of conventional nonlocked plates. To achieve fracture stability, the axial, torsional, and three-point bending forces must be neutralized (Fig. 2). With the use of conventional nonlocked plates, force friction between the plate and the bone counters …
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paper_title: Locking plates improve torsional resistance in the stabilization of three-part proximal humeral fractures.

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This study quantified the torsional resistance provided by locking plates and angled blade plates used to stabilize proximal humeral fractures. Three-part proximal humeral fractures were created in 6 pairs of cadaveric humeri. One specimen of each pair was reconstructed with a proximal humeral locking plate, whereas the other specimen was reconstructed with an angled blade plate. An external rotation torque, varying from 0 to 5 N-m, was applied to the humeral head until the head rotated 30 degrees or 10,000 loading cycles were applied. The mean initial torsional stiffness was significantly larger for the locking plates (0.99 N-m/degree) than for the blade plates (0.59 N-m/degree). For each pair, the maximum rotation was larger for the blade plate than for the locking plate. For this in vitro model of a reconstructed 3-part proximal humeral fracture, the locking plate provided better torsional fatigue resistance and stiffness than the blade plate.
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paper_title: Biomechanical comparison of a unique locking plate versus a standard plate for internal fixation of proximal humerus fractures in a cadaveric model.

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BACKGROUND ::: Newer internal fixation devices with a locking mechanism between the plate and the screw have recently been released. The efficacy of these plates in the proximal humerus has yet to be fully described. There is a need to compare the biomechanical properties of efficacy of plate fixation with or without locking screws for surgery of two-part proximal humerus fractures. Multiple-plane locking plate and cloverleaf plate designs were tested to determine their ability to maintain fixation on the humeral head. ::: ::: ::: METHODS ::: Eight matched pairs of cadaveric shoulders with 7-millimeter osteotomy defects at the surgical neck simulating two-part fractures of the proximal humerus were loaded to failure in thirty degrees of glenohumeral abduction. One side was repaired with a proximal humerus locking plate and the other with a cloverleaf plate. The rotator cuff musculature was then loaded via a servo-hydraulic testing machine under displacement control to simulate the deforming forces present in vivo. ::: ::: ::: FINDINGS ::: The average maximum load to failure was greater in proximal humerus locking plates than in cloverleaf plates (876 versus 712; P=0.04). ::: ::: ::: INTERPRETATION ::: In the cadaveric, two-part proximal humerus fracture model that was created, the locking plate displayed significantly greater holding power of the humeral head. Clinical relevance is unproven but may be manifested in vivo as improved early range of motion exercises and functional outcome.
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paper_title: Biomechanical Analysis of Blade Plate Versus Locking Plate Fixation for a Proximal Humerus Fracture: Comparison Using Cadaveric and Synthetic Humeri

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Objective:To compare the mechanical stability of a fixed-angle blade plate with that of a locking plate in a cadaveric proximal humerus fracture-fixation model subjected to cyclic loading. A secondary objective was to evaluate whether the use of synthetic humerus specimens would replicate significan
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paper_title: Biomechanics of Locked Plates and Screws

paper_content:

Objective:To review the biomechanical principles that guide fracture fixation with plates and screws; specifically to compare and contrast the function and roles of conventional unlocked plates to locked plates in fracture fixation. We review basic plate and screw function, discuss the design ration
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paper_title: BIOMECHANICAL EVALUATION OF PROXIMAL HUMERAL FRACTURE FIXATION SUPPLEMENTED WITH CALCIUM PHOSPHATE CEMENT

paper_content:

Background: Proximal humeral fractures are common injuries, and numerous surgical methods have been described for their treatment. The biomechanical characteristics of various internal fixation devices that are used to treat these fractures have not been extensively studied, nor has the potential beneficial effect of calcium phosphate cement supplementation. Methods: We used a cadaveric three-part proximal humeral osteotomy model to perform a biomechanical evaluation of three types of internal fixation devices: a cloverleaf plate, an angled blade-plate, and Kirschner wires. The effect of supplementing the fixation with SRS (Skeletal Repair System) calcium phosphate cement was evaluated as well. Eighteen pairs of fresh-frozen humeri were obtained, and the bone-mineral density of each specimen was measured. In each pair, one specimen was secured with internal fixation alone and the contralateral specimen was secured with internal fixation combined with calcium phosphate cement. The specimens were tested cyclically in abduction and in external rotation for 250 cycles to evaluate interfragmentary motion. The specimens were then loaded to failure in external rotation to measure torsional load to failure and torsional stiffness. Results: Overall, there were no significant differences between the specimens treated with the blade and cloverleaf plates, whereas the specimens treated with Kirschner wires demonstrated more interfragmentary motion, less stiffness, and lower torque to failure. In general, supplementation with calcium phosphate cement led to significant improvements in the mechanical performance of all three forms of internal fixation as demonstrated by a significant decrease in interfragmentary motion, a significant increase in torque to failure, and a significant increase in torsional stiffness. The addition of calcium phosphate cement increased the stiffness of even the most osteoporotic specimens to levels that were higher than those of the most osteodense specimens that had been treated with internal fixation alone. Conclusion: The initial biomechanical properties of internal fixation as measured with use of a proximal humeral osteotomy model and three methods of fixation were significantly improved by the addition of calcium phosphate cement. Clinical Relevance: The addition of calcium phosphate cement may augment the mechanical characteristics of internal fixation of difficult, three-part proximal humeral fractures. The ability to stabilize the interface between the implant and cancellous bone, particularly in the presence of osteopenia, may make calcium phosphate cement a valuable clinical tool in the treatment of these difficult fractures.
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paper_title: Biomechanical in vitro assessment of fixed angle plating using a new concept of locking for the treatment of osteoporotic proximal humerus fractures

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Locked plating attempts to improve mechanical stability via better anchorage of the screws in the bone. In 22 paired osteoporotic humeri an AO/ASIF 11-B 1 fracture was created. Locked and conventional plating using the same device of the latest generation was performed. Torsional loading around three axes (x = varus/valgus, y = flexion/extension, z = axial rotation) with an increasing moment (2, 3.5, 5 and 7.5 N·m) was applied. Interfragmentary motion within the locked group was lower for all three axes with higher cumulative survival rates (p < 0.05). The typical mode of failure was loss of fixation in the humeral head occurring earlier in the conventional group. The locking mechanism investigated provides more ultimate strength in an osteoporotic proximal humerus fracture model. Correlation with BMD suggests that this device may especially be suitable for use in osteoporotic bone.
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paper_title: Monoaxial versus polyaxial locking systems: a biomechanical analysis of different locking systems for the fixation of proximal humeral fractures

paper_content:

Objective ::: The development of locking plate systems has led to polyaxial screws and new plate designs. This study compares monoaxial head locking screws (PHILOS© by Synthes) and a new generation of polyaxial locking screws (NCB-LE© by Zimmer) with respect to biomechanical stability.
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paper_title: The Mechanical Benefit of Medial Support Screws in Locking Plating of Proximal Humerus Fractures

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Background ::: The purpose of this study was to evaluate the biomechanical advantages of medial support screws (MSSs) in the locking proximal humeral plate for treating proximal humerus fractures.
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paper_title: Biomechanical effects of calcar screws and bone block augmentation on medial support in locked plating of proximal humeral fractures

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Abstract Background The objective of this study was to investigate the biomechanical effects of medial fracture gap augmentation in locked plating of an unstable 2-part proximal humeral fracture with calcar screws and insertion of a corticocancellous bone block. Furthermore the mechanical behavior of dynamic locking screws in the non-parallel arrangement of a proximal humeral plate was of interest. Methods Thirty-two fresh frozen humeri were randomized in four equal groups. An unstable 2-part fracture was fixed by locked plating in all specimens. The basic screw setup was supplemented by additional calcar screws in one group. Humeral head screws were replaced by dynamic locking screws in a second group. The third group featured an additional corticocancellous femoral head allograft. Assessment of stiffness was followed by cyclic loading and load to failure tests. Resulting stiffness, fracture gap deflection and ultimate load were compared utilizing Bonferroni corrected t-test for independent samples. Findings The mechanical effect of additional calcar screws was non-significant as compared to the basic screw configuration whereas bone block insertion significantly increased construct stiffness and failure load. The use of dynamic locking screws did not significantly reduce construct stiffness when compared to conventional locking screws. Interpretation Additional calcar screws alone did not improve the initial biomechanical properties of an unstable 2-part proximal humeral fracture model. However bone block augmentation appeared to be a reliable alternative of additional bony support by raising stiffness and failure load. Dynamic locking screws did not show their expected dynamic component when used in a non-parallel arrangement.
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paper_title: 45. BIOMECHANICAL ANALYSIS OF PROXIMAL HUMERAL FIXATION USING LOCKING PLATE FIXATION WITH AN INTRAMEDULLARY FIBULAR ALLOGRAFT

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Purpose: The purpose of this study is to compare two fixation methods for surgical neck proximal humeral fractures with medial calcar comminution: locking plate fixation alone and locking plate fixation with intramedullary allograft fibular bone peg augmentation. Method: Eight embalmed pairs of cadaveric specimens were utilized in this study. Dual energy X-ray absorptiometry (DXA) scans were initially performed to determine the bone density of the specimens. Surgical neck proximal humerus fractures were simulated in these specimens by creating a 1-centimeter wedge-shaped osteotomy at the level of the surgical neck to simulate medial calcar fracture comminution. Each pair of specimens had one arm randomly repaired with locking plate fixation, and the other arm repaired with locking plate fixation augmented with an intramedullary fibular autograft bone peg. The constructs were tested in bending to determine the failure loads, and initial stiffness using Digital Imaging Correlation (DIC) technology. The moment created by the rotator cuff was replicated by fixating the humeral head, and applying a point load to the distal humerus. A load was applied with a displacement rate of 4 mm/min, and was stopped approximately every 5 lbs to take a picture and record the load. This process was continued until failure of the specimens was obtained. Results: The intramedullary bone peg autograft increased the failure load of the constructs by 1.57±0.59 times (p = 0.026). Initial stiffness of the construct was also increased 3.13±2.10 times (p = 0.0079) with use of the bone peg. Conclusion: The stronger and stiffer construct provided by the addition of an intramedullary fibular allograft bone peg to locking plate fixation may help maintain reduction, and reduce the risk of fixation failure in surgical neck proximal humerus fractures with medial comminution.
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paper_title: Locking Plate Fixation with and without Inferomedial Screws for Proximal Humeral Fractures: A Biomechanical Study

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PURPOSE. To compare the efficacy of locking plate fixation with and without inferomedial screws in maintaining the reduction of a proximal humeral fracture. METHODS. 22 synthetic humerus models were used. A standardised 3-part proximal humeral fracture with a 4-mm wedge segment was created and fixed with a locking plate and screws with (n=11) and without (n=11) inferomedial screws. The intrafragmentary motion of the construct at 250, 500, 750, and 1000 cycles of 532 N loading, and the load to failure of the 2 groups were compared. RESULTS. Locking plate fixation with inferomedial screws reduced the mean intrafragmentary motion in all cycles (p<0.01) and increased the load to failure (1452 N vs. 1159 N, p<0.001), compared to fixation without inferomedial screws. CONCLUSION. Additional inferomedial screws provide medial column support for fracture healing. This may reduce intrafragmentary motion and thus implant complications resulting from varus malalignment such as screw perforation or loss of reduction.
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paper_title: The biomechanical performance of locking plate fixation with intramedullary fibular strut graft augmentation in the treatment of unstable fractures of the proximal humerus

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We evaluated the biomechanical properties of two different methods of fixation for unstable fractures of the proximal humerus. Biomechanical testing of the two groups, locking plate alone (LP), and locking plate with a fibular strut graft (LPSG), was performed using seven pairs of human cadaveric humeri. Cyclical loads between 10 N and 80 N at 5 Hz were applied for 1,000,000 cycles. Immediately after cycling, an increasing axial load was applied at a rate of displacement of 5 mm/min. The displacement of the construct, maximum failure load, stiffness and mode of failure were compared. The displacement was significantly less in the LPSG group than in the LP group (p = 0.031). All maximum failure loads and measures of stiffness in the LPSG group were significantly higher than those in the LP group (p = 0.024 and p = 0.035, respectively). In the LP group, varus collapse and plate bending were seen. In the LPSG group, the humeral head cut out and the fibular strut grafts fractured. No broken plates or screws were seen in either group. We conclude that strut graft augmentation significantly increases both the maximum failure load and the initial stiffness of this construct compared with a locking plate alone.
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paper_title: The Role of Medial Comminution and Calcar Restoration in Varus Collapse of Proximal Humeral Fractures Treated with Locking Plates

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Background: Proximal humeral fractures that are treated with locked plate constructs remain susceptible to collapse into a varus position. The objectives of the present study were to examine how medial comminution affects fracture stability and to determine the effect of calcar fixation on osteosynthesis stability. ::: ::: Methods: Eleven matched pairs of cadaveric humeri were osteotomized to create standard three-part fractures involving the surgical neck and the greater tuberosity. Five matched pairs were randomly assigned to have the medial calcar region remain intact. Six matched pairs had removal of a 10-mm medially based wedge of bone to simulate medial comminution. All fractures were stabilized in a uniform fashion with a proximal humeral locking plate. The constructs were secured, and the superior portion of the humeral head was subjected to compressive loading to induce varus collapse. Load-to-failure and energy-to-failure values along with stiffness and displacement at the time of failure were determined. ::: ::: Results: Medial comminution decreased the mean load to failure by 48% (523 N) (p = 0.015) and the mean energy to failure by 44% (2009 Nmm) (p = 0.013). The use of calcar screw fixation increased the mean load to failure by 31% (219 N) (p = 0.002) and the mean energy to failure by 44% (1279 Nmm) (p = 0.006). ::: ::: Conclusions: Medial comminution significantly decreased the stability of proximal humeral fracture fixation constructs. Calcar restoration with screw fixation significantly improved the stability of repaired fractures in cadaveric specimens. ::: ::: Clinical Relevance: The data suggest that medial comminution is a predictor of poor stability of proximal humeral fractures and that stability may be improved through calcar restoration.
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paper_title: Medial support by fibula bone graft in angular stable plate fixation of proximal humeral fractures: an in vitro study with synthetic bone.

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BACKGROUND ::: Failure to achieve stable fixation with medial support in proximal humeral fractures can result in varus malalignment and cut-through of the proximal screws. The purpose of this study was to investigate the influence of an intramedullary fibula bone graft on the biomechanical properties of proximal humeral fractures stabilized by angular stable plate fixation in a bone model under cyclic loading. ::: ::: ::: METHODS ::: Two fixation techniques were tested in 20 composite analog humeri models. In group F- (n = 10), fractures were fixed by an anatomically formed locking plate system. In group F+ (n = 10), the same fixation system was used with an additional fibular graft model with a length of 6 cm inserted in an intramedullary manner. Active abduction was simulated for 400 cycles by use of a recently established testing setup. Fragment gap distance was measured, and thereby, intercyclic motion, fragment migration, and residual plastic deformation were determined. ::: ::: ::: RESULTS ::: The addition of a fibular graft to the fixation plate led to 5 times lower intercyclic motion, 2 times lower fragment migration, and 2 times less residual plastic deformation. Neither screw pullout, cut-through, nor implant failure was observed. ::: ::: ::: CONCLUSION ::: Medial support with an intramedullary fibular graft in an angular stable fixation of the proximal humerus in vitro increases overall stiffness of the bone-implant construct and reduces migration of the humeral head fragment. This technique might provide a useful tool in the treatment of displaced proximal humeral fractures, especially when there is medial comminution.
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paper_title: Indirect Medial Reduction and Strut Support of Proximal Humerus Fractures Using an Endosteal Implant

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Fractures of the proximal humerus, particularly in osteoporotic bone, are still frequently referred to as unsolved fractures. The recent explosion of locking plate technology has included these fractures, but it appears that laterally placed locking plates may not be as predictable as hoped. Medial column mechanical support of these fractures may play a significant role in the ultimate stability of fixation during rehabilitation until healing occurs. We have devised a technique of using a segment of fibula allograft, placed endosteally and incorporated into the locking construct, to aid in the reduction and restoration of the mechanical integrity of the medial column of the proximal humerus.
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paper_title: The importance of medial support in locked plating of proximal humerus fractures.

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Objectives: The purpose of this study was to determine what factors influence the maintenance of fracture reduction after locked plating of proximal humerus fractures, and particularly the role of medial column support. Setting: University medical center. Intervention: Thirty-five patients who underwent locked plating for a proximal humerus fracture were followed up until healing. For the initial and final radiographs, 2 lines were drawn perpendicular to the shaft of the plate, one at the top of the plate and one at the top of the humeral head, and the distance between them was measured as an indicator of loss of reduction. Medial support was considered to be present if the medial cortex was anatomically reduced, if the proximal fragment was impacted laterally in the distal shaft fragment, or if an oblique locking screw was positioned inferomedially in the proximal humeral head fragment. Main Outcome Measurements: Multivariate linear regressions were performed to determine the effects that age, sex, fracture type, cement augmentation, and medial support had on loss of reduction. Results: The presence of medial support had a significant effect on the magnitude of subsequent reduction loss (P < 0.001). Age, sex, fracture type, or cement augmentation had no effect on maintenance of reduction. Eighteen patients were determined to have adequate mechanical medial support (+MS group), and the remaining 17 patients did not have medial support (-MS group). In the +MS group, the average loss of humeral head height was 1.2 mm, and 1 case of articular screw penetration occurred that required removal. In the - MS group (without an appropriately placed inferomedial oblique screw and either nonanatomic humeral head malreduction with lateral displacement of the shaft or medial comminution), loss of humeral height averaged 5.8 mm (P < 0.001). There were 5 cases in this group in which screw penetration of the articular surface occurred (P = 0.02), 2 of which required reoperation for removal. All fractures in both groups healed without delay, and none required revision to arthroplasty. Conclusions: Achieving mechanical support of the inferomedial region of the proximal humerus seems to be important for maintaining fracture reduction. Locked plates in general do not appear to be a panacea for these fractures and are unable to support the humeral head alone from a lateral tension-band position. However, there are several factors that are in the surgeon's control that may improve the mechanical environment. Achieving an anatomic or slightly impacted stable reduction, as well as meticulously placing a superiorly directed oblique locked screw in the inferomedial region of the proximal fragment, may achieve more stable medial column support and allow for better maintenance of reduction.
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paper_title: The Biomechanics of Locked Plating for Repairing Proximal Humerus Fractures With or Without Medial Cortical Support

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Background:Comminuted proximal humerus fracture fixation is controversial. Locked plate complications have been addressed by anatomic reduction or medial cortical support. The relative mechanical contributions of varus malalignment and lack of medial cortical support are presently assessed.Methods:F
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paper_title: Intramedullary cortical bone strut improves the cyclic stability of osteoporotic proximal humeral fractures

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Proximal humeral fractures treated with locking plate can fail due to varus collapse, especially in osteoporotic bone with medial cortex comminution. The use of an intramedullary strut together with locking plate fixation may strengthen fixation and provide additional medial support to prevent the varus malalignment. This study biomechanically investigates the influence of an intramedullary cortical bone strut on the cyclic stability of proximal humeral fractures stabilized by locking plate fixation in a cadaver model. Ten cadaveric humeri were divided into two groups statistically matched for bone density. Each specimen was osteotomized with 10 mm gap at the surgical neck. The non-augmented group stabilized with locking plate alone; in the augmented group, a locking plate was used combined with an intramedullary cortical bone strut. The strut was retrograded into the subchondral bone, and three humeral head screws were inserted into the strut to form a plate-screw-strut mechanism. The cyclic axial load was performed to 450 N for 6000 cycles and then loaded to failure. Construct stiffness, cyclic loading behavior and failure strength were analyzed to identify differences between groups. The augmented constructs were significantly stiffer than the non-augmented constructs during cycling. On average, the maximum displacements at 6000 cycles for non-augmented and augmented groups were 3.10 ± 0.75 mm and 1.7 ± 0.65 mm (p = 0.01), respectively. The mean peak-to-peak (inter cycle) displacement at 6000 cycles was about 2 times lower for the augmented group (1.36 ± 0.68 mm vs. 2.86 ± 0.51 mm). All specimens showed varus collapse combined with loss of screw fixation of the humeral head. The failure load of the augmented group was increased by 2.0 (SD = 0.41) times compared with the non-augmented group (p < 0.001). The stability and strength of the locking plate augmented with an intramedullary strut were significantly increased. For bone with poor quality, the subsidence of the locked screws led larger displacement, decreased the stability of the constructs, however, the plate-screw-strut mechanism provided more rigidity to stabilize the fixation. This study emphasized the importance of intramedullary support for the proximal humeral fractures fixed with a locked plate under cyclic loading, especially in bone with poor quality. This work is based on the results of cadaver model, further in vivo analysis is necessary to determine if the clinical results can be extrapolated from this data.
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paper_title: Proximal humeral fracture fixation: locking plate construct ± intramedullary fibular allograft.

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BACKGROUND ::: Locking plate constructs for proximal humeral fractures can fail due to varus collapse, especially in osteoporotic bone with medial cortex comminution. Augmentation, using a fibular allograft as an intramedullary bone peg, may strengthen fixation preventing varus collapse. This study investigated the ability of the augmented locking plate construct to withstand repetitive varus stresses relative to the nonaugmented construct. ::: ::: ::: MATERIALS AND METHODS ::: Proximal humeral fractures with medial comminution were simulated by performing wedge-shaped osteotomies at the surgical neck in cadaveric specimens. For each cadaver (n = 8), 1 humeral fracture was fixated with the locking plate construct alone and the other with the locking plate construct plus ipsilateral fibular autograft augmentation. The humeral head was immobilized and a repetitive, medially directed load was applied to the humeral shaft until construct collapse or until 25000 cycles were completed. ::: ::: ::: RESULTS ::: No augmented construct collapsed. In comparison, 6 of 8 nonaugmented constructs collapsed (P < .05). Collapse in the 6 nonaugmented constructs occurred after an average ±SD of 6604 ± 1984 cycles. Screw penetration of the articular surface was found in only 1 of the nonaugmented constructs. ::: ::: ::: CONCLUSION ::: Fibular allograft augmentation increased the ability of the locking plate to withstand repetitive varus loading. Clinically, this may assist proximal humeral fracture fixation in osteoporotic bone with medial cortex comminution.
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paper_title: Migration of pins used in operations on the shoulder.

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Migration of pins used in operations on the shoulder. F Lyons;C Rockwood; The Journal of Bone & Joint Surgery
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paper_title: Straining of the intact and fractured proximal humerus under physiological-like loading.

paper_content:

Surgical treatment of proximal humeral fractures remains challenging in elderly patients, primarily due to insufficient implant fixation. Both bone quality and physiological-like loading conditions are commonly overlooked during pre-clinical in vitro evaluation. However, this knowledge is necessary in order to improve surgical treatment of the proximal humerus and the mechanical behavior of implants, particularly in patients with complex fractures and weak bone stock. We hypothesize that the bone quality has a high influence on the bone straining, independent of the arm position. The goal of this study was to determine the straining of the intact and fractured proximal humerus under physiological-like loading conditions. Furthermore, the impact of augmentation on tissue straining was evaluated. Two representative humeri were selected for this study, one osteoporotic and one reference quality, and scanned using both QCT and DEXA (average DEXA value=0.26 and 0.49 g/cm2 respectively). Subcaptial defects were generated, then stabilized with a plate prior to mechanical stiffness testing. From the QCT data, finite element models were generated and the in vitro stiffness tests analytically simulated. Under physiological-like loading conditions, the straining of the bone and implant were analyzed for 0 degrees, 90 degrees forward flexion, and 90 degrees abduction. Maximal strain values were found for the intact and fractured bone at 90 degrees abduction. This study demonstrates that the straining in a fractured bone of poor quality leads to considerably higher bone strains (up to +30%) than in a more healthy bone. Augmentation of a central void under physiological-like loading with commercial cement led to mechanical failure at the bone-cement interface. New concepts for the surgical treatment of complex fractures of the proximal humerus should take bone distribution into account and thereby allow effective treatment of fractures in osteoporotic patients. The ultimate salvage procedure of augmentation has mechanical limitations as long as current cement materials are used in osteoporotic patients.
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paper_title: [Migration of Kirschner wires after surgical stabilization of injuries in the area of the shoulder--4 case reports].

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Internal fixation is recommended for displaced and unstable fractures of the lateral clavicle and fractures involving the proximal humerus. Kirschner wires, although recommended in the orthopedic literature bear the risk of wire breakage and migration. 4 cases with serious and potentially hazardous complications are presented. All reported complications occurred years after the operative treatment without clinical symptoms. Regular postoperative follow-ups and early hardware removal after fracture healing is recommended.
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paper_title: Magnitudes of local stress and strain along bony surfaces predict the course and type of fracture healing

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Abstract A new quantitative tissue differentiation theory which relates the local tissue formation in a fracture gap to the local stress and strain is presented. Our hypothesis proposes that the amounts of strain and hydrostatic pressure along existing calcified surfaces in the fracture callus determine the differentiation of the callus tissue. The study compares the local strains and stresses in the callus as calculated from a finite element model with histological findings from an animal fracture model. The hypothesis predicts intramembranous bone formation for strains smaller approximately ±5% and hydrostatic pressures smaller than ±0.15 MPa. Endochondral ossification is associated with compressive pressures larger than about −0.15 MPa and strains smaller than ±15%. All other conditions seemed to lead to connective tissue or fibrous cartilage. The hypothesis enables a better understanding of the complex tissue differentiation seen in histological images and the mechanical conditions for healing delayed healing or nonunions.
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paper_title: Mechanical evaluation of a new minimally invasive device for stabilization of proximal humeral fractures in elderly patients: a cadaver study.

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BACKGROUND ::: Treatment of proximal humerus fractures in elderly patients is challenging because of reduced bone quality. We determined the in vitro characteristics of a new implant developed to target the remaining bone stock, and compared it with an implant in clinical use. ::: ::: ::: METHODS ::: Following osteotomy, left and right humeral pairs from cadavers were treated with either the Button-Fix or the Humerusblock fixation system. Implant stiffness was determined for three clinically relevant cases of load: axial compression, torsion, and varus bending. In addition, a cyclic varus-bending test was performed. ::: ::: ::: RESULTS ::: We found higher stiffness values for the humeri treated with the ButtonFix system--with almost a doubling of the compression, torsion, and bending stiffness values. Under dynamic loading, the ButtonFix system had superior stiffness and less K-wire migration compared to the Humerusblock system. ::: ::: ::: INTERPRETATION ::: When compared to the Humerusblock design, the ButtonFix system showed superior biomechanical properties, both static and dynamic. It offers a minimally invasive alternative for the treatment of proximal humerus fractures.
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paper_title: Proximal humeral fractures: what is semi-rigid? Biomechanical properties of semi-rigid implants, a biomechanical cadaver based evaluation

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INTRODUCTION ::: Proximal humerus fractures remain challenging especially in the elderly. Biomechanical data put semi-rigid implants in favour of osteopenic or osteoporotic situation. Little surgical side damage is associated with a minimal invasive approach of these implants. The aim of this study was to evaluate the mechanical properties of three such implants. ::: ::: ::: MATERIAL AND METHODS ::: Fresh frozen cadaver specimens were mounted as proposed by the distributors. Three different implants were used: LCP-PH (locking compression plate proximal humerus, Synthes, Austria), HB (humerus block, Synthes, Austria), and IMC (intramedullary claw, ITS, Austria). Subcapital fracture was simulated by resecting a 5 mm gap. All specimens were comparable in "B" (one), "M" (ineral) and "D" (ensity). Four load cases were tested: varus bending, medial shearing and axial torque. A cyclic test (1,000 cycles) was performed in the first load case (varus stress) for all three implants. ::: ::: ::: RESULTS ::: The LCP-PH was the most rigid in all three load cases, always followed by the HB. The IMC was the most elastic device with almost immeasurable values in axial torque. In the cyclic setting, the load reduction of the HB followed by the LCP-PH was significantly better than that for the IMC. ::: ::: ::: CONCLUSION ::: The differences in stiffness are varying tremendously. The IMC is the implant with the lowest stiffness in all load cases and the highest load reduction. New "semi-rigids" claim good clinical performance, yet prospective clinical studies have to prove this. It is unlikely that the IMC can maintain fracture reduction in fracture situations of complex nature (no ligamentotaxis).
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paper_title: [Are angle-fixed implants with elastic properties advantageous for the internal fixation of proximal humerus fractures?].

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There is a recent interest for the use of angle-fixed plates in the management of proximal humerus fractures. Rigid implants might be associated with an increased risk of cutting-out. In order to analyse the potential beneficial effects of the implant elasticity on fracture fixation, the biomechanical properties of a rigid and an elastic angle-fixed plating system were assessed in an experimental study. An unstable fracture of the surgical neck was created in 8 pairs of human humeri. Specimens were subjected to axial loading and torque. Stiffness, subsidence and load to failure were assessed. The implant with elastic properties was characterized by a lower torsional stiffness and a higher subsidence during axial loading and torque. This implant failed at lower loads than the rigid implant did. Elastic implant properties of angle-fixed plates have shown not to be advantageous for the management of fractures of the proximal humerus.
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paper_title: Cyclical micromovement and fracture healing.

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We studied 56 patients with fractures of the tibial shaft in a multicentre prospective randomised trial of three methods of external fixation. Group I was treated with a fixator which was unlocked at 4 to 6 weeks to allow free axial compression (axial dynamisation) with weight-bearing. Group II was treated with a fixator that was similarly unlocked at 4 to 6 weeks but included a small silicone spring which on weight-bearing could be compressed by up to 2 mm. this spring returns to its original length on cessation of weight-bearing thus allowing cycles of motion of up to 2 mm. Group III had a spring fixator like group II, but it was unlocked from the start to allow cyclical micromovement as soon as weight-bearing began. Fracture healing was monitored by the measurement of fracture stiffness. We defined healing as achieving a stiffness of 15 Nm per degree. The mean time was 14.1 weeks in group I, 15.9 weeks in group II, and 19.3 weeks in group III. The difference between groups was statistically significant (p = 0.004). The 95% confidence intervals for the average delay in healing with early cyclical micromovement (group III) as compared with later axial dynamisation (group I) was 1.8 to 8.7 weeks. The healing time in patients whose cyclical micromovement was delayed for 4 to 6 weeks (group II) was between these two extremes, but the differences from either of the other groups could have been due to patient selection. In the patients who completed the full trial, there were pin-track infections in over 60% of those in the cyclical micromovement groups compared with 20% in the axial dynamisation group (p = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)
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paper_title: UNSTABLE TROCHANTERIC FRACTURES AUGMENTED WITH CALCIUM PHOSPHATE CEMENT. A prospective randomized study using radiostereometry to measure fracture stability

paper_content:

Unstable trochanteric fractures augmented with calcium phosphate cement. A prospective randomized study using radiostereometry to measure fracture stability
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paper_title: Straining of the intact and fractured proximal humerus under physiological-like loading.

paper_content:

Surgical treatment of proximal humeral fractures remains challenging in elderly patients, primarily due to insufficient implant fixation. Both bone quality and physiological-like loading conditions are commonly overlooked during pre-clinical in vitro evaluation. However, this knowledge is necessary in order to improve surgical treatment of the proximal humerus and the mechanical behavior of implants, particularly in patients with complex fractures and weak bone stock. We hypothesize that the bone quality has a high influence on the bone straining, independent of the arm position. The goal of this study was to determine the straining of the intact and fractured proximal humerus under physiological-like loading conditions. Furthermore, the impact of augmentation on tissue straining was evaluated. Two representative humeri were selected for this study, one osteoporotic and one reference quality, and scanned using both QCT and DEXA (average DEXA value=0.26 and 0.49 g/cm2 respectively). Subcaptial defects were generated, then stabilized with a plate prior to mechanical stiffness testing. From the QCT data, finite element models were generated and the in vitro stiffness tests analytically simulated. Under physiological-like loading conditions, the straining of the bone and implant were analyzed for 0 degrees, 90 degrees forward flexion, and 90 degrees abduction. Maximal strain values were found for the intact and fractured bone at 90 degrees abduction. This study demonstrates that the straining in a fractured bone of poor quality leads to considerably higher bone strains (up to +30%) than in a more healthy bone. Augmentation of a central void under physiological-like loading with commercial cement led to mechanical failure at the bone-cement interface. New concepts for the surgical treatment of complex fractures of the proximal humerus should take bone distribution into account and thereby allow effective treatment of fractures in osteoporotic patients. The ultimate salvage procedure of augmentation has mechanical limitations as long as current cement materials are used in osteoporotic patients.
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paper_title: Biomechanical Evaluation of Locking Plate Fixation of Proximal Humeral Fractures Augmented With Calcium Phosphate Cement

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OBJECTIVES ::: To evaluate the influence of calcium phosphate cement augmentation on failure of locking plate fixation of proximal humeral fracture fixation in a cadaveric fracture model. ::: ::: ::: METHODS ::: A 5-mm wedge osteotomy was created in each of 11 paired fresh-frozen human cadaveric humeri (age > 65 years). Specimens were randomly assigned to receive either locked plate fixation (group 1) or locked plate fixation with cement augmentation (group 2). Constructs were tested for axial stiffness, load to failure, and failure mode using a material testing machine. ::: ::: ::: RESULTS ::: Cement-augmented specimens resisted higher loads (1936 ± 609 N) in comparison to nonaugmented specimens (1373 ± 590 N) (P = 0.01). In group 1, varus displacement and glenohumeral screw perforation occurred in all cases. Varus displacement occurred in 2 cases in group 2, whereas glenohumeral screw perforation did not occur in any of the cases. Cement augmentation led to a significant increase in axial stiffness (P = 0.04). ::: ::: ::: CONCLUSIONS ::: Calcium phosphate cement-augmented locking plates enhanced fixation stability in proximal humeral fractures and reduced glenohumeral screw perforation in this 2-part cadaveric model. The ultimate advantage of this method remains to be determined in vivo.
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paper_title: Mechanical Assessment of Local Bone Quality to Predict Failure of Locked Plating in a Proximal Humerus Fracture Model

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The importance of osteoporosis in proximal humerus fractures is well recognized. However, the local distribution of bone quality in the humeral head may also have a significant effect because it remains unclear in what quality of bone screws of standard implants purchase. The goal of this study was to investigate whether the failure of proximal humerus locked plating can be predicted by the DensiProbe (ARI, Davos, Switzerland). A 2-part fracture with metaphyseal impaction was simulated in 12 fresh-frozen human cadaveric humeri. Using the DensiProbe, local bone quality was determined in the humeral head in the course of 6 proximal screws of a standard locking plate (Philos; Synthes GmbH, Solothurn, Switzerland). Cyclic mechanical testing with increasing axial loading until failure was performed. Bone mineral density (BMD) significantly correlated with cycles until failure. Head migration significantly increased between 1000 and 2000 loading cycles and significantly correlated with BMD after 3000 cycles. DensiProbe peak torque in all screw positions and their respective mean torque correlated significantly with the BMD values. In 3 positions, the peak torque significantly correlated with cycles to failure; here BMD significantly influenced mechanical stability. The validity of the DensiProbe was proven by the correlation between its peak torque measurements and BMD. The correlation between the peak torque and cycles to failure revealed the potential of the DensiProbe to predict the failure of locked plating in vitro. This method provides information about local bone quality, potentially making it suitable for intraoperative use by allowing the surgeon to take measures to improve stability.
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paper_title: Screw augmentation reduces motion at the bone-implant interface: a biomechanical study of locking plate fixation of proximal humeral fractures.

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BACKGROUND ::: Shear forces at the bone-implant interface lead to a loss of reduction after locking plate fixation of proximal humeral fractures. The aim of the study was to analyze the roles of medial support screws and screw augmentation in failure loads and motion at the bone-implant interface after locking plate fixation of proximal humeral fractures. ::: ::: ::: METHODS ::: Unstable 3-part fractures were simulated in 6 pairs of cadaveric humeri and were fixed with a DiPhos-H locking plate (Lima Corporate, Udine, Italy). An additional medial support screw was implanted in 1 humerus of every donor. The opposite humerus was stabilized with a medial support screw and additional bone cement augmentation of the 2 anteriorly directed head screws. Specimens were loaded in the varus bending position. Stiffness, failure loads, plate bending, and the motion at the bone-implant interface were evaluated using an optical motion capture system. ::: ::: ::: RESULTS ::: The mean load to failure was 669 N (standard deviation [SD], 117 N) after fixation with medial support screws alone and 706 N (SD, 153 N) after additional head screw augmentation (P = .646). The initial stiffness was 453 N/mm (SD, 4.16 N/mm) and 461 N/mm (SD, 64.3 N/mm), respectively (P = .594). Plate bending did not differ between the 2 groups. However, motion at the bone-implant interface was significantly reduced after head screw augmentation (P < .05). ::: ::: ::: CONCLUSION ::: The addition of bone cement to augment anteriorly directed head screws does not increase stiffness and failure loads but reduces motion at the bone-implant interface. Thus, the risk of secondary dislocation of the head fragment may be reduced.
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paper_title: Norian SRS Versus Functional Treatment in Redisplaced Distal Radial Fractures: A Randomized Study in 20 Patients

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We compared the use of Norian SRS, an injectable calcium phosphate bone cement, with functional treatment of redisplaced distal radial fractures in a prospective randomized study of 20 patients. The redisplaced fractures were either rereduced and stabilized by Norian SRS, or the displaced position was accepted and was not rereduced. All wrists were immobilized in a short-arm dorsal splint for 1 week, followed by a removable splint for another 3 weeks. The chosen primary effect variable was grip strength at 7 weeks, and this did not differ between the two treatment groups. The clinical results at 6 months in both groups were similar. We conclude that aggressive treatment of redisplaced fractures of the distal radius may be unnecessary in most women aged 50 years or more.
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paper_title: Biomechanical in vitro assessment of screw augmentation in locked plating of proximal humerus fractures

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Abstract Introduction Proximal humerus fracture fixation can be difficult because of osteoporosis making it difficult to achieve stable implant anchorage in the weak bone stock even when using locking plates. This may cause implant failure requiring revision surgery. Cement augmentation has, in principle, been shown to improve stability. The aim of this study was to investigate whether augmentation of particular screws of a locking plate aimed at a region of low bone quality is effective in improving stability in a proximal humerus fracture model. Materials and methods Twelve paired human humerus specimens were included. Quantitative computed tomography was performed to determine bone mineral density (BMD). Local bone quality in the direction of the six proximal screws of a standard locking plate (PHILOS, Synthes) was assessed using mechanical means (DensiProbe™). A three-part fracture model with a metaphyseal defect was simulated and fixed with the plate. Within each pair of humeri the two screws aimed at the region of the lowest bone quality according to the DensiProbe™ were augmented in a randomised manner. For augmentation, 0.5 ml of bone cement was injected in a screw with multiple outlets at its tip under fluoroscopic control. A cyclic varus-bending test with increasing upper load magnitude was performed until failure of the screw–bone fixation. Results The augmented group withstood significantly more load cycles. The correlation of BMD with load cycles until failure and BMD with paired difference in load cycles to failure showed that augmentation could compensate for a low BMD. Discussion and conclusion The results demonstrate that augmentation of screws in locked plating in a proximal humerus fracture model is effective in improving primary stability in a cyclic varus-bending test. The augmentation of two particular screws aimed at a region of low bone quality within the humeral head was almost as effective as four screws with twice the amount of bone cement. Screw augmentation combined with a knowledge of the local bone quality could be more effective in enhancing the primary stability of a proximal humerus locking plate because the effect of augmentation can be exploited more effectively limiting it to the degree required.
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paper_title: Use of an injectable calcium phosphate bone cement in the treatment of tibial plateau fractures: a prospective study of twenty-six cases with twenty-month mean follow-up.

paper_content:

OBJECTIVE ::: To evaluate the potential benefit of a new injectable mineral bone cement (Norian SRS, Cupertino, CA, USA) for the treatment of tibial plateau fractures OTA types 41.B2-B3 and C3. ::: ::: ::: DESIGN ::: Prospective study with established protocol. ::: ::: ::: SETTING ::: University hospital; university teaching hospital. ::: ::: ::: PATIENTS ::: Twenty-six patients gave informed consent to participate in this study and were available for follow-up examinations. All patients had sustained intraarticular tibial plateau fracture types OTA B2-B3 and C3. All cases were followed with a mean follow-up time of 19.7 months (6 to 36 months, median eighteen months). ::: ::: ::: INTERVENTION ::: Twenty-five cases were treated with open reduction, osteosynthesis with screws or plate, and injection of Norian SRS in the subchondral bone defect. One case had closed reduction, screw osteosynthesis, and percutaneous cement injection. ::: ::: ::: MAIN OUTCOME MEASUREMENTS ::: Radiographs in two planes were evaluated prospectively at six, twelve, and twenty-six weeks postoperatively and at last follow-up using Rasmussen's radiologic score. Clinical parameters were measured at the same time intervals using Lysholm's and Tegner's knee scores. ::: ::: ::: RESULTS ::: Two cases required early wound revisions because of sterile drainage. Two cases developed partial loss of reduction of the fracture between four and eight weeks after surgery, requiring revision surgery in one case (total complication rate 15.3 percent). No other patients had complications, and all other fractures healed without any displacement. The high mechanical strength of the cement allowed early weight bearing after a mean postoperative period of 4.5 weeks (1 to 6 weeks). ::: ::: ::: CONCLUSIONS ::: An injectable mineral bone cement with high initial mechanical strength was used to fill bone defects in unstable tibial plateau fractures with good success. This material offers new perspectives in the treatment of tibial plateau fractures.
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paper_title: Biomechanical comparison of an angular stable plate with augmented and non-augmented screws in a newly developed shoulder test bench.

paper_content:

BACKGROUND ::: The proximal humeral fracture is one of the most common fractures. Although there are a number of treatment options available, the clinical outcomes in geriatric patients are still unsatisfactory. Therefore, the aim of this study was to investigate the biomechanical behaviour of an angular stable plate with either augmented or non-augmented screws using two different fracture models in a shoulder test bench with active muscle forces. ::: ::: ::: METHODS ::: Six paired fresh-frozen humeri were loaded into a shoulder test bench simulating ab- and adduction between 15 and 45° induced by active muscle forces. The bone mineral density was measured by a quantitative CT. A two-part fracture model (stable and an unstable) was used to investigate the different biomechanical behaviours of the PHILOS plate, either utilising cannulated screws, allowing in situ augmentation, or without utilising augmented screws. Four screws were augmented with 0.5ml PMMA cement. ::: ::: ::: FINDINGS ::: The in vitro-measured resulting forces in the glenoid fossa were comparable to the in vivo forces generated in shoulder arthroplasties. Under stable conditions, the per cycle motion and varus impaction tilting showed no significant difference. In the unstable state, the augmented group showed a maximum of 0.81° per cycle motion and a maximum varus impaction of -1.46° compared to the non-augmented maximum of 2.31° per cycle motion and maximum varus impaction of -4.26° (P<0.05). ::: ::: ::: INTERPRETATION ::: In an unstable fracture model under dynamic testing conditions, augmentation leads to a decreased per cycle motion and varus impaction of the humeral head.
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paper_title: Augmentation of pedicle screw stability with calcium sulfate cement in osteoporotic sheep: biomechanical and screw-bone interfacial evaluation.

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Study Design Augmentation of pedicle screws with calcium sulfate cement (CSC) was performed in osteoporotic sheep. Biomechanical tests, micro-computed tomography (CT) analysis, and histological observation were performed. Objective To investigate the long-term biomechanical performance of pedicle screws augmented with CSC in vivo and evaluated the screw-bone interfacial bonding with micro-CT and histological techniques. Summary of Background Data There is little information on the long-term biomechanical performance and screw-bone interfacial bonding of pedicle screws augmented with CSC in osteoporosis in vivo. Methods Twelve months after ovariectomy, bilateral pedicles of lumbar vertebrae (L1 to L5) of 6 female sheep were fixed with pedicle screws. One pedicle of each vertebral body was treated with a screw augmented with CSC (CSC group) and the contralateral pedicle was treated with a screw without any augmentation (control group). Three months later, the sheep were killed and biomechanical tests, micro-CT analysis, and histological observation were conducted on the isolated specimen vertebrae. Results Twelve months after ovariectomy, animal model of osteoporosis was established successfully. Both the axial and vertical stabilities of the pedicle screws in CSC group were significantly enhanced compared with those in the control group (P Conclusions CSC can significantly improve screw-bone interfacial bonding and strengthen the long-term stability of pedicle screws in osteoporotic sheep. Augmentation with CSC may be a potentially useful method to increase the stability of pedicle screws in patients with osteoporosis.
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paper_title: BIOMECHANICAL EVALUATION OF PROXIMAL HUMERAL FRACTURE FIXATION SUPPLEMENTED WITH CALCIUM PHOSPHATE CEMENT

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Background: Proximal humeral fractures are common injuries, and numerous surgical methods have been described for their treatment. The biomechanical characteristics of various internal fixation devices that are used to treat these fractures have not been extensively studied, nor has the potential beneficial effect of calcium phosphate cement supplementation. Methods: We used a cadaveric three-part proximal humeral osteotomy model to perform a biomechanical evaluation of three types of internal fixation devices: a cloverleaf plate, an angled blade-plate, and Kirschner wires. The effect of supplementing the fixation with SRS (Skeletal Repair System) calcium phosphate cement was evaluated as well. Eighteen pairs of fresh-frozen humeri were obtained, and the bone-mineral density of each specimen was measured. In each pair, one specimen was secured with internal fixation alone and the contralateral specimen was secured with internal fixation combined with calcium phosphate cement. The specimens were tested cyclically in abduction and in external rotation for 250 cycles to evaluate interfragmentary motion. The specimens were then loaded to failure in external rotation to measure torsional load to failure and torsional stiffness. Results: Overall, there were no significant differences between the specimens treated with the blade and cloverleaf plates, whereas the specimens treated with Kirschner wires demonstrated more interfragmentary motion, less stiffness, and lower torque to failure. In general, supplementation with calcium phosphate cement led to significant improvements in the mechanical performance of all three forms of internal fixation as demonstrated by a significant decrease in interfragmentary motion, a significant increase in torque to failure, and a significant increase in torsional stiffness. The addition of calcium phosphate cement increased the stiffness of even the most osteoporotic specimens to levels that were higher than those of the most osteodense specimens that had been treated with internal fixation alone. Conclusion: The initial biomechanical properties of internal fixation as measured with use of a proximal humeral osteotomy model and three methods of fixation were significantly improved by the addition of calcium phosphate cement. Clinical Relevance: The addition of calcium phosphate cement may augment the mechanical characteristics of internal fixation of difficult, three-part proximal humeral fractures. The ability to stabilize the interface between the implant and cancellous bone, particularly in the presence of osteopenia, may make calcium phosphate cement a valuable clinical tool in the treatment of these difficult fractures.
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paper_title: The effect of in situ augmentation on implant anchorage in proximal humeral head fractures

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Abstract Introduction Fracture fixation in patients suffering from osteoporosis is difficult as sufficient implant anchorage is not always possible. One method to enhance implant anchorage is implant/screw augmentation with PMMA-cement. The present study investigated the feasibility of implant augmentation with PMMA-cement to enhance implant anchorage in the proximal humerus. Materials and methods A simulated three part humeral head fracture was stabilised with an angular stable plating system in 12 pairs of humeri using six head screws. In the augmentation group the proximal four screws were treated with four cannulated screws, each augmented with 0.5 ml of PMMA-cement, whereas the contra lateral side served as a non-augmented control. Specimens were loaded in varus-bending or axial-rotation using a cyclic loading protocol with increasing load magnitude until failure of the osteosynthesis occurred. Results Augmented specimens showed a significant higher number of load cycles until failure than non-augment specimens (varus-bending: 8516 (SD 951.6) vs. 5583 (SD 2273.6), P = 0.014; axial-rotation: 3316 (SD 348.8) vs. 2050 (SD 656.5), P = 0.003). Non-augmented specimens showed a positive correlation of load cycles until failure and measured bone mineral density (varus-bending: r = 0.893, P = 0.016; axial-rotation: r = 0.753, P = 0.084), whereas no correlation was present in augmented specimens (varus-bending: r = 0,258, P = 0.621; axial-rotation r = 0.127, P = 0.810). Conclusion These findings suggest that augmentation of cannulated screws is a feasible method to enhance implant/screw anchorage in the humeral head. The improvement of screw purchase is increasing with decreasing bone mineral density.
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paper_title: functional outcome and complications following PHILOS plate fixation proximal humeral fractures

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Objectives: Proximal humeral fractures account for approximately 5% of all fractures. New plating techniques have been developed to improve stability. The purpose of this study was to evaluate functional outcome following plate fixation with the Proximal Humeral Internal Locking System (PHILOS) and to analyze potential implant-related complications. ::: Methods: The PHILOS plate was used for internal fixation of displaced proximal humeral fractures in 28 patients (20 females, 8 males; mean age 60.7±12.9 years). Fractures were caused by low-energy trauma (fall from standing height) in 21 patients, and by an accident while skiing or cycling in seven patients. Involvement was on the right in 16 cases and on the left in 12 cases. According to the Neer classification, 8, 12, and 8 patients had displaced 2-, 3-, or 4-part fractures, respectively. All patients received a similar physical therapy program following internal fixation with the PHILOS plate. The patients were assessed clinically and radiographically after a mean follow-up of 25.2±11.8 months. Functional outcome was assessed using the Constant-Murley score adjusted for age and gender. Range of motion and shoulder abduction strength were measured. The patients were also evaluated with the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire and a visual analog scale (VAS). Complications during the follow-up period were recorded. ::: Results: Twenty fractures (71.4%) healed in good anatomical position. At the end of the follow-up period, the mean Constant-Murley score was 57.9±21.7, and the mean age- and gender-adjusted Constant-Murley score was 67.5±23.6. The results were excellent or good in 16 patients (57.1%), moderate in one patient (3.6%), and poor in 11 patients (39.3%). The mean DASH and VAS scores were 28.3±24.3 and 75.4±21.2, respectively. Eleven complications (39.3%) were seen during the follow-up period. Reoperation was required in eight patients (72.3%). Complications included avascular necrosis of the humeral head in two patients (7.2%), subacromial impingement in six patients (21.4%), loosening of a locking head screw in one patient (3.6%), and transiently decreased radial nerve sensation in two patients (7.2%). Subacromial impingement was mainly caused by the superior plate position. ::: Conclusion: Our results demonstrate that the PHILOS plate provides sufficient fracture stabilization in the treatment of proximal humeral fractures of elderly patients.
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paper_title: Biomechanical analysis of a novel locking plate with smooth pegs versus a conventional locking plate with threaded screws for proximal humerus fractures.

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BACKGROUND ::: Repair of proximal humeral fractures with locking plates has greatly improved outcomes. However, an alarming rate of complications including screw cutout and impingement under the acromion has recently been reported. A novel locking plate with smooth pegs was developed to reduce these risks. The purpose of this study was to compare these 2 fixation methods with a cadaveric biomechanical study. ::: ::: ::: MATERIALS AND METHODS ::: Fourteen pairs of cadaveric proximal humeri (mean age, 77 years) were harvested, and bone density was measured. Osteosynthesis was performed on each pair using either a locking plate with threaded screws (TS group) or smooth pegs (SP group) on the contralateral side. Seven pairs of humeri were tested for cyclic bending, and 7 pairs for cyclic torsional evaluation: TS bending, SP bending, TS torsion, and SP torsion. The bending protocol consisted of cyclically loading to a maximum of 7.5 Nm bending moment for 10,000 cycles. The torsion protocol consisted of ±2 Nm of axial torque for 10,000 cycles. Surgical neck fractures were simulated by excising a 10-mm wedge of bone. ::: ::: ::: RESULTS ::: No implant failure or screw cutout was observed in any of the groups tested. Under bending loads, mean displacement of the distal fragment was significantly less for the SP group than that for the TS group over 5,000 cycles. In torsion tests, no significant differences were observed between the 2 fixation methods. ::: ::: ::: DISCUSSION ::: The SP group demonstrated superior biomechanical characteristics to the TS group in regards to cyclic bending.
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paper_title: Proximal humeral fracture fixation: a biomechanical comparison of two constructs.

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BACKGROUND ::: Different options exist for stabilizing proximal humeral fractures. This study compared the mechanical stability of 2 common proximal humeral fixation plates in bending and torsion. ::: ::: ::: METHODS ::: Tests were conducted on 40 synthetic and 10 matched pairs of cadaveric humeri (evenly fixed with DePuy S3 proximal humeral plating system [DePuy Orthopaedics, Warsaw, IN, USA] and Synthes proximal humerus locking compression plate [Synthes, Paoli, PA, USA]). Half of the humeri were tested by cantilevered bending in flexion, extension, varus, and valgus for 100 cycles of ±5 mm of displacement at 1 mm/s before loading to failure in varus. The other half were tested in torsion for 100 cycles of ±8° of rotational displacement at 1°/s before loading to failure in external rotation. ::: ::: ::: RESULTS ::: Peak cyclic loads for synthetic constructs were higher for DePuy plates than Synthes plates in varus and valgus (P < .0001), but a difference was not detected in extension (P > .40) or flexion (P = .0675). Peak cyclic loads for cadaveric constructs showed a significant difference in extension and flexion (Synthes > DePuy, P < .0001) and in varus (DePuy > Synthes, P < .05) but not in valgus (P > .10). Bending stiffness during varus failure testing was higher for DePuy plates than Synthes plates (P < .0001) for synthetic constructs. Regarding torsion of synthetic and cadaveric constructs, DePuy plates experienced higher peak cyclic torques over all cycles in both directions (P < .0001). For synthetic constructs, DePuy plates showed higher torsional stiffness in external failure than Synthes plates (P < .0001). ::: ::: ::: CONCLUSIONS ::: The DePuy plate was stiffer than the Synthes plate with varus and valgus bending, as well as in torsion. The Synthes plate tended to be stiffer in flexion and extension.
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paper_title: Biomechanical comparison of a proximal humeral locking plate using two methods of head fixation.

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HYPOTHESIS ::: Locking plates have emerged as the implant of choice for stabilization of proximal humeral fractures. The biomechanical properties of a locked plating system using smooth pegs vs threaded screws for fixation of the humeral head were compared to test the hypothesis that there would be no biomechanical difference between pegs and threaded screws. ::: ::: ::: MATERIALS AND METHODS ::: Sixteen pairs of fresh frozen cadaveric humeri were randomized to have a surgical neck gap osteotomy stabilized with a locked plate using threaded screws (n=8) or smooth pegs (n=8). The intact contralateral humerus served as a control. Each specimen was tested with simultaneous cyclic axial compression (40 Nm) and torsion (both +/-2 Nm and +/-5 Nm) for 6000 cycles. All specimens were loaded to failure. Interfragmentary motion and load-displacement curves were analyzed to identify differences between the groups. Our data were then compared to previously published forces across the glenohumeral joint to provide evidence based recommendations for postoperative use of the shoulder. ::: ::: ::: RESULTS ::: There was a statistically significant difference between test specimens and their paired control (P < .001) in cyclic testing and load to failure. Differences between the smooth pegs and threaded screws were not statistically significant. ::: ::: ::: DISCUSSION ::: There is no biomechanical difference between locked smooth pegs and locked threaded screws for proximal fragment fixation in an unstable 2-part proximal humeral fracture model. ::: ::: ::: CONCLUSION ::: Our study contributes to the published evidence evaluating forces across the glenohumeral joint and suggests that early use of the affected extremity for simple activities of daily living may be safe. Use of the arm for assisted ambulation requiring a crutch, cane, walker, or wheelchair should be determined on a case-by-case basis.
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paper_title: Biomechanical effects of calcar screws and bone block augmentation on medial support in locked plating of proximal humeral fractures

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Abstract Background The objective of this study was to investigate the biomechanical effects of medial fracture gap augmentation in locked plating of an unstable 2-part proximal humeral fracture with calcar screws and insertion of a corticocancellous bone block. Furthermore the mechanical behavior of dynamic locking screws in the non-parallel arrangement of a proximal humeral plate was of interest. Methods Thirty-two fresh frozen humeri were randomized in four equal groups. An unstable 2-part fracture was fixed by locked plating in all specimens. The basic screw setup was supplemented by additional calcar screws in one group. Humeral head screws were replaced by dynamic locking screws in a second group. The third group featured an additional corticocancellous femoral head allograft. Assessment of stiffness was followed by cyclic loading and load to failure tests. Resulting stiffness, fracture gap deflection and ultimate load were compared utilizing Bonferroni corrected t-test for independent samples. Findings The mechanical effect of additional calcar screws was non-significant as compared to the basic screw configuration whereas bone block insertion significantly increased construct stiffness and failure load. The use of dynamic locking screws did not significantly reduce construct stiffness when compared to conventional locking screws. Interpretation Additional calcar screws alone did not improve the initial biomechanical properties of an unstable 2-part proximal humeral fracture model. However bone block augmentation appeared to be a reliable alternative of additional bony support by raising stiffness and failure load. Dynamic locking screws did not show their expected dynamic component when used in a non-parallel arrangement.
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paper_title: 45. BIOMECHANICAL ANALYSIS OF PROXIMAL HUMERAL FIXATION USING LOCKING PLATE FIXATION WITH AN INTRAMEDULLARY FIBULAR ALLOGRAFT

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Purpose: The purpose of this study is to compare two fixation methods for surgical neck proximal humeral fractures with medial calcar comminution: locking plate fixation alone and locking plate fixation with intramedullary allograft fibular bone peg augmentation. Method: Eight embalmed pairs of cadaveric specimens were utilized in this study. Dual energy X-ray absorptiometry (DXA) scans were initially performed to determine the bone density of the specimens. Surgical neck proximal humerus fractures were simulated in these specimens by creating a 1-centimeter wedge-shaped osteotomy at the level of the surgical neck to simulate medial calcar fracture comminution. Each pair of specimens had one arm randomly repaired with locking plate fixation, and the other arm repaired with locking plate fixation augmented with an intramedullary fibular autograft bone peg. The constructs were tested in bending to determine the failure loads, and initial stiffness using Digital Imaging Correlation (DIC) technology. The moment created by the rotator cuff was replicated by fixating the humeral head, and applying a point load to the distal humerus. A load was applied with a displacement rate of 4 mm/min, and was stopped approximately every 5 lbs to take a picture and record the load. This process was continued until failure of the specimens was obtained. Results: The intramedullary bone peg autograft increased the failure load of the constructs by 1.57±0.59 times (p = 0.026). Initial stiffness of the construct was also increased 3.13±2.10 times (p = 0.0079) with use of the bone peg. Conclusion: The stronger and stiffer construct provided by the addition of an intramedullary fibular allograft bone peg to locking plate fixation may help maintain reduction, and reduce the risk of fixation failure in surgical neck proximal humerus fractures with medial comminution.
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paper_title: In vivo glenohumeral contact forces--measurements in the first patient 7 months postoperatively.

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Knowledge of forces in the glenohumeral joint is essential for understanding normal and pathologic shoulder function. It forms the basis for performing fracture treatment or joint replacement surgery, for optimizing implant design and fixation and for improving and verifying analytical biomechanical models of the shoulder. An instrumented shoulder implant with telemetric data transmission was developed to measure six components of joint contact forces and moments. A patient with humeral head arthrosis achieved good joint function after its implantation. During the first 7 postoperative months, the contact force remained below 100% BW (percent body weight) for most activities of daily living. It ranged up to 130% BW for arm positions close to the limits of motion or when acting against external resistance. When the patient tried to turn a blocked steering wheel with maximum effort, the force rose to about 150% BW, the highest level observed thus far. Of great interest were the force directions relative to the humerus, especially those in the sagittal plane, which were not greatly influenced by the type of exercise, the arm position or the external resistance. The moments due to friction in the joint reached 5.2 Nm. The friction-induced shift of contact forces relative to the implant head centre ranged up to 6.3mm. These first worldwide in vivo measurements of glenohumeral contact forces are being continued in more patients and for longer postoperative times.
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paper_title: Biomechanics of four techniques for fixation of the four-part humeral head fracture

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OBJECTIVE ::: To carry out a biomechanical study of four techniques for fixation of four-part humeral head fractures. ::: ::: ::: METHODS ::: The fracture was reproduced in 40 plastic humeri, divided into groups of ten according to the fixation technique, each one employing different fixation resources, in different configurations. The humeral models were mounted on an aluminum scapula, with leather straps simulating the rotator cuff tendons, and submitted to bending and torsion tests in a universal testing machine, using relative stiffness as an evaluation parameter. Assemblies with intact humeri were analyzed for comparison. ::: ::: ::: RESULTS ::: The biomechanical behavior of the fixation techniques varied within a wide range, where the assemblies including the DCP plate and the 4.5mm diameter screws were significantly more rigid than the assemblies with the Kirschner wires and the 3.5mm diameter screws. ::: ::: ::: CONCLUSION ::: The four fixation techniques were able to bear loads compatible with the physiological demand, but those with higher relative stiffness should be preferred for clinical application. ::: ::: ::: LABORATORY INVESTIGATION ::: .
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paper_title: Biomechanical effect of the configuration of screw hole style on locking plate fixation in proximal humerus fracture with a simulated gap: A finite element analysis.

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BACKGROUND ::: Locking plate fixation for proximal humeral fractures is a commonly used device. Recently, plate breakages were continuously reported that the implants all have a mixture of holes allowing placement of both locking and non-locking screws (so-called combi plates). In commercialized proximal humeral plates, there still are two screw hole styles included "locking and dynamic holes separated" and "locking hole only" configurations. It is important to understand the biomechanical effect of different screw hole style on the stress distribution in bone plate. ::: ::: ::: METHODS ::: Finite element method was employed to conduct a computational investigation. Three proximal humeral plate models with different screw hole configurations were reconstructed depended upon an identical commercialized implant. A three-dimensional model of a humerus was created using process of thresholding based on the grayscale values of the CT scanning of an intact humerus. A "virtual" subcapital osteotomy was performed. Simulations were performed under an increasing axial load. The von Mises stresses around the screw holes of the plate shaft, the construct stiffness and the directional displacement within the fracture gap were calculated for comparison. ::: ::: ::: RESULTS ::: The mean value of the peak von Mises stresses around the screw holes in the plate shaft was the highest for combi hole design while it was smallest for the locking and dynamic holes separated design. The stiffness of the plate-bone construct was 15% higher in the locking screw only design (132.6N/mm) compared with the combi design (115.0N/mm), and it was 4% higher than the combi design for the locking and dynamic holes separated design (119.5N/mm). The displacement within the fracture gap was greatest in the combi hole design, whereas it was smallest for the locking hole only design. ::: ::: ::: CONCLUSIONS ::: The computed results provide a possible explanation for the breakages of combi plates revealed in clinical reports. The locking and dynamic holes separated design may be a better configuration to reduce the risk of plate fracture.
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paper_title: Magnitudes of local stress and strain along bony surfaces predict the course and type of fracture healing

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Abstract A new quantitative tissue differentiation theory which relates the local tissue formation in a fracture gap to the local stress and strain is presented. Our hypothesis proposes that the amounts of strain and hydrostatic pressure along existing calcified surfaces in the fracture callus determine the differentiation of the callus tissue. The study compares the local strains and stresses in the callus as calculated from a finite element model with histological findings from an animal fracture model. The hypothesis predicts intramembranous bone formation for strains smaller approximately ±5% and hydrostatic pressures smaller than ±0.15 MPa. Endochondral ossification is associated with compressive pressures larger than about −0.15 MPa and strains smaller than ±15%. All other conditions seemed to lead to connective tissue or fibrous cartilage. The hypothesis enables a better understanding of the complex tissue differentiation seen in histological images and the mechanical conditions for healing delayed healing or nonunions.
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paper_title: Biomechanical Contribution of Tension-Reducing Rotator Cuff Sutures in 3-Part Proximal Humerus Fractures.

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OBJECTIVES ::: Using a cadaveric 3-part fracture model and cyclic loading protocol, our study objectives were to quantify the stabilizing effect of tension-reducing rotator cuff sutures in terms of fracture displacement across the surgical neck and greater tuberosity compared with a control group in which no sutures were used. ::: ::: ::: METHODS ::: Six matched pairs of fresh frozen specimens underwent a standardized, 3-part, proximal humerus fracture and were split into 2 groups. The control group had the fracture fixed with a plate and screw construct only while the experimental group had additional suture fixation through the plate to each rotator cuff tendon. Active abduction through the rotator cuff was simulated for 100, 200, 300, and 400 cycles and to failure at 1000 N. A Mann-Whitney U test compared cyclic displacement of the greater tuberosity and surgical neck fracture gaps and load to failure between the 2 groups. ::: ::: ::: RESULTS ::: There was no significant difference (P > 0.05) in fracture gap between fixation methods at the surgical neck at 100 (P = 0.13), 200 (P = 0.07), 300 (P = 0.49), and 400 (P = 0.07) cycles. There was no significant difference (P > 0.05) between fixation methods in the fracture gap at the greater tuberosity at 100 (P = 0.39), 200 (P = 1.00), 300 (P = 0.31), and 400 (P = 0.59) cycles. There was no significant difference (P > 0.5) at 1000 N at the surgical neck (P = 0.70) or the greater tuberosity (P = 0.39). ::: ::: ::: CONCLUSIONS ::: Tension-relieving rotator cuff sutures do not add stability to the repair of 3-part proximal humerus fractures. Varus collapse and greater tuberosity displacement are common complications associated with 3-part fractures. No mechanical data exist to demonstrate benefit of adding suture to a plate and screw construct for limiting fracture displacement.
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paper_title: Biomechanical analysis of plate osteosynthesis systems for proximal humerus fractures.

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OBJECTIVES ::: To biomechanically assess five proximal, humeral, fracture-plate-fixation systems. ::: ::: ::: METHODS ::: Surgical neck fractures, with and without cortical contact, were created in 25 fresh-frozen cadaveric humeri. Five methods of plate fixation were used for repair: construct A [an eight-hole, low contact dynamic compression (LCDC) plate contoured into a blade shape, supported by one, 70-mm-long, 4.5-mm-diameter cortical screw acting as a truss], construct B (a 10-hole LCDC plate arrangement identical to construct A, but using one, 70-mm-long, 3.5-mm-diameter cortical screw as a truss), construct C [a five-hole dynamic compression (DC) blade plate with one, 6.5-mm-diameter cancellous screw], construct D (a five-hole T-plate supported by three, 6.5-mm-diameter cancellous screws), and construct E (a five-hole cloverleaf plate supported by five, 4-mm-diameter cancellous screws). Plates were posterior to the bicipital groove, 10 mm distal to the greater tuberosity tip, on the lateral aspect of the humeral shaft. Screw fixation was done using standard AO compression plating techniques. Stiffness of constructs was measured in bending and axial compression. Locked plates were not assessed. ::: ::: ::: RESULTS ::: For cortical contact [abduction of 20 degrees (P=0.02), flexion of 20 degrees (P=0.02), flexion of 90 degrees (P=0.005)] and no cortical contact [flexion of 90 degrees (P=0.0001)], construct A was significantly stiffer than other constructs. For no cortical contact in abduction of 90 degrees (P=0.05), construct A was significantly stiffer than other constructs. ::: ::: ::: CONCLUSIONS ::: Construct A was significantly stiffer than other constructs.
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paper_title: Retrograde nailing versus locking plate osteosynthesis of proximal humeral fractures: a biomechanical study

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Background In locking plate osteosynthesis of proximal humeral fractures, secondary varus malalignment is a specific complication. Retron nails (Tantum AG, Neumunster, Germany), among others, have been designed to improve medial support of the calcar humeri. The aim of our biomechanical study was to examine whether Retron nails provide increased stiffness for axial loads and adequate stiffness for torsional loads when compared with Philos plates (Synthes AG, Umkirch, Germany). Materials and methods Twenty-two fresh-frozen paired humeri were collected. After potting the specimens, intact bones were exposed to sinusoidal axial (10-120 N) and torsional (±2.5 Nm) loading for 8 cycles to calculate the initial stiffness and exclude pairs with differences. Afterward, an unstable proximal humeral fracture (AO 11-A3) was created by means of an oscillating saw, and the respective osteosynthesis devices were implanted. After another 4 cycles, initial changes in stiffness were measured. Subsequently, all specimens were tested for 1,000 cycles of loading before final stiffness was assessed. Results We found no statistically significant differences between Retron and Philos specimens after 4 or 1,000 cycles of loading. Conclusion Our study suggests that retrograde nailing provides sufficient stability for axial and torsional loading in 2-part fractures of proximal humeri.
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paper_title: Anatomical and biomechanical evaluation of an intramedullary nail for fractures of proximal humerus fractures based on tuberosity fixation.

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BACKGROUND ::: For unstable proximal humerus fractures, both plates and nails may be recommended. We introduce an anterograde nail designed for the treatment of 3- and 4-parts proximal humerus fractures. The aim of this study is to compare the biomechanics of this nail versus a plate and then to analyze the relationships of the screws with the axillary nerve. Our working hypotheses are as follows: (1) this nail is biomechanically equal or better to the reference plate and (2) it does not endanger the axillary nerve. ::: ::: ::: METHODS ::: Biomechanical study: using 40 sawbones, a reproducible 4-part fracture was created and fixed first with an angle-stable plate for proximal humeral fracture, then fixed with the nail using 2 posterior screws. All specimens were mounted in a custom testing apparatus. Two trails were performed needing each time 5 "normal" and 5 "osteoporotic" bones. ::: ::: ::: ANATOMICAL STUDY ::: On 20 unpaired shoulders, a nail was inserted with all screws through a superior approach (deltoid split approach). Dissection of all shoulders was done to identify the axillary nerve. The distance between each screw and the axillary nerve or its branches was measured. ::: ::: ::: FINDINGS ::: The proximal humerus nail demonstrated higher values than locking plate for both stiffness and load to failure. The failure mode differs in function of the type of osteosynthesis. The lowest distance between a screw and the axillary nerve was 20.13 mm. ::: ::: ::: INTERPRETATIONS ::: We introduce a biomechanically efficient nail without increased neurological risks to improve the pullout strength of the screws to provide more secure fixation of proximal humeral fractures. ::: ::: ::: LEVEL OF EVIDENCE ::: Basic Science Study, Anatomic Cadaver Study.
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paper_title: Correlations between mechanical stress history and tissue differentiation in initial fracture healing.

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A general theory for the role of intermittently imposed stresses in the differentiation of mesenchymal tissue is presented and then applied to the process of fracture healing. Two-dimensional finite element models of a healing osteotomy in a long bone were generated and the stress distributions were calculated throughout the early callus tissue under various loading conditions. These calculations were used in formulating theoretical predictions of tissue differentiation that were consistent with the biochemical and morphological observations of previous investigators. The results suggest that intermittent hydrostatic (dilatational) stresses may play an important role in influencing revascularization and tissue differentiation and determining the morphological patterns of initial fracture healing.
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paper_title: Can we trust ex vivo mechanical testing of fresh--frozen cadaveric specimens? The effect of postfreezing delays.

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BACKGROUND ::: Because embalming has been demonstrated to decrease the mechanical integrity of bone, most investigators favor fresh-frozen specimens for biomechanical evaluation. However, little is known about how the integrity of fresh--frozen specimens may change during biomechanical testing or may be affected by standard practices in testing. ::: ::: ::: OBJECTIVE ::: The purpose of this study was to evaluate how the time after removal from a freezer may affect the mechanical properties of fresh--frozen diaphyseal bone. ::: ::: ::: METHODS ::: Matched pairs of nonosteoporotic fresh--frozen human cadaveric femora were thawed before instrumentation with bicortical screws. Matched femora were reserved for either control or delayed use. Each specimen received standard diaphyseal bicortical screws (six or more in each group). At specified time points, screws were axially pulled out following the guidelines of ASTM F543-07. Test groups were stored in air (21 ± 0.5°C) for 16, 50, or 90 hours. In the control group, screws were pulled out at 16 hours, which corresponds to the minimum elapsed time for specimen thawing, instrumentation, potting, and biomechanical test initiation. This represents the baseline mechanical properties of the fresh--frozen bone at the inception of any biomechanical test. The 90-hour group corresponds to the time needed to cycle a construct 300,000 times at a physiological test frequency of 1 Hz. This corresponds approximately to 2 to 4 months of in vivo loading. A midpoint of 50 hours was also tested, representing approximately 180,000 cycles. ::: ::: ::: RESULTS ::: Failure for all specimens occurred as a result of bone failure at the screw-to-bone interface. There was a decrease in screw pullout strength as exposure time in air increased. The 50-hour test group showed a 9% decrease in screw pullout strength as compared with the 16-hour control group (P = 0.81). However, the 90-hour test group showed a 30% decrease in screw pullout strength as compared with the 16-hour control group (P = 0.04). ::: ::: ::: CONCLUSION ::: This study indicates that when using fresh-frozen cadaveric bone in biomechanical tests to simulate the orthopaedic clinical setting, specimen exposure time should be considered. The timing of testing should be kept constant between specimens to allow for a proper comparison. Furthermore, for fresh--frozen cadavers, the physical properties of bone may be detrimentally affected in biomechanical testing that exceeds the 50-hour time point after removal from the freezer.
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paper_title: Semitubular blade plate fixation in proximal humeral fractures: A biomechanical study in a cadaveric model

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This study was undertaken to compare the fixation of the semitubular blade plate with that of the AO T plate. Cadaveric humeri (n = 12 pairs) from an elderly population (41 to 89 years) had either a blade plate (n = 12) or a T plate (n = 12) fixed to them, subsequent to which a transverse osteotomy was performed. Mechanical testing in tension was performed in 1 series (n = 5, blade plate; n = 5, T plate) by applying a single maximal load to failure and in a second series (n = 7, blade plate; n = 7, T plate) by applying submaximal cyclic loading before failure was induced. Results showed that the fixation provided by the semitubular blade plate was significantly better (P <.05) than that of the T plate in those specimens subjected to submaximal cyclic loading before failure (series 2). This latter testing method contains some component of the clinical situation compared with monotonic distraction to failure. Based on these results plus favorable clinical results reported in the literature, the semitubular blade plate is possibly a better alternative to the T plate in the management of proximal humeral fractures that require open reduction and internal fixation. (J Shoulder Elbow Surg 1998;7:462-6.)
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paper_title: Biomechanical comparison of a unique locking plate versus a standard plate for internal fixation of proximal humerus fractures in a cadaveric model.

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BACKGROUND ::: Newer internal fixation devices with a locking mechanism between the plate and the screw have recently been released. The efficacy of these plates in the proximal humerus has yet to be fully described. There is a need to compare the biomechanical properties of efficacy of plate fixation with or without locking screws for surgery of two-part proximal humerus fractures. Multiple-plane locking plate and cloverleaf plate designs were tested to determine their ability to maintain fixation on the humeral head. ::: ::: ::: METHODS ::: Eight matched pairs of cadaveric shoulders with 7-millimeter osteotomy defects at the surgical neck simulating two-part fractures of the proximal humerus were loaded to failure in thirty degrees of glenohumeral abduction. One side was repaired with a proximal humerus locking plate and the other with a cloverleaf plate. The rotator cuff musculature was then loaded via a servo-hydraulic testing machine under displacement control to simulate the deforming forces present in vivo. ::: ::: ::: FINDINGS ::: The average maximum load to failure was greater in proximal humerus locking plates than in cloverleaf plates (876 versus 712; P=0.04). ::: ::: ::: INTERPRETATION ::: In the cadaveric, two-part proximal humerus fracture model that was created, the locking plate displayed significantly greater holding power of the humeral head. Clinical relevance is unproven but may be manifested in vivo as improved early range of motion exercises and functional outcome.
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paper_title: Timely Fracture-Healing Requires Optimization of Axial Fixation Stability

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BACKGROUND ::: Bone-healing is known to be sensitive to the mechanical stability of fixation. However, the influence on healing of the individual components of fixation stiffness remains unclear. The aim of this study was to investigate the relationship between the initial in vitro fixation stiffness and the strength and stiffness of the callus after nine weeks. We hypothesized that axial stiffness would determine the healing outcome. ::: ::: ::: METHODS ::: A standardized midshaft osteotomy of the right tibia was performed on Merino-mix sheep and was stabilized with either one of four monolateral external fixators or one of two tibial nails inserted without reaming. The in vitro stiffness of fixation was determined in six loading conditions (axial compression, torsion, as well as bending and shear in the anteroposterior and mediolateral planes) on ovine tibial specimens. Stiffness was calculated by relating displacements of the fracture fragments, determined by means of attached optical markers, and the loads applied by a materials testing machine. Torsional testing until failure of the explanted tibiae was performed with use of a standard materials testing machine after nine weeks of healing to determine the failure moment and the torsional stiffness of the healed tibia. ::: ::: ::: RESULTS ::: External fixation in sheep generally resulted in higher fixation stiffness than did conventional unreamed tibial nailing. The use of angle-stable locking screws in tibial nailing resulted in fixation stiffness comparable with that of external fixation. The highest torsional moment to failure was observed for the external fixator with moderate axial stiffness and high shear stiffness. The fixator with the highest axial stability did not result in the highest failure moment. Low axial stability in combination with low shear stability resulted in the lowest failure moment. ::: ::: ::: CONCLUSIONS ::: In this study, a clear relationship between the stability of fixation and the mechanical strength of the healing tibia was seen. Moderate levels of axial stability were associated with the highest callus strength and stiffness.
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paper_title: Application of Additional Medial Plate in Treatment of Proximal Humeral Fractures With Unstable Medial Column: A Finite Element Study and Clinical Practice

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AbstractThe purpose of this study was to use finite element analysis to compare the biomechanical characteristics after lateral locking plate (LLP) or LLP with a medial anatomical locking plate (LLP-MLP) fixation of proximal humeral fractures with an unstable medial column.First, a 3-dimensional, finite element analysis model was developed. Next, LLP and LLP-MLP implants were instrumented into the proximal humeral fracture models. Compressive and rotational loads were then applied to the humerus model to determine the biomechanical characteristics. Both normal and osteoporotic proximal humerus fractures were simulated using 2 internal fixation methods each under 7 loading conditions. To assess the biomechanical characteristics, the construct stiffness, fracture micromotion, and stress distribution on the implants were recorded and compared.The LLP-MLP method provided both lateral and medial support that reduced the stress on the LLP and the amount of displacement in the fracture region. In contrast, the LLP method resulted in more instability in the medial column and larger magnitudes of stress. In osteoporotic bone, the LLP was more inclined to fail than LLP-MLP.The LLP-MLP method provides a strong support for the medial column and increases the stability of the region surrounding the fracture.
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paper_title: Proximal Humeral Fractures: A Biomechanical Comparison of Locking Plate Constructs in a Cadaveric 3-Part Fracture Model

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The purpose of our study was to biomechanically compare, under cyclic loading conditions, fracture site motion, humeral head collapse, and intra-articular hardware penetration in simulated 3-part osteoporotic proximal humeral fractures stabilized with 1 of 2 locking-plate constructs. We performed fixation on simulated 3-part proximal humeral fractures in 10 pairs of cadaveric osteoporotic humeri with a Hand Innovations S3 Proximal Humerus Plate (S3 plate) or an LCP Proximal Humerus Plate (LCP plate; 1 each for each pair). The specimens were potted, mounted on a materials testing machine, and subjected to 5000 cycles of abduction in the scapular plane, loading through the supraspinatus tendon. Interfragmentary displacement at 2 virtual points (the most medial aspect of the calcar and the most superior aspect of the osteotomy line between the greater tuberosity and humeral head) was measured using an optical tracking system. Humeral head rotation was also measured. We used a generalized linear latent and mixed model to check for an effect of cyclic loading and treatment on the parameters of interest (significance, P < .05). After cyclic loading, the S3 plate humeri showed significantly greater displacement of the greater tuberosity fragment and rotation of the humeral head and a trend (not a significant difference) toward greater displacement at the calcar. No hardware penetration was noted for either repair. Although the S3 plate repairs resulted in significantly more fracture site motion, it is unknown whether the magnitude of the motion is clinically significant.
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paper_title: Medial support by fibula bone graft in angular stable plate fixation of proximal humeral fractures: an in vitro study with synthetic bone.

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BACKGROUND ::: Failure to achieve stable fixation with medial support in proximal humeral fractures can result in varus malalignment and cut-through of the proximal screws. The purpose of this study was to investigate the influence of an intramedullary fibula bone graft on the biomechanical properties of proximal humeral fractures stabilized by angular stable plate fixation in a bone model under cyclic loading. ::: ::: ::: METHODS ::: Two fixation techniques were tested in 20 composite analog humeri models. In group F- (n = 10), fractures were fixed by an anatomically formed locking plate system. In group F+ (n = 10), the same fixation system was used with an additional fibular graft model with a length of 6 cm inserted in an intramedullary manner. Active abduction was simulated for 400 cycles by use of a recently established testing setup. Fragment gap distance was measured, and thereby, intercyclic motion, fragment migration, and residual plastic deformation were determined. ::: ::: ::: RESULTS ::: The addition of a fibular graft to the fixation plate led to 5 times lower intercyclic motion, 2 times lower fragment migration, and 2 times less residual plastic deformation. Neither screw pullout, cut-through, nor implant failure was observed. ::: ::: ::: CONCLUSION ::: Medial support with an intramedullary fibular graft in an angular stable fixation of the proximal humerus in vitro increases overall stiffness of the bone-implant construct and reduces migration of the humeral head fragment. This technique might provide a useful tool in the treatment of displaced proximal humeral fractures, especially when there is medial comminution.
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paper_title: Telemetering in vivo loads from nail plate implants.

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A system of multi-channel telemetry capable of broadcasting in vivo loading from orthopaedic implants is presented. Its use to monitor the two orthogonal bending moments about the nail plate junction of three implanted hip nails is described. Typical results from these cases in which the telemeterized implant was employed to treat proximal femoral fixation and osteotomy are given.
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paper_title: Technical tips: dualplate fixation technique for comminuted proximal humerus fractures.

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Abstract The authors report dualplate fixation technique for providing stable fixation in comminuted proximal humerus fractures. This technique has been used for proximal humerus fractures with metaphyseal comminution and provides excellent anatomical reduction and neck shaft angle (NSA). The recently locking plate is clinically more widely used due to its small size, low rigidity, high elasticity, and biomechanical properties such as fixed initial angle and rotational stability. However, in severely comminuted complex type proximal metaphyseal humerus fractures, the use of locking plate alone does not provide stable fixation, leading to complications such as varus collapse, anterior–posterior angulation, screw cutout, nonunion, malunion, and metal failure. Therefore, a more robust and enhanced fixation method, the dual plating technique using the locking compression plate (Proximal Humeral Internal Locking System and Variable Angle Locking Compression Plate) was developed.
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paper_title: In vivo measurement of shoulder joint loads during activities of daily living.

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Until recently the contact loads acting in the glenohumeral joint have been calculated using musculoskeletal models or measured in vitro. Now, contact forces and moments are measured in vivo using telemeterized shoulder implants. Mean total contact forces from four patients during eight activities of daily living are reported here. Lifting a coffee pot (1.5kg) with straight arm caused an average force of 105.0%BW (%body weight) (range: 90-124.6%BW), while setting down the coffee pot in the same position led to higher forces of 122.9%BW on the average (105.3-153.4%BW). The highest joint contact forces were measured when the straight arm was abducted or elevated by 90 degrees or more, with a weight in the hand. Lifting up 2kg from a board up to head height caused a contact force of 98.3%BW (93-103.6%BW); again, setting it down on the board led to higher forces of 131.5%BW (118.8-144.1%BW). In contrast to previously calculated high loads, the contact force during passive holding of a 10kg weight laterally was only 12.3%BW (9.2-17.9%BW), but when lifting it up to belt height it increased to 91.5%BW (87-95%BW). The moments transferred inside the joint at our patients varied much more than did the forces both inter and intra-individually. Our data suggest that patients with shoulder problems or during the first post-operative weeks after shoulder fractures or joint replacements should avoid certain activities encountered during daily living e.g. lifting or holding a weight with an outstretched arm. Some energy-related optimization criteria used in the literature for analytical musculoskeletal shoulder models must now be reconsidered.
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paper_title: Biomechanical testing of the LCP--how can stability in locked internal fixators be controlled?

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New plating techniques, such as non-contact plates, have been introduced in acknowledgment of the importance of biological factors in internal fixation. Knowledge of the fixation stability provided by these new plates is very limited and clarification is still necessary to determine how the mechanical stability, e.g. fracture motion, and the risk of implant failure can best be controlled. The results of a study based on in vitro experiments with composite bone cylinders and finite element analysis using the Locking Compression Plate (LCP) for diaphyseal fractures are presented and recommendations for clinical practice are given. Several factors were shown to influence stability both in compression and torsion. Axial stiffness and torsional rigidity was mainly influenced by the working length, e.g. the distance of the first screw to the fracture site. By omitting one screw hole on either side of the fracture, the construct became almost twice as flexible in both compression and torsion. The number of screws also significantly affected the stability, however, more than three screws per fragment did little to increase axial stiffness; nor did four screws increase torsional rigidity. The position of the third screw in the fragment significantly affected axial stiffness, but not torsional rigidity. The closer an additional screw is positioned towards the fracture gap, the stiffer the construct becomes under compression. The rigidity under torsional load was determined by the number of screws only. Another factor affecting construct stability was the distance of the plate to the bone. Increasing this distance resulted in decreased construct stability. Finally, a shorter plate with an equal number of screws caused a reduction in axial stiffness but not in torsional rigidity. Static compression tests showed that increasing the working length, e.g. omitting the screws immediately adjacent to the fracture on both sides, significantly diminished the load causing plastic deformation of the plate. If bone contact was not present at the fracture site due to comminution, a greater working length also led to earlier failure in dynamic loading tests. For simple fractures with a small fracture gap and bone contact under dynamic load, the number of cycles until failure was greater than one million for all tested constructs. Plate failures invariably occurred through the DCP hole where the highest von Mises stresses were found in the finite element analysis (FEA). This stress was reduced in constructions with bone contact by increasing the bridging length. On the other hand, additional screws increased the implant stress since higher loads were needed to achieve bone contact. Based on the present results, the following clinical recommendations can be made for the locked internal fixator in bridging technique as part of a minimally invasive percutaneous osteosynthesis (MIPO): for fractures of the lower extremity, two or three screws on either side of the fracture should be sufficient. For fractures of the humerus or forearm, three to four screws on either side should be used as rotational forces predominate in these bones. In simple fractures with a small interfragmentary gap, one or two holes should be omitted on each side of the fracture to initiate spontaneous fracture healing, including the generation of callus formations. In fractures with a large fracture gap such as comminuted fractures, we advise placement of the innermost screws as close as practicable to the fracture. Furthermore, the distance between the plate and the bone ought to be kept small and long plates should be used to provide sufficient axial stiffness.
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paper_title: Forces at the Glenohumeral Joint in Abduction

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The purpose of this study was to determine the forces in the glenohumeral joint for isometric abduction (including all directions of rotation) in the plane of the scapula. The lines of actions of muscles were obtained from 3 upper quarter specimens, electromyographic data was used, as well as geometrical parameters of shoulder motion. The main assumption made in the analysis was that the force in a muscle was proportional to its area times the integrated electromyographic signal. The resultant force reached a maximum of 0.89 times body weight at 90 degrees of abduction, while the shearing component up the face of the glenoid was a maximum of 0.42 times body weight at 60 degrees of abduction.
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paper_title: Proximal humeral fractures: what is semi-rigid? Biomechanical properties of semi-rigid implants, a biomechanical cadaver based evaluation

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INTRODUCTION ::: Proximal humerus fractures remain challenging especially in the elderly. Biomechanical data put semi-rigid implants in favour of osteopenic or osteoporotic situation. Little surgical side damage is associated with a minimal invasive approach of these implants. The aim of this study was to evaluate the mechanical properties of three such implants. ::: ::: ::: MATERIAL AND METHODS ::: Fresh frozen cadaver specimens were mounted as proposed by the distributors. Three different implants were used: LCP-PH (locking compression plate proximal humerus, Synthes, Austria), HB (humerus block, Synthes, Austria), and IMC (intramedullary claw, ITS, Austria). Subcapital fracture was simulated by resecting a 5 mm gap. All specimens were comparable in "B" (one), "M" (ineral) and "D" (ensity). Four load cases were tested: varus bending, medial shearing and axial torque. A cyclic test (1,000 cycles) was performed in the first load case (varus stress) for all three implants. ::: ::: ::: RESULTS ::: The LCP-PH was the most rigid in all three load cases, always followed by the HB. The IMC was the most elastic device with almost immeasurable values in axial torque. In the cyclic setting, the load reduction of the HB followed by the LCP-PH was significantly better than that for the IMC. ::: ::: ::: CONCLUSION ::: The differences in stiffness are varying tremendously. The IMC is the implant with the lowest stiffness in all load cases and the highest load reduction. New "semi-rigids" claim good clinical performance, yet prospective clinical studies have to prove this. It is unlikely that the IMC can maintain fracture reduction in fracture situations of complex nature (no ligamentotaxis).
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paper_title: In vivo gleno-humeral joint loads during forward flexion and abduction.

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To improve design and preclinical test scenarios of shoulder joint implants as well as computer-based musculoskeletal models, a precise knowledge of realistic loads acting in vivo is necessary. Such data are also helpful to optimize physiotherapy after joint replacement and fractures. This is the first study that presents forces and moments measured in vivo in the gleno-humeral joint of 6 patients during forward flexion and abduction of the straight arm. The peak forces and, even more, the maximum moments varied inter-individually to a considerable extent. Forces of up to 238%BW (percent of body weight) and moments up to 1.74%BWm were determined. For elevation angles of less than 90° the forces agreed with many previous model-based calculations. At higher elevation angles, however, the measured loads still rose in contrast to the analytical results. When the exercises were performed at a higher speed, the peak forces decreased. The force directions relative to the humerus remained quite constant throughout the whole motion. Large moments in the joint indicate that friction in shoulder implants is high if the glenoid is not replaced. A friction coefficient of 0.1–0.2 seems to be realistic in these cases.
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paper_title: Three-dimensional analysis of the proximal part of the humerus: relevance to arthroplasty.

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BACKGROUND ::: Recreation of normal anatomical relationships may be important to optimize the outcome of proximal humeral arthroplasty. With use of computerized tomographic data and three-dimensional computer modeling, we concurrently studied both extramedullary and intramedullary humeral morphology, including canal shape, and related these findings to the design of proximal humeral prostheses. ::: ::: ::: METHODS ::: Sixty cadaveric humeri (thirty pairs: fifteen from male donors and fifteen from female donors) were studied. Three-dimensional computer models were built from canal and periosteal contours extracted from computerized tomographic data and multiple measured anatomical parameters, including humeral canal axis, humeral head center, and hinge point offset; greater tuberosity and bicipital groove offset; humeral head center, radius, thickness, retroversion, and inclination; and size and torsion of sections of the canal. ::: ::: ::: RESULTS ::: On the average, the humeral head center was offset both medially (seven millimeters) and posteriorly (two millimeters) from the humeral axis. The humeral head hinge point did not line up with the axis but instead was laterally offset by an average of seven millimeters. The average humeral head thickness was nineteen millimeters. The humeral head thickness and length were proportionately linked. There was marked variability in all of these parameters. Humeral head inclination averaged 41 degrees but was less variable than previously described, with 95 percent of our sample within the range of 35 to 46 degrees. The proximal section of the humeral canal was retroverted, and the retroversion was found to be similar to that of the humeral head on statistical analysis. Version of the middle and distal sections of the canal, however, was dissimilar to that of the proximal section of the canal. Proximal humeral retroversion was found to be extremely variable and averaged 19 degrees. The accuracy, reliability, and repeatability of the computer-based-model measurements were found to be excellent. ::: ::: ::: CONCLUSIONS ::: Measurements of external proximal humeral morphology made with three-dimensional computer models of cadaveric specimens derived from the Midwestern United States agreed, in general, with those described for different populations evaluated with different measuring techniques. Proximal humeral morphology was extremely variable as highlighted by the large ranges of measurements seen for all variables. Examination of the intramedullary morphology showed that there is an internal version, with measurements dependent on the canal distance distal to the anatomical neck. ::: ::: ::: CLINICAL RELEVANCE ::: Because of the marked variabilities seen in proximal humeral morphology, newer prosthetic designs are now allowing surgeons to control multiple prosthetic variables. An understanding of the normal values for proximal humeral morphology can serve as an important guideline for component selection, especially when the normal anatomy is distorted. Additionally, variations in intramedullary version may have important consequences for future designs of press-fit proximal humeral replacement.
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paper_title: Clinical and radiological outcomes of unstable proximal humeral fractures treated with a locking plate and fibular strut allograft

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PURPOSE ::: To evaluate the clinical and radiological outcomes of unstable proximal humeral fractures (PHFs) treated with a locking plate and fibular strut allograft. ::: ::: ::: METHODS ::: This study included 36 patients [7 men, 29 women; mean age, 68 years (range, 22-94 years)] with unstable PHFs with medial column disruption. All patients were treated with open reduction and internal fixation using a locking plate and fibular strut allograft. Post-operative assessment included clinical outcomes, shoulder range of motion, radiographic examination, and any complications. Post-operative radiological assessment including the humerus neck-shaft angle (NSA) and the humeral head height was performed. ::: ::: ::: RESULTS ::: At the mean two year follow-up visit, the mean American Shoulder and Elbow Society (ASES) and University of California, Los Angeles (UCLA) scores were 77 and 28, respectively. According to the UCLA rating scale, the result was excellent in six, good in 20, fair in six, and poor in four cases. According to the Paavolainen method, 31 patients had good results with an NSA of 130 ± 10°; three patients showed fair results with an NSA of 100-120°, and two patients experienced a poor result with an NSA of <100°. When calculating the humeral head height, the mean loss of reduction was measured as 1.6 mm (from 10.8 or 9.2 mm). Varus collapse and avascular necrosis of the humeral head was noted in two patients for each condition. ::: ::: ::: CONCLUSIONS ::: For unstable proximal humerus fractures, particularly in elderly patients with severe osteoporosis or in younger patients with a four-part fracture, locking plate fixation with a fibular strut allograft provided rigid medial support and showed satisfactory clinical and radiological outcomes.
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paper_title: Surgical neck fractures of the proximal humerus : a laboratory evaluation of ten fixation techniques

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Objective : A biomechanical cadaver study was performed to compare the stability and ultimate strength of ten standard fixation techniques used for the treatment of surgical neck fractures of the proximal humerus. Design : One hundred twenty (60 fresh frozen, 60 embalmed) proximal humerus specimens were selected and divided into two groups : fresh frozen specimens represented a nonosteopenic group and embalmed specimens an osteopenic group. Simulated fractures were created at the level of the surgical neck, reduced, and randomly assigned to one of ten methods of fixation (six fresh frozen and six embalmed specimens per fixation group). These constructs were then mechanically tested with the humeri oriented to create primarily shear loading of the fixation. Results and Conclusions : The T-plate and screws provided significantly stronger fixation (p < 0.005) in the fresh frozen specimens than all other methods. The Ender nails/tension band construct was the second strongest fixation technique, providing significantly stronger fixation (p < 0.01) than all the remaining techniques. Four Schanz pins with one pin placed through the greater tuberosity followed by the T-plate and screws provided the strongest fixation in embalmed specimens. Tension band fixation in both humeral groups was shown to provide the least effective fixation.
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paper_title: Biomechanical in vitro assessment of fixed angle plating using a new concept of locking for the treatment of osteoporotic proximal humerus fractures

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Locked plating attempts to improve mechanical stability via better anchorage of the screws in the bone. In 22 paired osteoporotic humeri an AO/ASIF 11-B 1 fracture was created. Locked and conventional plating using the same device of the latest generation was performed. Torsional loading around three axes (x = varus/valgus, y = flexion/extension, z = axial rotation) with an increasing moment (2, 3.5, 5 and 7.5 N·m) was applied. Interfragmentary motion within the locked group was lower for all three axes with higher cumulative survival rates (p < 0.05). The typical mode of failure was loss of fixation in the humeral head occurring earlier in the conventional group. The locking mechanism investigated provides more ultimate strength in an osteoporotic proximal humerus fracture model. Correlation with BMD suggests that this device may especially be suitable for use in osteoporotic bone.
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paper_title: Biomechanical comparison of a proximal humeral locking plate using two methods of head fixation.

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HYPOTHESIS ::: Locking plates have emerged as the implant of choice for stabilization of proximal humeral fractures. The biomechanical properties of a locked plating system using smooth pegs vs threaded screws for fixation of the humeral head were compared to test the hypothesis that there would be no biomechanical difference between pegs and threaded screws. ::: ::: ::: MATERIALS AND METHODS ::: Sixteen pairs of fresh frozen cadaveric humeri were randomized to have a surgical neck gap osteotomy stabilized with a locked plate using threaded screws (n=8) or smooth pegs (n=8). The intact contralateral humerus served as a control. Each specimen was tested with simultaneous cyclic axial compression (40 Nm) and torsion (both +/-2 Nm and +/-5 Nm) for 6000 cycles. All specimens were loaded to failure. Interfragmentary motion and load-displacement curves were analyzed to identify differences between the groups. Our data were then compared to previously published forces across the glenohumeral joint to provide evidence based recommendations for postoperative use of the shoulder. ::: ::: ::: RESULTS ::: There was a statistically significant difference between test specimens and their paired control (P < .001) in cyclic testing and load to failure. Differences between the smooth pegs and threaded screws were not statistically significant. ::: ::: ::: DISCUSSION ::: There is no biomechanical difference between locked smooth pegs and locked threaded screws for proximal fragment fixation in an unstable 2-part proximal humeral fracture model. ::: ::: ::: CONCLUSION ::: Our study contributes to the published evidence evaluating forces across the glenohumeral joint and suggests that early use of the affected extremity for simple activities of daily living may be safe. Use of the arm for assisted ambulation requiring a crutch, cane, walker, or wheelchair should be determined on a case-by-case basis.
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paper_title: Influence of plate material and screw design on stiffness and ultimate load of locked plating in osteoporotic proximal humeral fractures

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Abstract Introduction The main purpose was to compare the biomechanical properties of a carbon-fibre reinforced polyetheretherketone (CF-PEEK) composite locking plate with pre-existing data of a titanium-alloy plate when used for fixation of an unstable 2-part fracture of the surgical neck of the humerus. The secondary purpose was to compare the mechanical behaviour of locking bolts and conventional locking cancellous screws. Methods 7 pairs of fresh frozen human humeri were allocated to two equal groups. All specimens were fixed with the CF-PEEK plate. Cancellous screws (PEEK/screw) were compared to locking bolts (PEEK/bolt) for humeral head fixation. Stiffness, fracture gap deflection and ultimate load as well as load before screw perforation of the articular surface were assessed. Results were compared between groups and with pre-existing biomechanical data of a titanium-alloy plate. Results The CF-PEEK plate featured significantly lower stiffness compared to the titanium-alloy plate ( P P > 0.05). Discussion The CF-PEEK plate has more elastic properties and significantly increases movement at the fracture site of an unstable proximal humeral fracture model compared to the commonly used titanium-alloy plate. The screw design however does neither affect the constructs primary mechanical behaviour in the constellation tested nor the load before screw perforation.
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paper_title: Biomechanical comparison of an angular stable plate with augmented and non-augmented screws in a newly developed shoulder test bench.

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BACKGROUND ::: The proximal humeral fracture is one of the most common fractures. Although there are a number of treatment options available, the clinical outcomes in geriatric patients are still unsatisfactory. Therefore, the aim of this study was to investigate the biomechanical behaviour of an angular stable plate with either augmented or non-augmented screws using two different fracture models in a shoulder test bench with active muscle forces. ::: ::: ::: METHODS ::: Six paired fresh-frozen humeri were loaded into a shoulder test bench simulating ab- and adduction between 15 and 45° induced by active muscle forces. The bone mineral density was measured by a quantitative CT. A two-part fracture model (stable and an unstable) was used to investigate the different biomechanical behaviours of the PHILOS plate, either utilising cannulated screws, allowing in situ augmentation, or without utilising augmented screws. Four screws were augmented with 0.5ml PMMA cement. ::: ::: ::: FINDINGS ::: The in vitro-measured resulting forces in the glenoid fossa were comparable to the in vivo forces generated in shoulder arthroplasties. Under stable conditions, the per cycle motion and varus impaction tilting showed no significant difference. In the unstable state, the augmented group showed a maximum of 0.81° per cycle motion and a maximum varus impaction of -1.46° compared to the non-augmented maximum of 2.31° per cycle motion and maximum varus impaction of -4.26° (P<0.05). ::: ::: ::: INTERPRETATION ::: In an unstable fracture model under dynamic testing conditions, augmentation leads to a decreased per cycle motion and varus impaction of the humeral head.
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paper_title: BIOMECHANICAL EVALUATION OF PROXIMAL HUMERAL FRACTURE FIXATION SUPPLEMENTED WITH CALCIUM PHOSPHATE CEMENT

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Background: Proximal humeral fractures are common injuries, and numerous surgical methods have been described for their treatment. The biomechanical characteristics of various internal fixation devices that are used to treat these fractures have not been extensively studied, nor has the potential beneficial effect of calcium phosphate cement supplementation. Methods: We used a cadaveric three-part proximal humeral osteotomy model to perform a biomechanical evaluation of three types of internal fixation devices: a cloverleaf plate, an angled blade-plate, and Kirschner wires. The effect of supplementing the fixation with SRS (Skeletal Repair System) calcium phosphate cement was evaluated as well. Eighteen pairs of fresh-frozen humeri were obtained, and the bone-mineral density of each specimen was measured. In each pair, one specimen was secured with internal fixation alone and the contralateral specimen was secured with internal fixation combined with calcium phosphate cement. The specimens were tested cyclically in abduction and in external rotation for 250 cycles to evaluate interfragmentary motion. The specimens were then loaded to failure in external rotation to measure torsional load to failure and torsional stiffness. Results: Overall, there were no significant differences between the specimens treated with the blade and cloverleaf plates, whereas the specimens treated with Kirschner wires demonstrated more interfragmentary motion, less stiffness, and lower torque to failure. In general, supplementation with calcium phosphate cement led to significant improvements in the mechanical performance of all three forms of internal fixation as demonstrated by a significant decrease in interfragmentary motion, a significant increase in torque to failure, and a significant increase in torsional stiffness. The addition of calcium phosphate cement increased the stiffness of even the most osteoporotic specimens to levels that were higher than those of the most osteodense specimens that had been treated with internal fixation alone. Conclusion: The initial biomechanical properties of internal fixation as measured with use of a proximal humeral osteotomy model and three methods of fixation were significantly improved by the addition of calcium phosphate cement. Clinical Relevance: The addition of calcium phosphate cement may augment the mechanical characteristics of internal fixation of difficult, three-part proximal humeral fractures. The ability to stabilize the interface between the implant and cancellous bone, particularly in the presence of osteopenia, may make calcium phosphate cement a valuable clinical tool in the treatment of these difficult fractures.
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paper_title: Impact of shoulder rotation on neck-shaft angle: A clinical study☆

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Abstract Background Two recent experimental studies evaluated the influence of shoulder rotation on neck-shaft angle, with conflicting results. However, there have been no clinical studies of whether this angle varies in different shoulder positions. The present study aimed to determine whether shoulder rotation affects neck-shaft angle on standard radiographs in patients with complaints of shoulder pain. Hypothesis Shoulder rotation does not affect neck-shaft angle. Materials and methods A prospective study was conducted in selected patients with shoulder pain. Three true anterior-posterior radiographic views were obtained: in neutral rotation, 30° external rotation, and internal rotation with patient's arm in a sling. The X-rays were evaluated by three shoulder and elbow surgeons. Inter- and intra-observer reliability was evaluated by intraclass correlation coefficient (ICC). Results Neck-shaft angle on true AP view did not differ between neutral rotation and 30° external rotation: 132 ± 6° and 130 ± 9°, respectively ( P > 0.999). In internal rotation with the hand resting on the abdomen, neck-shaft angle was 145 ± 6°: i.e., significantly different ( P Conclusions Radiographic neck-shaft angle was significantly different in internal rotation with the patient's arm in a sling, compared with views in neutral or 30° external rotation. Intra- and inter-observer correlation showed excellent reliability. Level of evidence II, comparative prospective study.
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paper_title: Biophysical stimuli on cells during tissue differentiation at implant interfaces

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Abstract If musculoskeletal tissues are indeed efficient for their mechanical function, it is most reasonable to assume that this is achieved because the mechanical environment in the tissue influences cell differentiation and expression. Although mechanical stimuli can influence the transport of bioactive factors, cell deformation and cytoskeletal strain, the question of whether or not they have the potential to regulate tissue differentiation sequences (for example, during fracture healing or embryogenesis) has not been answered. To assess the feasibility of biophysical stimuli as mediators of tissue differentiation, we analysed interfacial tissue formation adjacent to a micromotion device implanted into the condyles of dogs. A biphasic finite element model was used and the mechanical environment in the tissue was characterised in terms of (i) forces opposing implant motion, (ii) relative velocity between constituents, (iii) fluid pressure, (iv) deformation of the tissue and (v) strain in the tissue. It was predicted that, as tissue differentiation progressed, subtle but systematic mechanical changes occur on cells in the interfacial tissue. Specifically, as the forces opposing motion increase, the implant changes from being controlled by the maximum-allowable displacement (motion-control) to being controlled by the maximum-available load (force-control). This causes a decrease in the velocity of the fluid phase relative to the solid phase and a drop in interstitial fluid pressure accompanied by a reduction in peri-prosthetic tissue strains. The variation of biophysical stimuli within the tissue can be plotted as ‘mechano-regulatory pathway’, which identifies the transition from motion-control to force-control as a branching event in the tissue differentiation sequence.
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paper_title: PEEK versus titanium locking plates for proximal humerus fracture fixation: a comparative biomechanical study in two- and three-part fractures

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Introduction ::: The high rigidity of metal implants may be a cause of failure after fixation of proximal humerus fractures. Carbon fiber-reinforced polyetheretherketone (PEEK) plates with a modulus similar to human cortical bone may help to overcome this problem. The present study assesses the biomechanical behavior of a PEEK plate compared with a titanium locking plate.
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paper_title: Mechanobiology of skeletal regeneration

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Skeletal regeneration is accomplished by a cascade of biologic processes that may include differentiation of pluripotential tissue, endochondral ossification, and bone remodeling. It has been shown that all these processes are influenced strongly by the local tissue mechanical loading history. This article reviews some of the mechanobiologic principles that are thought to guide the differentiation of mesenchymal tissue into bone, cartilage, or fibrous tissue during the initial phase of regeneration. Cyclic motion and the associated shear stresses cause cell proliferation and the production of a large callus in the early phases of fracture healing. For intermittently imposed loading in the regenerating tissue : (1) direct intramembranous bone formation is permitted in areas of low stress and strain; (2) low to moderate magnitudes of tensile strain and hydrostatic tensile stress may stimulate intramembranous ossification; (3) poor vascularity can promote chondrogenesis in an otherwise osteogenic environment; (4) hydrostatic compressive stress is a stimulus for chondrogenesis; (5) high tensile strain is a stimulus for the net production of fibrous tissue; and (6) tensile strain with a superimposed hydrostatic compressive stress will stimulate the development of fibrocartilage. Finite element models are used to show that the patterns of tissue differentiation observed in fracture healing and distraction osteogenesis can be predicted from these fundamental mechanobiologic concepts. In areas of cartilage formation, subsequent endochondral ossification normally will proceed, but it can be inhibited by intermittent hydrostatic compressive stress and accelerated by octahedral shear stress (or strain). Later, bone remodeling at these sites can be expected to follow the same mechanobiologic adaptation rules as normal bone.
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paper_title: The Humerusblock NG: a new concept for stabilization of proximal humeral fractures and its biomechanical evaluation

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Background ::: The Humerusblock NG represents a new semi-rigid angular stable fixation device for minimally invasive stabilization of proximal humeral fractures. This study evaluates the function and stability of the Humerusblock NG and its biomechanical properties on the basis of two different fracture models under cyclic loading.
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paper_title: No Contribution of Tension-Reducing Rotator Cuff Sutures on Locking Plate Fixation in a 2-Part Proximal Humerus Fracture Model.

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OBJECTIVES ::: Varus failure is a well-known complication of open reduction internal fixation of proximal humeral fractures. The addition of tension-reducing sutures from the plate to the rotator cuff may attenuate the deforming forces of the rotator cuff resulting in decreased varus failure. In this study, we investigate the biomechanical contributions of tension-reducing sutures to a locked plate construct in a 2-part proximal humerus fracture model. ::: ::: ::: METHODS ::: Two fixation techniques were tested in 12 matched fresh frozen humeri in which standard 2-part fractures of the surgical neck were created with a gap simulating surgical neck medial comminution. In group 1, fractures were fixed with a standard proximal humerus locking plate. In group 2, the plate fixation was similar, and additionally, tension-reducing sutures were applied from the plate to the rotator cuff. Active abduction was simulated for 400 cycles with force applied through the rotator cuff tendons. Intercyclic fracture motion, change in displacement, and load to failure were recorded. ::: ::: ::: RESULTS ::: The addition of tension-reducing sutures did not lead to significant differences in intercyclic fracture motion. The mean change in displacement and load to failure were similar in both groups. Failure typically occurred in both groups at the rotator cuff testing clamp interface. ::: ::: ::: CONCLUSIONS ::: Tension-relieving rotator cuff sutures added to locking plate fixation did not lead to a change in fracture gap with cyclic loading or an increase in ultimate failure load in a 2-part surgical neck proximal humerus fracture model without medial support.
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paper_title: The Mechanical Benefit of Medial Support Screws in Locking Plating of Proximal Humerus Fractures

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Background ::: The purpose of this study was to evaluate the biomechanical advantages of medial support screws (MSSs) in the locking proximal humeral plate for treating proximal humerus fractures.
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paper_title: Biomechanical effects of calcar screws and bone block augmentation on medial support in locked plating of proximal humeral fractures

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Abstract Background The objective of this study was to investigate the biomechanical effects of medial fracture gap augmentation in locked plating of an unstable 2-part proximal humeral fracture with calcar screws and insertion of a corticocancellous bone block. Furthermore the mechanical behavior of dynamic locking screws in the non-parallel arrangement of a proximal humeral plate was of interest. Methods Thirty-two fresh frozen humeri were randomized in four equal groups. An unstable 2-part fracture was fixed by locked plating in all specimens. The basic screw setup was supplemented by additional calcar screws in one group. Humeral head screws were replaced by dynamic locking screws in a second group. The third group featured an additional corticocancellous femoral head allograft. Assessment of stiffness was followed by cyclic loading and load to failure tests. Resulting stiffness, fracture gap deflection and ultimate load were compared utilizing Bonferroni corrected t-test for independent samples. Findings The mechanical effect of additional calcar screws was non-significant as compared to the basic screw configuration whereas bone block insertion significantly increased construct stiffness and failure load. The use of dynamic locking screws did not significantly reduce construct stiffness when compared to conventional locking screws. Interpretation Additional calcar screws alone did not improve the initial biomechanical properties of an unstable 2-part proximal humeral fracture model. However bone block augmentation appeared to be a reliable alternative of additional bony support by raising stiffness and failure load. Dynamic locking screws did not show their expected dynamic component when used in a non-parallel arrangement.
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paper_title: 45. BIOMECHANICAL ANALYSIS OF PROXIMAL HUMERAL FIXATION USING LOCKING PLATE FIXATION WITH AN INTRAMEDULLARY FIBULAR ALLOGRAFT

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Purpose: The purpose of this study is to compare two fixation methods for surgical neck proximal humeral fractures with medial calcar comminution: locking plate fixation alone and locking plate fixation with intramedullary allograft fibular bone peg augmentation. Method: Eight embalmed pairs of cadaveric specimens were utilized in this study. Dual energy X-ray absorptiometry (DXA) scans were initially performed to determine the bone density of the specimens. Surgical neck proximal humerus fractures were simulated in these specimens by creating a 1-centimeter wedge-shaped osteotomy at the level of the surgical neck to simulate medial calcar fracture comminution. Each pair of specimens had one arm randomly repaired with locking plate fixation, and the other arm repaired with locking plate fixation augmented with an intramedullary fibular autograft bone peg. The constructs were tested in bending to determine the failure loads, and initial stiffness using Digital Imaging Correlation (DIC) technology. The moment created by the rotator cuff was replicated by fixating the humeral head, and applying a point load to the distal humerus. A load was applied with a displacement rate of 4 mm/min, and was stopped approximately every 5 lbs to take a picture and record the load. This process was continued until failure of the specimens was obtained. Results: The intramedullary bone peg autograft increased the failure load of the constructs by 1.57±0.59 times (p = 0.026). Initial stiffness of the construct was also increased 3.13±2.10 times (p = 0.0079) with use of the bone peg. Conclusion: The stronger and stiffer construct provided by the addition of an intramedullary fibular allograft bone peg to locking plate fixation may help maintain reduction, and reduce the risk of fixation failure in surgical neck proximal humerus fractures with medial comminution.
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paper_title: Locking Plate Fixation with and without Inferomedial Screws for Proximal Humeral Fractures: A Biomechanical Study

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PURPOSE. To compare the efficacy of locking plate fixation with and without inferomedial screws in maintaining the reduction of a proximal humeral fracture. METHODS. 22 synthetic humerus models were used. A standardised 3-part proximal humeral fracture with a 4-mm wedge segment was created and fixed with a locking plate and screws with (n=11) and without (n=11) inferomedial screws. The intrafragmentary motion of the construct at 250, 500, 750, and 1000 cycles of 532 N loading, and the load to failure of the 2 groups were compared. RESULTS. Locking plate fixation with inferomedial screws reduced the mean intrafragmentary motion in all cycles (p<0.01) and increased the load to failure (1452 N vs. 1159 N, p<0.001), compared to fixation without inferomedial screws. CONCLUSION. Additional inferomedial screws provide medial column support for fracture healing. This may reduce intrafragmentary motion and thus implant complications resulting from varus malalignment such as screw perforation or loss of reduction.
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paper_title: Biomechanical analysis of plate osteosynthesis systems for proximal humerus fractures.

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OBJECTIVES ::: To biomechanically assess five proximal, humeral, fracture-plate-fixation systems. ::: ::: ::: METHODS ::: Surgical neck fractures, with and without cortical contact, were created in 25 fresh-frozen cadaveric humeri. Five methods of plate fixation were used for repair: construct A [an eight-hole, low contact dynamic compression (LCDC) plate contoured into a blade shape, supported by one, 70-mm-long, 4.5-mm-diameter cortical screw acting as a truss], construct B (a 10-hole LCDC plate arrangement identical to construct A, but using one, 70-mm-long, 3.5-mm-diameter cortical screw as a truss), construct C [a five-hole dynamic compression (DC) blade plate with one, 6.5-mm-diameter cancellous screw], construct D (a five-hole T-plate supported by three, 6.5-mm-diameter cancellous screws), and construct E (a five-hole cloverleaf plate supported by five, 4-mm-diameter cancellous screws). Plates were posterior to the bicipital groove, 10 mm distal to the greater tuberosity tip, on the lateral aspect of the humeral shaft. Screw fixation was done using standard AO compression plating techniques. Stiffness of constructs was measured in bending and axial compression. Locked plates were not assessed. ::: ::: ::: RESULTS ::: For cortical contact [abduction of 20 degrees (P=0.02), flexion of 20 degrees (P=0.02), flexion of 90 degrees (P=0.005)] and no cortical contact [flexion of 90 degrees (P=0.0001)], construct A was significantly stiffer than other constructs. For no cortical contact in abduction of 90 degrees (P=0.05), construct A was significantly stiffer than other constructs. ::: ::: ::: CONCLUSIONS ::: Construct A was significantly stiffer than other constructs.
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paper_title: The biomechanical performance of locking plate fixation with intramedullary fibular strut graft augmentation in the treatment of unstable fractures of the proximal humerus

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We evaluated the biomechanical properties of two different methods of fixation for unstable fractures of the proximal humerus. Biomechanical testing of the two groups, locking plate alone (LP), and locking plate with a fibular strut graft (LPSG), was performed using seven pairs of human cadaveric humeri. Cyclical loads between 10 N and 80 N at 5 Hz were applied for 1,000,000 cycles. Immediately after cycling, an increasing axial load was applied at a rate of displacement of 5 mm/min. The displacement of the construct, maximum failure load, stiffness and mode of failure were compared. The displacement was significantly less in the LPSG group than in the LP group (p = 0.031). All maximum failure loads and measures of stiffness in the LPSG group were significantly higher than those in the LP group (p = 0.024 and p = 0.035, respectively). In the LP group, varus collapse and plate bending were seen. In the LPSG group, the humeral head cut out and the fibular strut grafts fractured. No broken plates or screws were seen in either group. We conclude that strut graft augmentation significantly increases both the maximum failure load and the initial stiffness of this construct compared with a locking plate alone.
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paper_title: The Role of Medial Comminution and Calcar Restoration in Varus Collapse of Proximal Humeral Fractures Treated with Locking Plates

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Background: Proximal humeral fractures that are treated with locked plate constructs remain susceptible to collapse into a varus position. The objectives of the present study were to examine how medial comminution affects fracture stability and to determine the effect of calcar fixation on osteosynthesis stability. ::: ::: Methods: Eleven matched pairs of cadaveric humeri were osteotomized to create standard three-part fractures involving the surgical neck and the greater tuberosity. Five matched pairs were randomly assigned to have the medial calcar region remain intact. Six matched pairs had removal of a 10-mm medially based wedge of bone to simulate medial comminution. All fractures were stabilized in a uniform fashion with a proximal humeral locking plate. The constructs were secured, and the superior portion of the humeral head was subjected to compressive loading to induce varus collapse. Load-to-failure and energy-to-failure values along with stiffness and displacement at the time of failure were determined. ::: ::: Results: Medial comminution decreased the mean load to failure by 48% (523 N) (p = 0.015) and the mean energy to failure by 44% (2009 Nmm) (p = 0.013). The use of calcar screw fixation increased the mean load to failure by 31% (219 N) (p = 0.002) and the mean energy to failure by 44% (1279 Nmm) (p = 0.006). ::: ::: Conclusions: Medial comminution significantly decreased the stability of proximal humeral fracture fixation constructs. Calcar restoration with screw fixation significantly improved the stability of repaired fractures in cadaveric specimens. ::: ::: Clinical Relevance: The data suggest that medial comminution is a predictor of poor stability of proximal humeral fractures and that stability may be improved through calcar restoration.
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paper_title: Locking plates improve torsional resistance in the stabilization of three-part proximal humeral fractures.

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This study quantified the torsional resistance provided by locking plates and angled blade plates used to stabilize proximal humeral fractures. Three-part proximal humeral fractures were created in 6 pairs of cadaveric humeri. One specimen of each pair was reconstructed with a proximal humeral locking plate, whereas the other specimen was reconstructed with an angled blade plate. An external rotation torque, varying from 0 to 5 N-m, was applied to the humeral head until the head rotated 30 degrees or 10,000 loading cycles were applied. The mean initial torsional stiffness was significantly larger for the locking plates (0.99 N-m/degree) than for the blade plates (0.59 N-m/degree). For each pair, the maximum rotation was larger for the blade plate than for the locking plate. For this in vitro model of a reconstructed 3-part proximal humeral fracture, the locking plate provided better torsional fatigue resistance and stiffness than the blade plate.
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paper_title: Semitubular blade plate fixation in proximal humeral fractures: A biomechanical study in a cadaveric model

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This study was undertaken to compare the fixation of the semitubular blade plate with that of the AO T plate. Cadaveric humeri (n = 12 pairs) from an elderly population (41 to 89 years) had either a blade plate (n = 12) or a T plate (n = 12) fixed to them, subsequent to which a transverse osteotomy was performed. Mechanical testing in tension was performed in 1 series (n = 5, blade plate; n = 5, T plate) by applying a single maximal load to failure and in a second series (n = 7, blade plate; n = 7, T plate) by applying submaximal cyclic loading before failure was induced. Results showed that the fixation provided by the semitubular blade plate was significantly better (P <.05) than that of the T plate in those specimens subjected to submaximal cyclic loading before failure (series 2). This latter testing method contains some component of the clinical situation compared with monotonic distraction to failure. Based on these results plus favorable clinical results reported in the literature, the semitubular blade plate is possibly a better alternative to the T plate in the management of proximal humeral fractures that require open reduction and internal fixation. (J Shoulder Elbow Surg 1998;7:462-6.)
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paper_title: Medial support by fibula bone graft in angular stable plate fixation of proximal humeral fractures: an in vitro study with synthetic bone.

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BACKGROUND ::: Failure to achieve stable fixation with medial support in proximal humeral fractures can result in varus malalignment and cut-through of the proximal screws. The purpose of this study was to investigate the influence of an intramedullary fibula bone graft on the biomechanical properties of proximal humeral fractures stabilized by angular stable plate fixation in a bone model under cyclic loading. ::: ::: ::: METHODS ::: Two fixation techniques were tested in 20 composite analog humeri models. In group F- (n = 10), fractures were fixed by an anatomically formed locking plate system. In group F+ (n = 10), the same fixation system was used with an additional fibular graft model with a length of 6 cm inserted in an intramedullary manner. Active abduction was simulated for 400 cycles by use of a recently established testing setup. Fragment gap distance was measured, and thereby, intercyclic motion, fragment migration, and residual plastic deformation were determined. ::: ::: ::: RESULTS ::: The addition of a fibular graft to the fixation plate led to 5 times lower intercyclic motion, 2 times lower fragment migration, and 2 times less residual plastic deformation. Neither screw pullout, cut-through, nor implant failure was observed. ::: ::: ::: CONCLUSION ::: Medial support with an intramedullary fibular graft in an angular stable fixation of the proximal humerus in vitro increases overall stiffness of the bone-implant construct and reduces migration of the humeral head fragment. This technique might provide a useful tool in the treatment of displaced proximal humeral fractures, especially when there is medial comminution.
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paper_title: Biomechanical Analysis of Blade Plate Versus Locking Plate Fixation for a Proximal Humerus Fracture: Comparison Using Cadaveric and Synthetic Humeri

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Objective:To compare the mechanical stability of a fixed-angle blade plate with that of a locking plate in a cadaveric proximal humerus fracture-fixation model subjected to cyclic loading. A secondary objective was to evaluate whether the use of synthetic humerus specimens would replicate significan
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paper_title: Biomechanical comparison of a proximal humeral locking plate using two methods of head fixation.

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HYPOTHESIS ::: Locking plates have emerged as the implant of choice for stabilization of proximal humeral fractures. The biomechanical properties of a locked plating system using smooth pegs vs threaded screws for fixation of the humeral head were compared to test the hypothesis that there would be no biomechanical difference between pegs and threaded screws. ::: ::: ::: MATERIALS AND METHODS ::: Sixteen pairs of fresh frozen cadaveric humeri were randomized to have a surgical neck gap osteotomy stabilized with a locked plate using threaded screws (n=8) or smooth pegs (n=8). The intact contralateral humerus served as a control. Each specimen was tested with simultaneous cyclic axial compression (40 Nm) and torsion (both +/-2 Nm and +/-5 Nm) for 6000 cycles. All specimens were loaded to failure. Interfragmentary motion and load-displacement curves were analyzed to identify differences between the groups. Our data were then compared to previously published forces across the glenohumeral joint to provide evidence based recommendations for postoperative use of the shoulder. ::: ::: ::: RESULTS ::: There was a statistically significant difference between test specimens and their paired control (P < .001) in cyclic testing and load to failure. Differences between the smooth pegs and threaded screws were not statistically significant. ::: ::: ::: DISCUSSION ::: There is no biomechanical difference between locked smooth pegs and locked threaded screws for proximal fragment fixation in an unstable 2-part proximal humeral fracture model. ::: ::: ::: CONCLUSION ::: Our study contributes to the published evidence evaluating forces across the glenohumeral joint and suggests that early use of the affected extremity for simple activities of daily living may be safe. Use of the arm for assisted ambulation requiring a crutch, cane, walker, or wheelchair should be determined on a case-by-case basis.
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paper_title: A mechanical comparison between conventional and modified angular plates for proximal humeral fractures.

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The objective of this study is to present a modified angular blade plate for fixing 2-part and even 3-part fractures of the proximal humerus, as well as the results of the comparative mechanical test between the conventional angular blade plate and this new modified plate. The plates were tested in flexion and rotational trials in a wooden model that simulated a 2-part humeral fracture of the proximal extremity. The results (mean +/- SD) of bending strength and stiffness obtained after testing showed findings of 601 +/- 349 N and 0.5 +/- 0.2 N/mm, respectively, for the conventional plate and 4005 +/- 164 N and 3.9 +/- 0.7 N/mm, respectively, for the modified plate. The torsional stiffness test showed findings of 1.26 +/- 0.09 KN.mm degrees for the conventional plate and 1.74 +/- 0.21 KN.mm degrees for the modified plate. The test of torsional moment showed findings of 57.0 +/- 7.6 KN.mm for the conventional plate and 115.2 +/- 9.3 KN.mm for the modified plate. The test of angular displacement at the torsional moment showed findings of 50.8 degrees +/- 7.2 degrees for the conventional plate and 70.2 degrees +/- 2.6 degrees for the modified plate. The results of the mechanical trials of flexion and rotation were superior for the modified angular blade plate compared with the conventional angular blade plate.
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paper_title: BIOMECHANICAL EVALUATION OF PROXIMAL HUMERAL FRACTURE FIXATION SUPPLEMENTED WITH CALCIUM PHOSPHATE CEMENT

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Background: Proximal humeral fractures are common injuries, and numerous surgical methods have been described for their treatment. The biomechanical characteristics of various internal fixation devices that are used to treat these fractures have not been extensively studied, nor has the potential beneficial effect of calcium phosphate cement supplementation. Methods: We used a cadaveric three-part proximal humeral osteotomy model to perform a biomechanical evaluation of three types of internal fixation devices: a cloverleaf plate, an angled blade-plate, and Kirschner wires. The effect of supplementing the fixation with SRS (Skeletal Repair System) calcium phosphate cement was evaluated as well. Eighteen pairs of fresh-frozen humeri were obtained, and the bone-mineral density of each specimen was measured. In each pair, one specimen was secured with internal fixation alone and the contralateral specimen was secured with internal fixation combined with calcium phosphate cement. The specimens were tested cyclically in abduction and in external rotation for 250 cycles to evaluate interfragmentary motion. The specimens were then loaded to failure in external rotation to measure torsional load to failure and torsional stiffness. Results: Overall, there were no significant differences between the specimens treated with the blade and cloverleaf plates, whereas the specimens treated with Kirschner wires demonstrated more interfragmentary motion, less stiffness, and lower torque to failure. In general, supplementation with calcium phosphate cement led to significant improvements in the mechanical performance of all three forms of internal fixation as demonstrated by a significant decrease in interfragmentary motion, a significant increase in torque to failure, and a significant increase in torsional stiffness. The addition of calcium phosphate cement increased the stiffness of even the most osteoporotic specimens to levels that were higher than those of the most osteodense specimens that had been treated with internal fixation alone. Conclusion: The initial biomechanical properties of internal fixation as measured with use of a proximal humeral osteotomy model and three methods of fixation were significantly improved by the addition of calcium phosphate cement. Clinical Relevance: The addition of calcium phosphate cement may augment the mechanical characteristics of internal fixation of difficult, three-part proximal humeral fractures. The ability to stabilize the interface between the implant and cancellous bone, particularly in the presence of osteopenia, may make calcium phosphate cement a valuable clinical tool in the treatment of these difficult fractures.
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paper_title: Proximal humeral fracture fixation: locking plate construct ± intramedullary fibular allograft.

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BACKGROUND ::: Locking plate constructs for proximal humeral fractures can fail due to varus collapse, especially in osteoporotic bone with medial cortex comminution. Augmentation, using a fibular allograft as an intramedullary bone peg, may strengthen fixation preventing varus collapse. This study investigated the ability of the augmented locking plate construct to withstand repetitive varus stresses relative to the nonaugmented construct. ::: ::: ::: MATERIALS AND METHODS ::: Proximal humeral fractures with medial comminution were simulated by performing wedge-shaped osteotomies at the surgical neck in cadaveric specimens. For each cadaver (n = 8), 1 humeral fracture was fixated with the locking plate construct alone and the other with the locking plate construct plus ipsilateral fibular autograft augmentation. The humeral head was immobilized and a repetitive, medially directed load was applied to the humeral shaft until construct collapse or until 25000 cycles were completed. ::: ::: ::: RESULTS ::: No augmented construct collapsed. In comparison, 6 of 8 nonaugmented constructs collapsed (P < .05). Collapse in the 6 nonaugmented constructs occurred after an average ±SD of 6604 ± 1984 cycles. Screw penetration of the articular surface was found in only 1 of the nonaugmented constructs. ::: ::: ::: CONCLUSION ::: Fibular allograft augmentation increased the ability of the locking plate to withstand repetitive varus loading. Clinically, this may assist proximal humeral fracture fixation in osteoporotic bone with medial cortex comminution.
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paper_title: Monoaxial versus polyaxial locking systems: a biomechanical analysis of different locking systems for the fixation of proximal humeral fractures

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Objective ::: The development of locking plate systems has led to polyaxial screws and new plate designs. This study compares monoaxial head locking screws (PHILOS© by Synthes) and a new generation of polyaxial locking screws (NCB-LE© by Zimmer) with respect to biomechanical stability.
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Title: Biomechanical Analysis of Plate Systems for Proximal Humerus Fractures: A Systematic Literature Review

Section 1: Background
Description 1: Introduce the primary issue of proximal humerus fractures, current treatments, and the need for biomechanical analysis.

Section 2: Survey Methodology
Description 2: Outline the method used for the literature search and selection criteria for the included studies.

Section 3: Biomechanical Testing of Proximal Humerus Plates
Description 3: Discuss the types and prevalence of biomechanical tests performed on proximal humerus plates.

Section 4: Loading Conditions
Description 4: Describe the various loading conditions applied during the biomechanical tests, including axial loading, torsion, bending, and combined loading.

Section 5: Measurements and Data Analysis
Description 5: Explain the types of measurements taken during testing and how the data was analyzed, focusing on parameters like stiffness, load to failure, and interfragmentary motion.

Section 6: Comparison of Plate Technologies and Techniques
Description 6: Compare different plate systems and techniques, focusing on factors such as locking vs. non-locking screws, polyaxial vs. monoaxial screws, and the use of calcar support.

Section 7: Locking vs. Non-locking Screws
Description 7: Detail the biomechanical differences between locking and non-locking screw constructs.

Section 8: Polyaxial vs. Monoaxial Locking Screws
Description 8: Discuss the performance and potential advantages of polyaxial screw systems over monoaxial systems.

Section 9: Importance of Calcar Region
Description 9: Highlight the biomechanical significance of support in the medial calcar region.

Section 10: Rigid vs. Semi-rigid Plates
Description 10: Compare rigid and semi-rigid plate designs, emphasizing their mechanical properties and suitability for different patient populations.

Section 11: Cement Augmentation
Description 11: Review the use of cement augmentation to enhance the mechanical stability of plate constructs, especially in osteoporotic bone.

Section 12: Spatial Subchondral Support Plate
Description 12: Explore the biomechanical performance of the Spatial Subchondral Support Plate compared to other locking plates.

Section 13: Discussion
Description 13: Summarize the findings and address the three research questions guiding the review.

Section 14: Protocol Design for In Vitro Biomechanical Testing
Description 14: Provide recommendations for designing in vitro biomechanical tests that simulate in vivo conditions more accurately.

Section 15: Controversial Issues Relating to Proximal Humerus Plates
Description 15: Identify and discuss ongoing controversies in the biomechanical evaluation and clinical use of proximal humerus plates.

Section 16: Conclusions
Description 16: Conclude the review with key findings and suggest directions for future research and development.