10.14639/0392-100X-N0609
Introduction. The retrosigmoidal (RS) placement of the Bonebridge system (BB) has been advocated for cases of unfavourable anatomical or clinical conditions which contraindicate transmastoid-presigmoidal positioning. However, these disadvantageous conditions, combined with the considerable dimensions of the implant, may represent a challenge, especially for surgeons with no skull base experience. Moreover, the literature reports only limited experience concerning RS implantation of the BB system. Methods. A multicentre, retrospective study was conducted to analyse the surgical and functional outcomes of a wide population of patients undergoing RS placement of the BB system by means of a surgical technique specifically developed to overcome the intraoperative issues related to this surgery. Twenty patients with conductive or mixed hearing loss and single sided deafness were submitted to RS implantation of the BB system. Results. Audiological assessment concerning the measurement of the functional and effective gain by pure-tone audiometry (28 dB HL and -12.25 dB HL, respectively) and speech audiometry (24.7 dB HL and -21 dB HL, respectively) was conducted. A high overall subjective improvement of quality of life was recorded with the Glasgow Benefit Inventory questionnaire. No major complications, such as device extrusions or other conditions requiring revision surgery, were reported during the follow-up period (median: 42 months). Conclusions. In our study, which has one of the largest cohort of patients reported in the literature, RS placement of the BB system was safe and effective. Our functional results showed comparable hearing outcomes with presigmoidal placement. The effective gain, rarely investigated in this field, may be the object of further research to improve our understanding of bone conduction mechanisms exploited by bone conduction hearing implants.
application/xml
1827-675X
609
en
Marco Benazzo
https://creativecommons.org/licenses/by-nc-nd/4.0
ACTA Otorhinolaryngologica Italica
surgical technique
Retrosigmoidal placement of an active transcutaneous bone conduction implant: surgical and audiological perspectives in a multicentre study
Text.Serial.Journal
https://www.actaitalica.it/
41
Otology
2021-03-19
2020-01-15
2021-03-19
2021-03-24
91-99
1
Marco Benazzo
2021/03/19
10.14639/0392-100X-N0609
91
Department of Otorhinolaryngology, University of Pavia, Foundation IRCCS Policlinico “San Matteo”, Pavia, Italy
1827-675X
surgical technique
en
99
Retrosigmoidal placement of an active transcutaneous bone conduction implant: surgical and audiological perspectives in a multicentre study
https://www.actaitalica.it/article/download/609/529
41
ACTA OTORHINOLARYNGOLOGICA ITALICA 2021;41:91-99; doi: 10.14639/0392-100X-N0609




Otology


Retrosigmoidal placement of an active
transcutaneous bone conduction implant: surgical
and audiological perspectives in a multicentre study
Posizionamento retrosigmoideo di una protesi transcutanea attiva a conduzione
ossea: prospettive chirurgiche e audiologiche in uno studio multicentrico
Pietro Canzi1*, Irene Avato1,2*, Millo Beltrame1*, Giovanni Bianchin3, Marco Perotti4, Lorenzo Tribi3, Barbara Gioia4,
Federico Aprile1, Stefano Malpede1, Andrea Scribante5, Marco Manfrin1, Marco Benazzo1
1
  Department of Otorhinolaryngology, University of Pavia, Foundation IRCCS Policlinico “San Matteo”, Pavia, Italy; 2 PhD in
Experimental Medicine, University of Pavia, Italy; 3 Department of Otolaryngology and Audiology, Arcispedale Santa Maria Nuova -
IRCCS, Reggio Emilia, Italy; 4 Otorhinolaryngology Unit, Ospedale Civile “SS Antonio Biagio and C. Arrigo”, Alessandria, Italy; 5 Unit
of Orthodontics and Paediatric Dentistry-Section of Dentistry-Department of Clinical, Surgical, Diagnostic and Paediatric Sciences,
University of Pavia, Pavia, Italy
* P. Canzi, I. Avato and M. Beltrame contributed equally to this work


SUMMARY
Introduction. The retrosigmoidal (RS) placement of the Bonebridge system (BB) has been
advocated for cases of unfavourable anatomical or clinical conditions which contraindi-
cate transmastoid-presigmoidal positioning. However, these disadvantageous conditions,           Received: January 15, 2020
combined with the considerable dimensions of the implant, may represent a challenge,             Accepted: April 10, 2020
especially for surgeons with no skull base experience. Moreover, the literature reports only
limited experience concerning RS implantation of the BB system.                                  Correspondence
Methods. A multicentre, retrospective study was conducted to analyse the surgical and            Pietro Canzi
functional outcomes of a wide population of patients undergoing RS placement of the BB           University of Pavia, Department of Otorhinolaryn-
                                                                                                 gology, IRCCS Policlinico San Matteo Foundation,
system by means of a surgical technique specifically developed to overcome the intraopera-
                                                                                                 viale C. Golgi 19, 27100 Pavia, Italy
tive issues related to this surgery. Twenty patients with conductive or mixed hearing loss
                                                                                                 Fax +39 0382 528184
and single sided deafness were submitted to RS implantation of the BB system.                    E-mail: pietro.canzi@unipv.it
Results. Audiological assessment concerning the measurement of the functional and effec-
tive gain by pure-tone audiometry (28 dB HL and -12.25 dB HL, respectively) and speech           Funding
audiometry (24.7 dB HL and -21 dB HL, respectively) was conducted. A high overall sub-           None.
jective improvement of quality of life was recorded with the Glasgow Benefit Inventory
questionnaire. No major complications, such as device extrusions or other conditions re-         Conflict of interest
quiring revision surgery, were reported during the follow-up period (median: 42 months).         The Authors declare no conflict of interest.
Conclusions. In our study, which has one of the largest cohort of patients reported in the
literature, RS placement of the BB system was safe and effective. Our functional results
showed comparable hearing outcomes with presigmoidal placement. The effective gain,                How to cite this article: Canzi P, Avato I,
                                                                                                   Beltrame M, et al. Retrosigmoidal placement
rarely investigated in this field, may be the object of further research to improve our under-
                                                                                                   of an active transcutaneous bone conduction
standing of bone conduction mechanisms exploited by bone conduction hearing implants.              implant: surgical and audiological perspec-
KEY WORDS: bone conduction hearing implant, Bonebridge, transcutaneous,                            tives in a multicentre study. Acta Otorhi-
retrosigmoidal, surgical technique                                                                 nolaryngol Ital 2021;41:91-99. https://doi.
                                                                                                   org/10.14639/0392-100X-N0609

RIASSUNTO                                                                                        © Società Italiana di Otorinolaringoiatria
Introduzione. Il posizionamento retrosigmoideo del sistema Bonebridge (BB) è stato in-           e Chirurgia Cervico-Facciale
trodotto per ovviare alla presenza di condizioni anatomiche e cliniche che controindichino
l’alloggiamento del device in regione presigmoidea. Tuttavia, queste condizioni sfavorevo-                      OPEN ACCESS
li, associate alle considerevoli dimensioni dell’impianto, possono costituire un ostacolo per    This is an open access article distributed in accordance with
i chirurghi senza esperienza nell’ambito del basi-cranio. Inoltre, in letteratura sono pochi     the CC-BY-NC-ND (Creative Commons Attribution-Non-
gli studi riguardanti il posizionamento retrosigmoideo del sistema BB.                           Commercial-NoDerivatives 4.0 International) license. The
                                                                                                 article can be used by giving appropriate credit and mentio-
Metodi. Abbiamo svolto uno studio retrospettivo e multicentrico con lo scopo di analizzare       ning the license, but only for non-commercial purposes and
i risultati chirurgici e funzionali di un’ampia popolazione di pazienti sottoposti a posizio-    only in the original version. For further information: https://
namento retrosigmoideo del sistema BB tramite una specifica tecnica chirurgica che è stata       creativecommons.org/licenses/by-nc-nd/4.0/deed.en




                                                                                                                                                           91
P. Canzi et al.




sviluppata con lo scopo di superare i problemi intraoperatori relativi a questa chirurgia. Venti pazienti con ipoacusia di trasmissione o mista
e affetti da sordità monolaterale sono stati sottoposti a impianto retrosigmoideo del sistema BB.
Risultati. La valutazione audiologica ha riguardato la misurazione del guadagno funzionale ed effettivo in audiometria tonale (rispettivamen-
te pari a 28 dB HL e -12.25 dB HL) e audiometria vocale (rispettivamente pari a 24.7 dB HL e -21 dB HL). Globalmente è stato riportato un
significativo miglioramento soggettivo della qualità della vita rispetto alla condizione preoperatoria, quantificato mediante la compilazione
del questionario Glasgow Benefit Inventory. Non sono state riscontrate gravi complicanze o condizioni necessitanti una chirurgia di revisione
durante il periodo di follow-up (mediana: 42 mesi).
Conclusioni. Nell’ambito della nostra esperienza, risultata tra le più ampie mai riportate in letteratura, il posizionamento retrosigmoideo
del sistema BB si è dimostrato sicuro ed efficace. I nostri risultati funzionali hanno mostrato dati uditivi comparabili con il posizionamento
presigmoideo. Il guadagno effettivo, raramente indagato in questo campo della letteratura, potrebbe essere oggetto di future ricerche al fine di
migliorare la nostra comprensione dei meccanismi di conduzione ossea impiegati da questa tipologia di protesi impiantabili.
PAROLE CHIAVE: protesi impiantabile a conduzione ossea, Bonebridge, transcutaneo, retrosigmoideo, tecnica chirurgica



Introduction                                                              concerning RS implantation of the BB system, for which
In the 16 century, Girolamo Cardano first described the
             th                                                           surgical decision making faces many intraoperative chal-
transmission of sounds by bone conduction (BC) as an                      lenges, mainly related to the device dimensions 2,3,6-10. The
effective way to produce the sense of hearing 1. Based                    purpose of our study was to analyse surgical and function-
on audiological principles described many centuries ago,                  al outcomes in a wide population of patients undergoing
current BC hearing implants (BCHIs) result from the im-                   RS placement of the BB system by means of a surgical
pressive advances of the modern hearing industry and are                  technique specifically developed to overcome the intraop-
used for different types of hearing impairment: conduc-                   erative issues related to this surgery.
tive or mixed forms of hearing loss and single sided deaf-
ness (SSD) 2,3. BCHIs are mainly divided into two differ-                 Materials and methods
ent categories: skin-drive BCHIs and direct-drive BCHIs.
                                                                          Study design and participants
For the first type of device, the vibrations are transmitted
                                                                          A multicentre, retrospective case series study was conduct-
through intact skin, while in direct-drive BCHIs the vibra-
                                                                          ed on BCHI recipients who underwent RS placement of the
tions are sent directly to the bone via a screw attached to               BB system at three Otolaryngology tertiary referral centres
the skull (percutaneous BCHI) or an active transducer im-                 between January 2013 and September 2019. Approval from
planted into the bone (transcutaneous BCHI) 2. The active                 the local ethics committees was obtained and all patients
transcutaneous direct-drive systems have been developed                   signed informed consent agreements before treatment. All
to overcome the limits of percutaneous devices (skin irri-                patients met the audiological criteria suggested by the man-
tation or infections around the screw, fixture extrusion),                ufacturer: mild to moderate conductive hearing loss (CHL)
and to avoid the skin attenuation effects of skin-drive                   or mixed hearing loss (MHL) with pure tone average (PTA)
BCHIs. Nowadays, the Bonebridge® (Med-El, Innsbruck,                      BC threshold (0.5, 1, 2, 3 and 4 kHz) ≤ 45 dB HL and mini-
Austria) (BB) is the only active transcutaneous BCHI                      mum PTA air bone gap (ABG) of 30 dB, or SSD with a
available on the market, although another device has been                 better ear PTA air conduction (AC) threshold ≤ 20 dB HL.
in development since 2013 and is currently under regu-                    Moreover, enrolment criteria involved:
latory review 4,5. Three types of surgical placements are                 • conditions that contraindicate a presigmoid-transmas-
currently being performed for the BB housing. The most                       toid approach:
commonly used is transmastoid-presigmoid placement, in                       – anatomical (protruding sigmoid sinus, low-lying mid-
which the internal part is placed in the mastoid portion                        dle fossa dura, contracted mastoid bone);
of the temporal bone (sinodural angle) 6,7. The suprame-                     – clinical (chronical wet middle ear and mastoid cavity,
atal-middle fossa placement has been proposed in patients                       previous canal wall down mastoidectomy, aural atre-
with aural atresia and requires the drilling of the parietal                    sia scheduled for external ear reconstruction);
bone with complete exposure of the meninges. The lack                        – failure of previous hearing rehabilitation surgery (e.g.
of research on direct and long-term vibrations on the dura                      stapedotomy, tympanoplasty);
is in alignment with the authors’s recommendations for                       – inadequate hearing rehabilitation with conventional
long-term follow-ups 8. Retrosigmoidal (RS) placement                           hearing aids.
has proven to be useful in all patients in whom anatom-                   The preoperative assessment included a temporal bone CT
ical or clinical conditions contraindicate a presigmoidal                 scan and a brain MRI aimed at planning the surgical ap-
position 9. The literature reports only limited experience                proach and excluding comorbidities that may contraindi-



92
                                                                                     Retrosigmoidal placement of the Bonebridge system




cate surgery or require radiological follow-up. All audio-        a circular hole which diameter was smaller than the actual
metric tests were performed with an Inventis Piano Plus®          BC-FMT diameter (Fig. 1a,b).
audiometer. Preoperatively, pure-tone AC threshold from           A diamond burr was used to drill in the undercut position
0.125 to 8.0 kHz and pure-tone BC threshold from 0.25 to          to safely explore the circumference of the surgical site.
4.0 kHz were measured and the PTA (0.5, 1, 2, 4 kHz) was          Careful drilling was needed close to the sigmoid sinus. If
calculated. The speech reception threshold (SRT), at which        the sigmoid sinus was encountered, the circumference was
50% of the presented disyllabic words are recognised, was         enlarged step by step in a safer direction with the intent of
recorded in quiet conditions for both AC and BC. Postop-          obtaining the diameter required (Fig. 1c,d). The emissary
eratively, a pure tone audiometry and a speech audiometry         mastoid vein was closed if intercepted.
with disyllabic words in free field and quiet conditions were     A bony island between the BC-FMT and the dura mater
performed in both unaided (BB-OFF) and aided conditions           was shaped in order to reach a suitable depth for the BC-
(BB-ON). A noise masker by means of insert (at the non-           FMT housing when necessary. Once the bone layer was
test ear) was adopted to prevent cross hearing when nec-          obtained, it was separated from the underlying dura ma-
essary. As audiological outcomes, the functional gain (i.e.       ter using a freer dissector. The resulting surface could be
the difference between the postoperative unaided and aided        depressed, allowing complete lodging of the BC-FMT.
threshold) and the effective gain (i.e. the difference between    (Fig. 1e,f).
the BC threshold and the aided threshold) were evaluated          The T-sizer was used to verify the correct positioning of the
by pure-tone audiometry and speech audiometry. The first          BC-FMT, and the device was inserted and fixed with two
fitting was planned about 1 month after surgery. Audiologi-       self-tapping cortical screws. The anterior pedicle muscle-
cal follow-ups were scheduled at 3, 6, and 12 months and          periosteal flap was reconstructed with resorbable sutures
then yearly. The Glasgow Benefit Inventory (GBI) ques-            and the subcutaneous layer and the skin were then closed.
tionnaire was administered to each patient to evaluate items
regarding the quality of life after the surgery. It consists      Statistical analysis
of 18 questions, 12 of which apply to general health, 3 to        Statistical analysis were performed with R software (R
physical health and 3 to social health. For each question, 5      version 3.1.3, R Development Core Team, R Foundation
possible answers are available (scores ranging from 1 to 5).      for Statistical Computing, Wien, Austria). Descriptive sta-
Through a mathematical formula, four scores are then ob-          tistics were calculated for all groups (the mean, standard
tained: a total score and three partial scores (general health,   deviation, median, minimum and maximum values). Nor-
physical health and social health). Each score ranging from       mality of distributions was assessed with the Kolmogorov
-100 (worsening after surgery) through 0 (no change) to +         and Smirnov tests. An ANOVA test was ran to determine
100 (improvement after surgery) 11.                               whether significant differences existed among the groups.
                                                                  The Tukey test was used post-hoc. The Kruskal Wallis test
Surgical technique                                                was used to assess the statistical significance of each GBI
All the surgical procedures employed the same technique,          subscore. Significance for all statistical tests was predeter-
the steps of which are described below.                           mined at p < 0.05.
The conventional RS anatomical landmarks were identified
to allow the positioning of the internal implanted unit (the
BC floating mass transducer or BC-FMT) posteriorly to the
                                                                  Results
sigmoid sinus and superiorly to the digastric fossa, where        A total of 20 patients (11 males, 9 females, median age of
a regular bony surface was usually identified as the ideal        47.2 years) were included in the study. 13 patients were
location for the BC-FMT.                                          implanted on the right side and 7 on the left side. The aeti-
A retro-auricular reversed C-shaped incision was made             ology, type of hearing loss, and previous otologic and sur-
(4 cm-long incision) and an anteriorly pedicled C-shaped          gical history were investigated (Tab. I).
muscular-periosteal flap was harvested to enable access to
the bony area located above the digastric fossa and to create     Preoperative audiological assessment
a natural anatomical division between the mastoid cavity          10 patients with CHL (50%), 8 patients with MHL (40%)
and the BB housing. The subperiosteal pouch for the loca-         and 2 patients with SSD (10%) were identified; these latter
tion of the coil and the magnet was obtained under the flap.      two were not included in the statistical analysis of audio-
The probe (T-sizer) of the device was used to identify a          logical outcomes because surgery was performed to obtain
suitable area for the BC-FMT placement. In the centre of          a contralateral routing of signal. Mean PTA (18 out of 20
the marked area, the cortical bone was removed by shaping         patients) of the implant candidate’s ear was 61.5 dB HL



                                                                                                                                  93
P. Canzi et al.




Figure 1. Intraoperative images of the surgical steps and schematic representations. A cutting burr is used for the initial drilling (a), its diameter is smaller than
the actual diameter of the transducer as shown by the dotted line (a, b). An undercut drilling by means of a diamond burr is then executed to safely explore the
circumference of the surgical site and to create the housing for the device (c), this process is schematically represented (SS: sigmoid sinus) (d). A bony island is
sculpted to obtain a suitable depth for the housing of the device (e) and the dural layer is then detached by means of a freer dissector (f) to create a compress-
ible surface.




94
                                                                                                                       Retrosigmoidal placement of the Bonebridge system




Table I. Demographic data and otologic history.
 Patient    Sex     Age           Hearing loss                                  Pathology                         Previous surgery             Implanted             Bony
                                                                                                                      (BB side)                  side               island
 1              M         47             Bilateral MHL                  Bilateral cholesteatoma                        CWD TPL                    Right          Not required
 2              M         60             Bilateral MHL                  Bilateral cholesteatoma                        CWD TPL                    Right              Yes
 3              M         23             Bilateral CHL                 Atresia auris (BB side) +                        None                      Left               Yes
                                                                             cholesteatoma
 4              M         46           Bilateral MHL                         Bilateral COM                             CWU TPL                    Right                Yes
 5              F         52            Bilateral CHL                   Bilateral cholesteatoma                        CWD TPL                    Left                 Yes
 6              F         45                 SSD                             Cholesteatoma                             CWD TPL                    Right                Yes
 7              F         31            Bilateral CHL                    Bilateral atresia auris                         None                     Left                 Yes
 8              F         49           Bilateral MHL                Cholesteatoma (BB side) + COM                      CWD TPL                    Right                Yes
 9              M         47                 SSD                             Cholesteatoma                             CWD TPL                    Right                Yes
 10             F         61           Bilateral MHL                    Bilateral cholesteatoma                        CWD TPL                    Left                 Yes
 11             M         64           Bilateral MHL                         Bilateral COM                             CWU TPL                    Right          Not required
 12             M         76        MHL (BB side) + SNHL                     Cholesteatoma                       Lateral petrosectomy             Right                Yes
 13             F         67           Bilateral MHL                    Bilateral cholesteatoma                        CWD TPL                    Right                Yes
 14             F         14           Unilateral CHL                        Cholesteatoma                             CWD TPL                    Right                Yes
 15             M         37            Bilateral CHL                   Bilateral cholesteatoma                  Lateral petrosectomy             Left                 Yes
 16             F         33            Bilateral CHL                    Bilateral otosclerosis                      Stapedotomy                  Right                Yes
 17             M         39           Unilateral CHL               Cholesteatoma (BB side) + COM                Lateral petrosectomy             Right                Yes
 18             F         47        CHL (BB side) + MHL             Cholesteatoma (BB side) + COM                      CWD TPL                    Right                Yes
 19             M         57        CHL (BB side) + SNHL               Cholesteatoma (BB side)                         CWD TPL                    Left                 Yes
 20             M         48                 CHL                             Cholesteatoma                             CWU TPL                    Left          No (lifts 2 mm)
M: male; F: female; CHL: conductive hearing loss; MHL: mixed hearing loss; SNHL: sensorineural hearing loss; SSD: single sided deafness; BB: Bonebridge; COM: chronic otitis media;
CWD: canal wall down; CWU: canal wall up; TPL: tympanoplasty



(range 41.25-83.75 dB HL, SD: ± 13.07) for AC, 20.5 dB                                      and the BB-ON PTA) was -12.25 dB HL (range -27.5-0 dB
HL (range 6.25-33.75 dB HL, SD: ± 8.72) for BC. The                                         HL, SD: ± 8.82) (Fig. 3). The effective gain distribution was
ABG calculated on the PTA was 41 dB HL (range 28.75-                                        also selectively analysed at low (0.25, 0.5 kHz), mid (1, 2
56.25 dB HL, SD: ± 7.58). Regarding speech audiometry                                       kHz) and high frequencies (4 kHz) and resulted in -26.25 dB
on the implant candidate’s ear, the mean AC SRT was 67.85                                   HL (SD: ± 5.8), -4.29 dB HL (SD: ± 6.56) and -18.57 dB
dB HL (range 55-90 dB HL, SD: ± 13.4); BC SRT was                                           HL (SD: ± 9.07) respectively. The mean effective gain cal-
20.35 dB HL (range 10-40 dB HL, SD: ± 9.49). The ABG                                        culated via speech audiometry was -21 dB HL (range -30-0
SRT for the implanted side was 47.5 dB HL (range 30-70                                      dB HL, SD: ± 8). During the follow-up (median: 42 months;
dB HL, SD ± 10.51) (Fig. 2).                                                                range: 11-72 months) no worsening of the BC threshold
                                                                                            occurred. About 3 months after the first fitting, a stability
Postoperative audiological assessment                                                       of the audiological gain values was observed and then con-
Postoperatively, in the BB-OFF setting, AC PTA was 60.8                                     firmed at subsequent evaluations. The ANOVA and Tukey
dB HL (range 41.25-83.75 dB HL, SD: ± 12.22). The PTA                                       tests were ran to determine the presence of significant differ-
threshold improved to 32.75 dB HL in the BB-ON setting                                      ences (p < 0.05) between BB-ON thresholds and BB-OFF
(range 11.25-45 dB HL, SD: ± 8.29). The mean functional                                     thresholds (functional gain) and between BB-ON thresholds
gain on pure-tone audiometry was 28 dB HL (range 13.75-                                     and BC thresholds (effective gain). Specifically, pure-tone
45 dB HL, SD: ± 10.54). Concerning speech audiometry, the                                   BB-ON and BB-OFF thresholds were compared considering
mean BB-OFF SRT was 66 dB HL (range 40-90 dB HL, SD:                                        all frequencies between 0.25 kHz and 4 kHz. A significant
± 13.32) improving up to 41.35 dB HL in the BB-ON setting                                   difference was found for each frequency tested (p < 0.05).
(range 30-65 dB HL, SD: ± 9.54). The mean functional gain                                   Functional gain was found significant (p < 0.05) by speech
as analysed via speech audiometry was 24.7 dB HL (range                                     audiometry when BB-ON SRTs were compared with BB-
10-36 dB HL, SD: ± 8.74 – Fig. 3). The mean pure-tone ef-                                   OFF SRTs. Focusing on the effective gain analysed via pure-
fective gain (i.e. the mean difference between the BC PTA                                   tone audiometry, a significant difference (p < 0.05) was seen



                                                                                                                                                                               95
P. Canzi et al.




                                                                                                    AC: air conduction threshold; BC: bone conduction threshold.


Figure 2. Preoperative mean audiograms of implant candidate’s ear: pure-tone audiometry (vertical bars: standard deviation) and speech audiometry (horizontal
bars: standard deviation).




Figure 3. Mean free field aided threshold (BB-ON) compared with the free field unaided threshold (BB-OFF): pure-tone audiometry (vertical bars: standard de-
viation) and speech audiometry (horizontal bars: standard deviation). BC: bone conduction threshold. Light grey highlighted area: mean functional gain (i.e. the
difference between the postoperative unaided and aided threshold). Dark grey highlighted area: mean effective gain (i.e. the difference between the BC threshold
and the aided threshold). A noise masker by means of insert (at the contralateral ear) was adopted when necessary.


between BB-ON thresholds and BC thresholds at 0.25, 0.5                           tions included a single case of dural dehiscence that was re-
and 4 kHz (Fig. 4a,c). Conversely, a significant difference                       paired with autologous fascia. Postoperative sensorineural
was not found at 1 and 2 kHz (p > 0.05) (Fig. 4b). An overall                     hearing worsening or vestibular symptoms were never ob-
statistically significant difference (p < 0.05) was found when                    served. At the time of follow-up, none of the BB recipients
BB-ON SRTs were compared with BC thresholds (Fig. 4d).                            experienced device extrusions or other conditions requiring
                                                                                  revision surgery.
Surgery and complications
The device was correctly placed in the designated RS surgi-                       Quality of life assessment
cal area in all patients and it was possible to fix the implant                   Concerning the GBI questionnaire, descriptive statistics
with both screws. Specifically, a bony island was sculpted                        are showed in Table II. Patients showed general, physical
in 17 patients (85%) and lifts were used in 1 patient (5%),                       and social health gain (p < 0.05; Fig. 5) and no significant
while the implant was directly lodged in 2 patients (10%).                        differences were reported among the various subcategories
No major complications were observed. Minor complica-                             (p > 0.05).



96
                                                                                                         Retrosigmoidal placement of the Bonebridge system




Figure 4. ANOVA test applied to compare the free field aided thresholds (BB-ON) with the free field unaided thresholds (BB-OFF) and with bone conduction
(BC) thresholds. a) Pure-tone audiometry – low frequencies b) Pure-tone audiometry – mid frequencies; c) Pure-tone audiometry – high frequencies; d) Speech
audiometry – speech recognition threshold (SRT). All graphs show a significant difference (p < 0.05) when the BB-ON thresholds are compared with the BB-OFF
thresholds. All graphs show a significant difference (p < 0.05) when the BB-ON thresholds are compared with the BC thresholds with the exception of the mid-
frequencies graph. Vertical bars: standard deviation.


Table II. Glasgow Benefit Inventory descriptive statistics.
                  Mean          SD        Min         Median      Max
 Total score          49.40   19.54        10        55.5          83
 General              55.65   17.88        15        58.5          92
 health
 Physical             41.70   27.63       -15         42           84
 health
 Social health        34.60   32.09       -33         50           80
SD: standard deviation.



Discussion
Our study presents one of the largest samples of patients
submitted to RS implantation of the BB system reported in
literature. The sample is highly homogeneous in terms of                        Figure 5. Results of the Glasgow Benefit Inventory (GBI) questionnaire. The
                                                                                histogram provides a graphic representation of the quality of life after surgery
surgical technique and audiological assessment. First de-                       reporting the mean GBI total and partial scores (horizontal bars: standard de-
scribed by Sprinzl et al. in a European multicentre study 12,                   viation). Scores can range from – 100 (worsening after surgery) through 0
RS placement has been advocated in case of unfavourable                         (no change) to + 100 (improvement after surgery). A significant improvement
anatomical or clinical conditions which contraindicate the                      (p < 0.05) is shown for each GBI score and no significant differences are re-
                                                                                ported among the various subcategories (p > 0.05).
presigmoidal position 9,13,14. However, these disadvanta-
geous conditions combined with the considerable dimen-
sions of the internal implanted unit (8.7 mm in thickness                       drilling (especially close to the sigmoid sinus). It also pre-
and 15.8 mm in diameter) and with the topography of the                         vents over-extension of the drilling surface which could
anatomical area addressed to the BC-FMT housing, make                           compromise fixation of screws. In all BB recipients, the
this surgical procedure challenging 7,15-17. In alignment with                  surgical procedure was successfully performed with a com-
data from the literature, medical history of previous mid-                      plete lodging of the BC-FMT and with its fixation with two
dle ear surgery represented the main eligibility criteria for                   self-tapping screws. None of the patients required revision
a RS position 9 in our study. The harvesting of an ante-                        surgery or BB explantation. A bony island was sculpted in
riorly pedicled muscular-periosteal flap was developed to                       85% of patients, allowing adequate BC-FMT housing and
prevent possible contaminations from the mastoid cavity                         concurrent protection of the dura from major complications
and middle ear towards the site of implantation. The sur-                       both intra- and postoperatively. Brkic et al. 18 recently re-
gical technique was designed to obtain an adequate bony                         ported one of the largest studies of patients submitted to BB
bed for the BC-FMT housing, while avoiding hazardous                            implantation, analysed over a 6-year follow-up period. In



                                                                                                                                                            97
P. Canzi et al.




their experience, the authors observed an overall complica-       to limit the BB fitting range on certain frequencies are un-
tion rate of 9.4% including 5 cases of explantation. Inter-       pleasant sound distortions and annoying vibratory percep-
estingly, 3 of these implants were positioned in a radical        tions 26. The RS placement itself, does not seem to be related
cavity, which was subsequently compromised by postop-             to these findings, since our audiological results have shown
erative infections. According to the authors, a presigmoidal      to be comparable with current literature data for presigmoid
approach is to be preferred even in patients with history of      positioning. Furthermore, a significant improvement in the
previous radical cavities because of anatomical factors lim-      quality of life was recorded in all patients as suggested by
iting RS placement. Furthermore, the same tertiary referral       the total and partial GBI scores. We are, nonetheless, aware
centre published a previous study of 19 patients in which         that some concerns regarding our study may arise. The ret-
the BC-FMT was directly coupled to the dura or sinus (7           rospective and multicentric nature of the study may be con-
RS placements, 12 presigmoidal/middle fossa placements).          sidered a limitation in terms of heterogeneity of the series.
Although no adverse events were reported, the authors clar-       However, the adoption of common enrolment criteria and a
ified that the risks of direct sinus/dura compression are not     standardised surgical technique and the uniformity of data
yet clear 19.                                                     analysis minimise this bias. Additionally, the introduction
In our experience, the surgical technique was designed to         of an uncommonly used audiological measurement such as
overcome the abovementioned issues and to reduce the pos-         the effective gain may preclude comparison with the cur-
sibility of revision surgery or long-term untoward events.        rent literature.
Considering audiological findings, all patients enrolled
met the preoperative recommended criteria: specifically,          Conclusions
mean BC PTA was 20.5 dB, almost 25 dB lower than the
manufacturer’s indications. The effectiveness of BCHI was         RS placement of the BB system was seen to be safe and
investigated by means of two audiological measurements:           effective, thus constituting in a valid surgical alternative
functional and effective gain. The mean PTA functional            when the presigmoidal position is not advised. However, it
gain was found to be 28 dB HL, consistent with the results        may represent a challenge, especially for surgeons with no
reported in the two largest series of RS implanted patients       skull base experience. The surgical technique introduced
(28.9 dB and 28 dB in Ihler et al. 20 and Loader et al. 14        was developed to define the main surgical steps of RS
respectively). With regards to presigmoidal placement, our        placement in order to obtain a complete lodging of the in-
data did not reveal a significant difference in terms of mean     ternal implanted unit, avoiding untoward events both intra-
functional gain (Gerdes et al. 21 27.5 dB; Riss et al. 22 28.8    and postoperatively, even after long-term follow-up. Our
dB). Although debated in literature, superior audiological        functional results show comparable hearing outcomes with
effectiveness cannot be assessed using currently published        presigmoidal placement, in contrast to authors who argue
data when the two BC-FMT surgical placements are com-             a greater efficacy of one of the two positions. The effective
pared 14,19,23,24. The effective gain is considered expression    gain, rarely investigated in this field of literature, may be
of the relationship between the threshold in aided condition      object of future research to improve our understanding of
and the patient’s cochlear reserve. Defined as the difference     BC mechanisms exploited by the BCHIs.
between the BC threshold and the aided threshold, the ef-
fective gain may result in negative values and if positive,
indicates ABG overclosure. This parameter was previously          References
measured by Donnelly et al. 25 to evaluate the effectiveness      1
                                                                      Berger KW. Early bone conduction hearing aid devices. Arch
of different types of active middle ear implants and by van           Otolaryngol       1976;102:315-8.      https://doi.org/10.1001/archo-
Barneveld et al. 26 to define fitting ranges for BC devices. To       tol.1976.00780100101017
the best of our knowledge, only one study has reported this       2
                                                                      Reinfeldt S, Håkansson B, Taghavi H, et al. New developments in
parameter in BCHI recipients 18, although it was not object           bone-conduction hearing implants: a review. Med Devices (Auckl)
                                                                      2015;8:79-93. https://doi.org/10.2147/MDER.S39691
of further analysis. In our experience, the mean pure-tone        3
                                                                      Canale A, Boggio V, Albera A, et al. A new bone conduction hearing
effective gain was -12.25 dB HL, although it showed a dif-            aid to predict hearing outcome with an active implanted device. Eur
ferent statistical distribution when selectively analysed at          Arch Otorhinolaryngol 2019;276:2165-70. https://doi.org/10.1007/
low, mid and high frequencies. In particular, the highest             s00405-019-05450-4
values were measured at 1-2 kHz (-4.29 dB HL) where a
                                                                  4
                                                                      Eeg-Olofsson M, Håkansson B, Reinfeldt S, et al. The bone con-
                                                                      duction implant – first implantation, surgical and audiologic as-
significant difference between the BB-ON thresholds and               pects. Otol Neurotol 2013;35:679-85. https://doi.org/10.1097/
the BC thresholds was not found. These observations, ap-              MAO.0000000000000203
parently, do not relate to power output issues. What seems        5
                                                                      Håkansson B, Reinfeldt S, Persson AC, et al. The bone conduction




98
                                                                                                        Retrosigmoidal placement of the Bonebridge system




     implant – a review and 1-year follow-up. Int J Audiol 2019;58:945-         16
                                                                                     Canzi P, Marconi S, Manfrin M, et al. From CT scanning to 3D print-
     55. https://doi.org/10.1080/14992027.2019.1657243                               ing technology: a new method for the preoperative planning of a
6
     Sprinzl GM, Wolf-Magele A. The Bonebridge Bone Conduction                       transcutaneous bone-conduction hearing device. Acta Otorhinolaryn-
     Hearing Implant: indication criteria, surgery and a systematic re-              gol Ital 2018;38:251-6. https://doi.org/10.14639/0392-100X-1625
     view of the literature. Clin Otolaryngol 2016;41:131-43. https://doi.      17
                                                                                     Law EKC, Bhatia KSS, Tsang WSS, et al. CT pre-operative plan-
     org/10.1111/coa.12484                                                           ning of a new semi-implantable bone conduction hearing device. Eur
                                                                                     Radiol 2016;26:1686-95. https://doi.org/10.1007/s00330-015-3983-x
7
     Wimmer W, Gerber N, Guignard J, et al. Topographic bone thick-
     ness maps for Bonebridge implantations. Eur Arch Otorhinolaryngol          18
                                                                                     Brkic FF, Riss D, Scheuba K, et al. Medical, technical and audiologi-
     2015;272:1651-8. https://doi.org/10.1007/s00405-014-2976-8                      cal outcomes of hearing rehabilitation with the bonebridge transcu-
                                                                                     taneous bone-conduction implant: a single-center experience. J Clin
8
     Der C, Bravo-Torres S, Pons N. Active transcutaneous bone
                                                                                     Med 2019;8:1614. https://doi.org/10.3390/jcm8101614
     conduction implant: middle fossa placement technique in chil-
     dren with bilateral microtia and external auditory canal atre-
                                                                                19
                                                                                     Vyskocil E, Riss D, Arnoldner C, et al. Dura and sinus compression
     sia. Otol Neurotol 2018;39:342-8. https://doi.org/10.1097/                      with a transcutaneous bone conduction device – hearing outcomes
     MAO.0000000000001809                                                            and safety in 38 patients. Clin Otolaryngol 2017;42:1033-8. https://
                                                                                     doi.org/10.1111/coa.12793
9
     Lassaletta L, Sanchez-Cuadrado I, Muñoz E, et al. Retrosigmoid im-
     plantation of an active bone conduction stimulator in a patient with
                                                                                20
                                                                                     Ihler F, Blum J, Berger MU, et al. The prediction of speech rec-
     chronic otitis media. Auris Nasus Larynx 2014;41:84-7. https://doi.             ognition in noise with a semi-implantable bone conduction hear-
     org/10.1016/j.anl.2013.04.004                                                   ing system by external bone conduction stimulation with head-
                                                                                     band: a prospective study. Trends Hear 2016;20:1-12. https://doi.
10
     Barbara M, Perotti M, Gioia B, et al. Transcutaneous bone-conduc-               org/10.1177/2331216516669330
     tion hearing device: audiological and surgical aspects in a first series   21
                                                                                     Gerdes T, Salcher RB, Schwab B, et al. Comparison of audiological
     of patients with mixed hearing loss. Acta Otolaryngol 2013;133:1058-
                                                                                     results between a transcutaneous and a percutaneous bone conduction
     64. https://doi.org/10.3109/00016489.2013.799293
                                                                                     instrument in conductive hearing loss. Otol Neurotol 2016;37:685-91.
11
     Robinson K, Gatehouse S, Browning GG. Measuring pa-                             https://doi.org/10.1097/MAO.0000000000001010
     tient benefit from otorhinolaryngological surgery and thera-               22
                                                                                     Riss D, Arnoldner C, Baumgartner WD, et al. Indication criteria
     py. Ann Otol Rhinol Laryngol 1996;105:415-22. https://doi.                      and outcomes with the Bonebridge transcutaneous bone-conduction
     org/10.1177/000348949610500601                                                  implant. Laryngoscope 2014;124:2802-6. https://doi.org/10.1002/
12
     Sprinzl G, Lenarz T, Ernst A, et al. First European multicenter results         lary.24832
     with a new transcutaneous bone conduction hearing implant system:          23
                                                                                     Salcher R, Zimmermann D, Giere T, et al. Audiological results in
     short-term safety and efficacy. Otol Neurotol 2013;34:1076-83. htt-             SSD with an active transcutaneous bone conduction implant at a
     ps://doi.org/10.1097/MAO.0b013e31828bb541                                       retrosigmoidal position. Otol Neurotol 2017;38:642-7. https://doi.
13
     Lassaletta L, Calvino M, Zernotti M, et al. Postoperative pain in pa-           org/10.1097/MAO.0000000000001394
     tients undergoing a transcutaneous active bone conduction implant          24
                                                                                     Schmerber S, Deguine O, Marx M, et al. Safety and effectiveness of
     (Bonebridge). Eur Arch Otorhinolaryngol 2016;273:4103-10. https://              the Bonebridge transcutaneous active direct-drive bone-conduction
     doi.org/10.1007/s00405-016-3972-y                                               hearing implant at 1-year device use. Eur Arch Otorhinolaryngol
14
     Loader B, Sterrer E, Reichmayr C, et al. Direct comparison of mas-              2017;274:1835-51. https://doi.org/10.1007/s00405-016-4228-6
     toidal and retrosigmoidal placement of a transcutaneous bone conduc-       25
                                                                                     Donnelly NP, Pennings RJE. Hearing rehabilitation with active mid-
     tion device after canal wall down tympanoplasty. Clin Otolaryngol               dle ear implants. Adv Otorhinolaryngol 2018;81:43-56. https://doi.
     2018;43:1603-6. https://doi.org/10.1111/coa.13187                               org/10.1159/000485529
15
     Bianchin G, Bonali M, Russo M, et al. Active bone conduction sys-          26
                                                                                     Van Barneveld DCPBM, Kok HJW, Noten JFP, et al. Determining fit-
     tem: outcomes with the Bonebridge transcutaneous device. ORL                    ting ranges of various bone conduction hearing aids. Clin Otolaryngol
     2015;77:17-26. https://doi.org/10.1159/000371425                                2018;43:68-75. https://doi.org/10.1111/coa.12901




                                                                                                                                                      99
