Sunday, April 17, 2011

Pelvic girdle, pelvic floor muscles, hip fractures and incontinence

The pelvic girdle consists of right and left coxal bones (fusion of ilium, ischium and pubis) and the sacrum (fusion of 3-5 sacral vertebrae).  Structurally, it is very strong and rigid compared to the pectoral girdle which functionally differentiates it as well.  Instead of a large range of movement, the pelvic girdle supports the weight of the upper body, transmitting that weight from the axial region to the lower appendicular region.  The pelvic girdle provides attachment points for some of the muscles with the greatest mass in the body which are involved in locomotion.  The pelvic girdle contains the pelvic cavity which houses parts of the urinary tract, reproductive organs and the rectum.

There are many differences between the male and the female pelvis girdle.  The greater pelvis (area surrounded by iliac alae and superior aspect of S1) is deep in men and shallow in women, Figure 1.
Figure 1. Pelvic girdle differences between men and women.  1. Male 2. Female
The lesser pelvis (area surrounded by the right and left coxal bones, sacrum and coccyx) is narrow and deep in men and wide and shallow in women.  In men, the pelvic inlet is heart shaped and narrow and the pelvic outlet is small.  In women, the pelvic inlet is oval and rounded and the pelvic outlet is large, Figure 2, 3 and 4. 
Figure 2. Pelvic outlet differences between men and women.
Figure 3.  Differences in pelvic girdle between men and women.

Figure 4.  Pelvic inlet and outlet

The pubic arch is narrow, the obturator foramen is round, the acetabulum is large and the greater sciatic notch is narrow in men.  The pubic arch is wide, the obturator foramen is oval, the acetabulum is small and the greater sciatic notch is large in women, Figure 5 and 6.
Figure 5 Pelvic girdle

Figure 6. Pubic arch

The structural differences between the male and female pelvis are important for gynecological reasons and for forensic medicine and anthropology.  The shape and size of the female pelvis is gynecologically important for vaginal delivery of a fetus.  Dystocia is difficult and prolonged labor due to a small pelvis, big baby or slow cervical dilation.  A cesarian section may be performed if the pelvis is determined to be too small for vaginal delivery.  In forensic medicine and anthropology, the structural differences in the pelvic girdle are used to determine the sex of skeletal remains.

Pelvic bone fractures most often occur due to automobile accidents, falls and sports injuries (mainly sky diving and motor sports).  A severe fracture can cause damage to the bladder or rectum and internal bleeding.  Symptoms of a fracture include difficulty walking and hip, back and/or leg pain.  A severe fracture can cause dizziness, fainting, bloody stool, abdominal pain, leg weakness or numbness.  A fracture is treated by bed rest, anti-inflammatory medication and physical therapy.  A severe fracture is treated with surgery and may include placement of pins.  The incidence of pelvic bone fractures is low, with these fractures making up 3% of the total fracture incidents.

The pelvic floor, the most inferior boundary of the pelvic girdle, includes the muscles of the levator ani and the coccygeus muscle.  The muscles of the levator ani are from medial to lateral, the puborectalis, pubococcygeus and the iliococcygeus, Figure 7. 
Figure 7.  Pelvic floor muscles
Medial to these muscles is space allowing the urethra and vagina to pass through, called the urogenital hiatus.  The puborectalis muscle forms a u-shaped sling (puborectal sling) around the posterior part of the anorectal junction, Figure 8. 
Figure 8.  Puborectalis muscle.
The puborectalis muscle is important for maintaining fecal continence.  Together, the levator ani function to support the abdominopelvic viscera and for maintaining urinary and fecal continence.  These muscles actively contract during forced expiration, coughing, sneezing, vomiting and fixation of the trunk during lifting of heavy objects.  This increases the support to the abdominopelvic viscera when there is increased intra-abdominal pressure.  The levator ani relax during urination and defecation.

Incontinence is the involuntary excretion of urine and/or fecal matter.  Stress urinary incontinence (SUI) is due to weak pelvic floor muscles and/or urethral sphincter.  This causes the bladder to leak when pressure is put on the bladder or when intra-abdominal pressure is increased, such as during exercise, coughing, sneezing and laughing.   SUI commonly occurs after childbirth or menopause in women and after prostate cancer treatment in men.   SUI is the most common type of incontinence in women with incidence of 50% of incontinence.  Thirty percent of women who have SUI need to have surgery.  Some risk factors for SUI are pregnancy and childbirth, loss of muscle tone in pelvic muscles with aging, obesity, smoking, chronic coughing, repeated heavy lifting and high impact sports.  In men following radical prostatectomy, 5- 20% have SUI one year post surgery.  Treatment can include weight loss, stoping smoking, pelvic floor muscle exercises (Kegel exercises) and collagen injection.

National Association for Continence,
Moore, Keith L., Dalley, Arthur F. and Agur, Anne M., “Clincally Oriented Anatomy”, 6th ed., Wolters Kluwer, Lippincott Williams & Wilkins, 2010.


  1. just an addition:
    With the pelvic fractures most occur at the weakest points of the pelvis itself. Such as: the pubic rami, the acetabula, the sacroiliac joint, and the alae of the ilium. Like you noted surgery is used during these instances. Also the patient is to use crutches, a walker or even be put in a wheel chair for up to three months or until the bones have healed.

  2. Thanks Rachel, very interesting!