Most pelvic fractures are secondary to automobile passenger or pedestrian accidents but are also the result of minor falls in older persons and from major falls or crush injuries. The mortality rate from all pelvic fractures is approximately 5%. However, with complex pelvic fractures, the mortality rate is about 20%.1 Isolated fractures of the pubic rami are likely in the elderly who sustain a low-energy mechanism of injury, such as falling off a chair, and are due to underlying fragility and osteopenia.2
ANATOMY AND BIOMECHANICS
The major functions of the pelvis are protection, support, and hematopoiesis. The pelvis consists of the sacrum and coccyx as well as the bilateral "innominate bones," which are comprised of three separate bones: the ischium, ilium, and pubis. These bones provide pelvic stability that is further supported by the strong posterior sacroiliac (SI), sacrotuberous, and sacrospinous ligaments (Figures 272-1 and 272-2). A small amount of pelvic stability is also provided by the pubic symphysis. The bladder lies in close proximity to the symphysis, as does the rectum to the sacrum, putting each of the structures at risk for injury in a trauma patient.
Bones and joints of the pelvis.
Incorporated in the pelvic structure are five joints that allow some movement in the bony ring. The lumbosacral, sacroiliac, and sacrococcygeal joints, as well as the symphysis pubis, allow little movement. The acetabulum is a ball-and-socket joint that is divided into three portions: the iliac portion, or superior dome, is the chief weight-bearing surface; the inner wall consists of the pubis and is thin and easily fractured; and the posterior acetabulum is derived from the thick ischium. Any single break in the ring will yield a stable injury without significant risk of displacement, whereas the occurrence of two breaks in the ring is considered an unstable pelvis.
The pelvis is extremely vascular. The iliac artery and venous trunks pass near the sacroiliac joints bilaterally. The nerve supply through the pelvis is derived from the lumbar and sacral plexuses. Injury to the pelvis may produce deficits at any level from the nerve root to small peripheral branches (Figure 272-3). The lower urinary tract is contained in the pelvis (Figure 272-4). In the adult, the bladder lies behind the symphysis and pubic bones, and the peritoneum covers the dome and base posteriorly. The location of the bladder and the degree of peritoneal reflection are determined by urine content. The lower GI tract housed in the pelvis includes a small portion of the descending colon, the sigmoid colon, the rectum, and the anus. In women, the uterus and vagina are also housed in the bony pelvis.