Sex Differences of the Pelvis-Pelvic Joints Changes-Changes with Pregnancy-Changes with Age-Sacroiliac Joint Disease-

Sex Differences of the Pelvis

The sex differences of the bony pelvis are easily recognized.

The more obvious differences result from the adaptation of the female pelvis for childbearing. The stronger muscles in the male are responsible for the thicker bones and more prominent bony markings (Figs. 6.1 and 6.4).

■■ The false pelvis is shallow in the female and deep in the male.

■■ The pelvic inlet is transversely oval in the female but heart shaped in the male because of the indentation produced by the promontory of the sacrum in the male.

■■ The pelvic cavity is roomier in the female than in the male, and the distance between the inlet and the outlet is much shorter.

■■ The pelvic outlet is larger in the female than in the male.
 In the female the ischial tuberosities are everted and in the male they are turned in.

■■ The sacrum is shorter, wider, and flatter in the female than in the male.

■■ The subpubic angle, or pubic arch, is more rounded and wider in the female than in the male.

 

Pelvic Joints Changes

Changes with Pregnancy

During pregnancy, the symphysis pubis and the ligaments of the sacroiliac and sacrococcygeal joints undergo softening in response to hormones, thus increasing the mobility and increasing the potential size of the pelvis during childbirth. The hormones responsible are estrogen and progesterone produced by the ovary and the placenta. An additional hormone, called relaxin, produced by these organs can also have a relaxing effect on the pelvic ligaments.

Changes with Age

Obliteration of the cavity in the sacroiliac joint occurs in both sexes after middle age.

Sacroiliac Joint Disease

The sacroiliac joint is innervated by the lower lumbar and sacral nerves so that disease in the joint can produce low back pain and pain referred along the sciatic nerve (sciatica). The sacroiliac joint is inaccessible to clinical examination. However, a small area located just medial to and below the posterior superior iliac spine is where the joint comes closest to the surface. In disease of the lumbosacral region, movements of the vertebral column in any direction cause pain in the lumbosacral part of the column. In sacroiliac disease, pain is extreme on rotation of the vertebral column and is worst at the end of forward flexion. The latter movement causes pain because the hamstring muscles (see page 465) hold the hip bones in position while the sacrum is rotating forward as the vertebral column is flexed