The pelvis is a large semicircular bone complex that forms the base on which the torso and upper body are positioned. The pelvis, which is a rigid and inflexible portion of the skeleton, is built to provide a foundation of the movement of other parts of the anatomy, particularly the back and the legs. The pelvis also permits the weight of the entire upper body to be evenly distributed to the legs, which are connected to the pelvis through the hip joints. The pelvis is comprised of three bones arranged in a ring: the ilium, which is formed in the shape of a wing, rising on each side of the pelvis; the ischium, which forms the middle portion of the pelvis; and the pubis, the bone at the base of the pelvic structure. The pelvis is connected to the skeleton of the upper body by way of the sacroiliac, a fused joint at the connection between the lower portion of the spinal column and the pelvic bones.
The sacrum and the coccyx (the tailbone) are the bottom portion of the spine that make the connection to the pelvis; the presence of a ligament connecting the sacrum to the pelvis is not a typical joint, as the pelvic structure is capable of very little flexion or extension on its own. The pelvis also protects the lower organs of the abdomen, particularly those of the renal and intestinal tracts. Also important is the rigid and supportive structure of the pelvis, an essential aspect of the ability of the body to move dynamically through the legs. If the pelvis were less stable, the legs would not be able to generate either propulsion or their range of motion.
Abnormalities.—There is arrest of development in the bones of the pelvis in cases of extroversion of the bladder; the anterior part of the pelvic girdle is deficient, the superior rami of the pubes are imperfectly developed, and the symphysis is absent. “The pubic bones are separated to the extent of from two to four inches, the superior rami shortened and directed forward, and the obturator foramen diminished in size, narrowed, and turned outward. The iliac bones are straightened out more than normal. The sacrum is very peculiar. The lateral curve, instead of being concave, is flattened out or even convex, with the iliosacral facets turned more outward than normal, while the vertical curve is straightened.