The pelvis is a central part of the human skeleton, forming a basin-shaped structure at the base of the spine. While often perceived as a single bone, it is a complex assembly of several bones working together.
Locating the Pelvis
The pelvis is situated in the lower part of the torso, acting as a connection point between the lower spine and the upper leg bones. It forms the base of the trunk, resting between the abdomen and the thighs. This bony structure forms a complete ring, creating a protective basin. It supports the weight of the upper body and transfers this weight to the lower limbs.
Bones That Form the Pelvis
The pelvic girdle is comprised of four main bones that collectively form this ring-like structure. These include the two large, curved hip bones, also known as innominate bones. Each hip bone is formed from three smaller bones—the ilium, ischium, and pubis—that fuse during adolescence. Posteriorly, the hip bones connect to the sacrum, a spade-shaped bone at the base of the spine formed from five fused vertebrae. Inferior to the sacrum is the coccyx, or tailbone, a small, final bone at the tip of the spine.
Unique Aspects of the Female Pelvis
The female pelvis exhibits distinct structural differences compared to the male pelvis, primarily adapted to facilitate childbirth. It is generally broader and shallower, with a larger opening, or inlet, compared to the male pelvis. The pelvic inlet in females is typically rounded or oval-shaped, in contrast to the narrower, heart-shaped inlet often seen in males.
Another notable difference is the subpubic angle, which is the angle formed by the pubic bones at the front of the pelvis. In females, this angle is typically obtuse, ranging from 90 to 100 degrees, whereas in males it is more acute, less than 70 degrees. The female pelvis also features ischial tuberosities (sit bones) that are farther apart, contributing to a wider pelvic outlet.
Additionally, the female sacrum is generally shorter, wider, and more curved posteriorly, with a more movable coccyx. These adaptations collectively allow for the passage of a baby during delivery and provide support for the female reproductive organs.