What Is the Hip Bone?
The hip bones make up the bulk of the pelvis, and articulate with the femur. Each hip bone comprises roughly half of the pelvis, articulating with the sacrum in the back of the pelvis and with structures on the other hip bone in the front to create the pelvic girdle. Although people often think of the pelvis as a single fixed bone, it’s actually not: the pelvis consists of a number of smaller bones which fuse together as people grow up. During pregnancy, the joints between these bones actually loosen to allow the pelvis to expand so that it can accommodate the growing baby and the stress of labor and delivery. The three bones which comprise each hip bone are known as the innominate bones. The ileum is the largest innominate bone, making up the upper part of the hip bone. It joins with the ischium in the back and the pubis in the front to create the hip joint, with the ball of the femur fitting snugly into the bowl-like shape created by these three bones. At birth, the innominate bones
