hip, in human anatomy, the joint separating the thigh bone from the pelvis, and the surrounding flesh. The adult hipbone consolidates three bones separate in youth: the ilium, ischium, and pubis. The two prominences commonly called the hipbones are the crests of the ilia. The bones of the buttocks that support the seated body are projections of the ischia. At the body midline, fibrous tissue bands the two pubis bones, thus stabilizing the hips and preventing them from spreading or buckling. With maturity, the ilium, ischium, and pubis meet and grow together at a Y-shaped junction, the site of the acetabulum, a deep cavity that receives the rounded head of the thighbone, or femur. The resulting ball-and-socket joint allows great latitude of thigh movement. If arthritis affects the joint to such degree that medication and other therapies cannot sufficiently reduce pain and increase mobility, the hip may be replaced surgically, using a metal ball and stem implanted in the top of the thigh bone and an artificial socket secured in the pelvis. See also pelvis; leg.