It's a smooth, round piece of bone covered by cartilage and fluid. The socket part of the hip joint in the pelvis matches the ball exactly. The joint is held together by muscles and ligaments. Sometimes through disease, stress or simply age, the cartilage covering the ball becomes damaged so the joint can't glide smoothly. This causes pain and stiffness.
Joint replacement can correct the problem.
When a joint needs to be replaced, the deteriorated bone and cartilage is removed from both the ball and socket. In the case of a hip replacement, a new socket made of high-impact plastic is implanted in the pelvis. A new ball, made of highly polished metal alloy, is implanted in the thigh bone. When, necessary, these new elements are cemented in place. The procedure lasts from one to three hours, and in most cases you'll be heading home four days after surgery.