The efficient functioning of the hip joints is extremely important to the well being and mobility of the human body. Each hip joint is constituted by the upper portion of the upper leg bone (femur) which terminates in an offset bony neck surmounted by a ball-headed portion which rotates within a socket (acetabulum) in the hip bone. Diseases such as rheumatoid- and osteo-arthritis can cause erosion of the cartilage lining the acetabulum so that the ball of the femur and hip bone rub together causing pain and further erosion. Bone erosion causes the bones themselves to attempt to compensate and reshape, thus giving a misshapen joint which may well cease to function altogether.