The hip is one of the body's largest joints. It is a ball-and-socket joint. The socket is formed by the acetabulum, which is part of the large pelvis bone. The ball is the femoral head, which is the upper end of the femur (thighbone). The most common cause of chronic hip pain and disability is arthritis. Osteoarthritis, rheumatoid arthritis, traumatic arthritis , AVN are the most common forms of this disease. In a total hip replacement (also called total hip arthroplasty), the damaged bone and cartilage is removed and replaced with prosthetic components. • The damaged femoral head is removed and replaced with a metal stem that is placed into the hollow center of the femur. The femoral stem may be either cemented or "press fit" into the bone. • A metal or ceramic ball is placed on the upper part of the stem. This ball replaces the damaged femoral head that was removed. • The damaged cartilage surface of the socket (acetabulum) is removed and replaced with a metal socket. Screws or cement are sometimes used to hold the socket in place. • A plastic, ceramic, or metal spacer is inserted between the new ball and the socket to allow for a smooth gliding surface..