The hip joint is composed of a ball and socket joint. The femoral head (ball) is the top of the femur (thigh bone) and the acetabulum (part of the pelvis) is the socket. These surfaces are both covevred by articular cartilage, which is a specialized lining allowing smooth pain free motion of the joint. Damage to this lining result in arthritis.

The joint is lined by a specialized synovial layer, which secretes fluid helping with lubrication....