Hip replacement. Before and after X-rays of a double hip replacement, on a computer screen. The prosthetic hip joints can be clearly seen in the X-ray on the right (after). They consist of a shaft and ball attached to the top of the femur (thigh bone) and a socket (bright semi-circle above the ball) that is inserted into the pelvis. In the X-ray on the right (before), it is difficult to distinguish the joint due to osteoarthritis. Osteoarthritis is a degenerative joint disease that results in the loss of cartilage between the joint and the growth of bone in place of the cartilage. This causes pain, stiffness and loss of mobility.