Osteoarthritis. X-ray, on a computer screen, showing osteoarthritis in both hips. The hip joints are where the pelvis (centre) and the two femurs, or thigh bones (either side), meet. At the top of the femur is a ball, which fits into the socket of the hip. In a healthy individual there is usually a clear space between the two, but on this X-ray it is difficult to distinguish. Osteoarthritis results in the loss of cartilage between the joint. The healing process leads to the growth of bone in place of the cartilage, causing pain, stiffness and loss of mobility. This X-ray was taken prior to double hip replacement surgery.