Osteoarthritis. X-ray of the hip joint (centre) of a 75 year old woman with osteoarthritis. The pelvis is at top and right, the head of the femur (thigh bone) is at bottom left to centre. The ball at the top of the femur fits into the socket of the hip. In a healthy individual there is usually a clear space between the ball and socket, but this joint shows little or no space. 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. Treatment is with the surgical replacement of the joint. For an image showing the surgery for this patient see M551/450 to M551/460.