The hip is where the top of the leg (femur) joins the pelvis. The joint allows free movement of the leg. It is important because the femur is your largest bone and your thigh muscles are the most powerful. You rely heavily on this joint working to get about.

The joint is a ball and socket type. The top of the thigh bone ends in a ball, which fits nicely into a socket shape in the pelvis. The socket is lined with cartilage to allow the ball to move about easily. If the cartilage becomes worn or diseased, the ball and socket will grind together and the patient will suffer pain and a loss of movement as a result.

This condition is often seen in older people as a simple result of a lifetime of wear and tear. It can also be caused by osteoarthritis, which is again more common in older people. One solution is to replace the hip joint altogether. About 120,000 such operations are carried out in the USA each year.

The procedure uses either a general or regional anaesthetic. The Orthopedic surgeon takes the ball out of the socket. The damaged or diseased cartilage is removed and replaced by a man-made cup or socket. The ball shape at the head of the femur is broken off and replaced by a new ball which is fitted securely onto the femur and into the new cup.

The new cup and ball can be made of metal, ceramic or plastic. The joins with the natural body can be cemented using a man-made substance to provide the adhesion. Alternatively, the new cup and ball may have small gaps in them designed to encourage the natural bone to grow into and join with the man-made parts.

Many people have both hips replaced.