Knee replacement for osteoarthritis. Front view X- ray of the knee of a 70 year old man showing the prostheses (white) implanted to treat osteoarthritis. This is a common disease in old age, caused by wear and tear eroding the cartilage lining of the joints. This causes the bones to rub together as the joint moves or bears weight, which causes pain, swelling and stiffness. Replacing the worn ends of the joint with implants restores mobility and reduces the pain. A metal cap is attached to the base of the femur (upper centre), and a plastic- capped implant is implanted into the top of the tibia. For this knee before the operation, see image M110/610. For a side view see images M110/609 (before) and M600/293 (after).