Total knee joint replacement. Coloured X-ray of the knee of an adult man (side view) showing an artificial (prosthetic) joint replacing the knee joint. This metal alloy implant, screwed in place, runs much of the length of the leg bones it helps to support. At lower centre, the prosthesis (green) forms a hinged knee joint. The implant attaches to the femur (thigh bone, upper frame) and to the tibia (shin bone, lower frame). It forms a flexible joint, relieving joint pain and immobility. Knee joint replacement is conducted usually because of joint disease such as osteo- arthritis or due to injury. The kneecap (patella bone) is at lower left.