Last updated: 11/24/2009

Knee revision surgery has three major purposes: relieving pain in the affected hip; restoring the patient's mobility; and removing a loose or damaged prosthesis before irreversible harm is done to the joint. Knee prostheses can come loose for one of...

two reasons. One is mechanical and is related to the fact that the knee joint bears a great deal of weight when a person is walking or running. It is unusual for the metal part of a knee prosthesis to simply break. This part, however, is inserted into the upper part of the tibia, the larger of the two bones in the lower leg, after the surgeon has removed the upper surface of the tibia. The bone tissue that receives the metal implant is softer than the bone that was removed, which means that the metal implant may sink into the softer bone and gradually loosen.

The second reason for loosening of a knee prosthesis is related to the development of inflammation in the knee joint. The plastic part of a knee prosthesis is made of a material called polyethylene, which can form small particles of debris as a result of wear on the prosthesis over time. If the patient has an uneven gait, or pattern of walking, the debris particles tend to form at a faster rate because one side of the prosthesis will tend to pull away from the bone and the other side will be pushed further into the bone. These tiny fragments of plastic are absorbed by tissue cells around the knee joint, which become inflamed. The inflammatory response begins to dissolve the bone around the prosthesis in a process known as osteolysis. As the osteolysis continues, bone loss accelerates and the prosthesis eventually comes loose.

A knee prosthesis that has become infected or completely dislocated must be removed and replaced to prevent permanent damage to the patient's knee.