What is involved during a total knee replacement?

With age, the weight-bearing surfaces of the knee joint become worn away. They are no longer smooth and free running, and this leads to stiffness and pain. Eventually, the joint wears away to such an extent that the bone of the femur grinds on the bone of the tibia. A total knee replacement replaces these surfaces with a metal alloy and a high-crosslinked polyethylene (plastic). The femoral replacement is a smooth metal resurfacing, similar to a crown on a tooth, which fits snugly over the end of the bone. The tibial replacement is in two parts, a metal base sitting on the bone and a plastic insert, which sits between the metal base on the tibial and femoral component. If necessary, the patellar surface (under the knee cap) is replaced with a plastic button, which glides over the metal surface of the femoral replacement. To replace the surface of the knee joint, a 20cm incision is made down the front of the knee and the joint opened. The bony overgrowth, which commonly occurs in arthritis of the knee, is trimmed away, and the joint surfaces removed. This involves some shaping of the bone so that the joint replacement components sit firmly on the bone. Bone cement may be used to hold the components in place.