Model of a traditional total knee replacement. The patella (knee cap) is not shown in this model. Photo courtesy: Department of Orthopaedics and Sports Medicine, University of Washington Medical Center

The first total knee replacement surgery was performed in 1968, and it has continued to evolve over the years due to improvements in surgical materials and techniques. Today, the prosthetic implant for a total knee replacement is composed of four parts: the tibial and femoral components, a plastic insert and the patella. The tibial and femoral components are made out of metal, usually cobalt chrome, and are used to cap the ends of the femur and tibia after the arthritic bone is removed. The plastic insert is made out of ultrahigh molecular weight polyethylene (UHMWPE) and fits into the tibial component, such that the highly polished surface of the femur glides against the plastic. The patella component is also made of UHMWPE, and glides against the front of the femoral component.