In 1947, Shiers, a British Orthopaedic Surgeon, developed the first true knee joint replacement, which was a simple hinge joint, pivoting around a central pin. From this early design, other types of knee prostheses evolved, but they all functioned in much the same way as a basic hinge joint, with no attempt made to replicate the complex motion of a normal knee. This was primarily because there was little knowledge of the way in which a physiologically normal knee moves.
In most types of total knee replacement devices there are four parts:
a metal “femoral” component which is placed in the lower end of the femur
a metal “tibial” component which is placed on the upper end of the tibia
a plastic “insert” which is placed between the two metal components and effectively replaces the cartilage
a plastic “patella” component which is sometimes (though not always) used to resurface the back of the knee cap