The most important part of the implant is the bearing surface. This is the smooth, polished part of the implant that articulates at the level of the joint, allowing the low-friction motion which is required to walk normally. Over time, surgeons have tried many different combinations of bearing surfaces, each of which has certain advantages and drawbacks. The most predictable results are found using bearing surfaces that have stood the test of time, and have demonstrated decades-long survivorship in longitudinal registry studies.
The knee replacement prosthetic is a hinge-type articulation, consisting of the rounded condyles of the lower part of the thigh bone (the femur), flexing and extending along the flat surface of the upper part of the shin bone (the tibia). The femoral component, which re-surfaces the arthritic femoral condyles (similar to capping a tooth) is made of a very durable, polished metal, a cobalt-chrome alloy. This implant is cemented into the femur using high-viscosity bone cement.
On the tibial side, the bearing surface is made of a highly cross-linked polyethylene liner and is locked into the tibial baseplate, which is made of titanium alloy. The tibial baseplate is cemented into the tibia using the same high-viscosity bone cement. Thus, the final bearing surface is metal-on-polyethylene.