Up to three bone surfaces may be replaced in a total knee replacement:
· The lower ends of the femur. The metal femoral component curves around the end of the femur (thighbone).
It is grooved so the kneecap can move up and down smoothly against the bone as the knee bends and straightens.
· The top surface of the tibia. The tibial component is typically a flat metal platform with a cushion of strong,
durable plastic, called polyethylene. Some designs do not have the metal portion and attach the polyethylene
directly to the bone. For additional stability, the metal portion of the component may have a stem that inserts
into the center of the tibia bone.
· The back surface of the patella. The patellar component is a dome-shaped piece of polyethylene that duplicates
the shape of the patella (kneecap).
Components are designed so that metal always adjoins with plastic, which provides smooth movement and results
in minimal wear. The material of the implant must be biocompatible, in order to be staying in human body without
a rejection response. They must be able to duplicate the knee structures which they are designed to replace.
And they also need to retain their strength and shape for a long time. So for the metal parts of the implant, titanium
or cobalt-chromium based alloys are always chosen, and the plastic parts are normally made of ultra high molecular
weight polyethylene,because they have suitable material properties.