Revision of a plastic during a knee replacement surgery is rarely done. The reason would be if the knee is loose or has loosened after a knee replacement and the surgeon wants a thicker plastic between the knee joint to provide additional stability. Another reason would be if the primary knee was posterior cruciate ligament (PCL) sparing knee joint, meaning that one of the ligaments in the knee joint, the posterior cruciate ligament, was left behind in the knee joint and has given way. Under this circumstance, the plastic, which was PCL sparing, is removed and can be replaced with the cruciate substituting plastic.
However, in all likelihood, if the PCL sparing knee was performed, the femoral component does not accept the plastic that is there, which is cruciate substituting, and therefore the femoral as well as the tibial component, has to be revised. To summarize, the most common reason for changing only the plastic, is if the knee is loose and the reason for the loosening is the smaller size of the plastic, or if the surgeon feels that a larger “stabilizing post” with a thicker poly will cure the reason for unstable knee joint.