Total Knee Replacement
A knee replacement involves removing a thin layer of bone from the damaged surface of the femur (thigh bone), using special instruments which remove the correct thickness of bone. The removed bone is then replaced by a thin layer of metal, approximately the same thickness as the bone which was removed.
In a similar fashion the upper end of the tibia (shin bone) is removed and is replaced with a wafer of plastic. The back part of the knee cap (patella) may also be resurfaced with a piece of plastic.
In most cases, the three parts are attached to the bone by means of a bone cement. When this cement is first mixed it develops a dough-like consistency. This dough is pressed into the bone and the parts of the Prosthesis are pressed into the dough. The cement then hardens over 10 to 15 minutes into a plastic-like consistency.
After the knee has been replaced, the metal "cap" covering the end of the femur rubs against the plastic covering on the end of the tibia, preventing bone from rubbing on bone and giving relief from pain. The plastic is high density polyethylene a material which has a very low wear-rate and a very low frictional resistance when rubbing against the highly polished metal surface.