When one considers the human knee joint from the point of view of joint replacement surgery, there are a number of components to think of. These are: the lower end of the thigh bone (femur), the top end of the shin bone (tibia), the knee cap (patella) and the posterior cruciate ligament. All surgeons replace the lower end of the femur and the top end of the tibia. About half the surgeons remove the posterior cruciate ligament and another half or so do not. Similiarly, about half do not put a new piece on the back of the knee cap and the other half do. This does sound odd, but there appear to be subtle pros and cons of both these latter options. It is Mr. Trakru's standard practice to put a new piece on the back of the knee cap and to remove the posterior cruciate ligament during knee replacement surgery.
The precise choice of implant is made by the specialist taking into account the damage caused to the knee from the arthritic process, the specialists' own experience and training and whether the knee replacement is being done for the first time or is a second time replacement for a previously carried out but failed artifical knee operation. Whatever design is chosen, it is very likely to have a bearing made of metal which is placed on the lower end of the thigh bone (the femoral component) and a metal plate on top of the leg bone (the tibial component). A bearing made of special plastic (UHMWPE or Ultra High Molecular Weight Poly Ethylene) is placed in between the femoral and the tibial component so that when the knee bends, it is the femoral component which moves over the polyethylene. In common with many surgeons, Mr. Trakru uses a system where both these metal components are fixed to the skeleton with bone cement. He also implants a new surface on the back of the knee cap. While newer implants using other materials such as ceramic are available in the market, the long term results with these are not as well known as with the other older metal types.
The femoral component: This component is used to replace the lower end of the thigh bone and in fact looks very much like the lower end of that bone. All the systems in the market have a number of different sizes available and the final choice of implant size is made during the operation.
The tibial component: The tibial component has a flat plate with a fairly substantial peg on its undersurface. It is cemented into a specially prepared cavity within the leg bone. The component also has a capture mechanism to retain the polyethylene bearing surface that is slotted onto its top surface. The tibial implant has the facility to take polyethylene inserts of various thickness according to the requirements of the individual patient.