The knee prosthesis is the artificial substitute for the knee joint. The knee prosthesis initially had a hinge shape, currently have a shape similar to that of the human knee; They are usually composed of two components: the femoral, which has a rounded shape imitating the femoral condyles; the tibial: which has a flat shape imitating the shape of the tibial plate. By having a shape similar to the original knee also the movement is similar to this.
The replacement of the knee joint by a prosthesis is usually done when the deterioration of the cartilage (osteoarthritis) is such that it is impossible to carry out a normal life interfering with the ability to walk despite using appropriate medication.
The surgery that is performed to implant a knee prosthesis, begins by partially or totally removing the damaged surface of the joint. The artificial components will anchor to healthy bone in the area where the diseased cartilage has been removed.
Components of the knee prosthesis:
Femoral component: This part is the one that is anchored to the femur. It has the same shape as the patient’s femur. In the case of total prostheses, which replace the entire knee joint, the femoral component has a bilobed shape (two lobes). In case of being partial prostheses, that is to say those that substitute only a small damaged area, it will have the shape of a femoral condyle (a lobe). This component is usually metallic.
Tibial component: This component is the one that is anchored in the tibia. It has a flat shape with a slight concavity. In the case of total prostheses this component has 2 concavities to house the 2 prominences of the femoral component. When the prosthesis is parcel, it will only be a concavity. This component is anchored to the tibia by means of a metallic module, to this the dish is attached, which is usually made of high density polyethylene, this polyethylene dish is the one that will be in contact with the metal surface of the femoral component.
Patellar or patellar component: The patella can also be damaged by osteoarthritis and in certain cases it is necessary to change its surface. For this, the damaged surface is removed and the patellar component is inserted, which will have a metallic side on one side, which is the one that remains in contact with the bone of the label; while in the opposite slope presented polyethylene with a very smooth surface (in order to favor the slip) that would contact the femoral component. The implantation of this component is not obligatory, it will depend on the degree of deterioration of the label as well as the preferences of the surgeon.
When is the best time to implant a knee prosthesis?
As for any other prosthesis, we understand that the later the better. We have this opinion because the prosthesis is subject to movement and therefore to wear, so that over time these prostheses must be replaced; replacement surgery is a much more aggressive surgery and with worse results than primary, therefore as far as possible we want to avoid it. The later it is implanted the lower the chances of requiring a replacement in the future.
In addition once implanted a prosthesis there is no return back to the previous situation; we must be completely sure that the pain can not be alleviated with conservative measures (medication and weight loss) and that it is not a temporary pain.
We should not be in a hurry when deciding to implant a prosthesis.
How long does a knee prosthesis last?
Being inert compounds and being in constant movement the prosthesis wear out. The duration is variable and will depend on many factors, such as the weight of the patient, the use given, the axes of the knee, the quality of the bone where it is anchored, etc. In general, it can be said that the duration fluctuates from 10 to 15 years as an average term.