The knee is one of the main joints of the human body .
In fact, situated between the distal portion of the femur (superiorly) and the proximal portion of the tibia (inferiorly), it allows the movement of the legs (together with the hip) and absorbs most of the weight exercised by the trunk.
Like any joint, the knee is also made up of ligaments, tendons and cartilage, each of which has a fundamental function that cannot be ignored.
When a knee is a victim of severe deterioration (for example due to osteoarthritis, rheumatoid arthritis, haemophilia, etc.), implantation of a prosthesis may become necessary.
The implantation of a modern knee prosthesis consists in applying artificial elements between the tibia and the femur, capable of replacing the original articulation and alleviating the problems caused by serious damage.
The current total-type knee prostheses consist essentially of four parts :
- A curved plate, designed to cover the distal portion of the femur . It is the upper part of the prosthetic element.
The material with which it is usually made is of the metal type: titanium or an alloy between cobalt and chromium.
- A flat plate, designed to cover the proximal portion of the tibia . It is the lower part of the prosthesis.
The material from which it is generally constituted is of the metallic type: as previously, titanium or cobalt-chromium alloy.
- A spacer element, or insert, designed to interpose between the curved plate and the flat plate . It plays the same role as articular cartilage, so it prevents rubbing between the two plates.
The material of construction is a particular plastic, called polyethylene.
- An artificial kneecap, made of polyethylene.
Each component of the prosthesis weighs between 420 and 570 grams (15-20 ounces).
CRITERIA FOR THE CHOICE OF MATERIALS
The materials with which knee implants are made today are chosen based on the following criteria:- First of all they must be biocompatible, that is they must not be harmful to the health of the organism or even give rise to an exaggerated reaction on the part of the immune system.
- Secondly, they must be able to " replicate " the original joint elements in the best possible way. Therefore, they must be strong enough to withstand the weight and stress exerted by the upper part of the human body.
- Finally, they must be able to keep their shape and last a long time .
