Operation of a knee prosthesis | Material of a knee prosthesis

Operation of a knee prosthesis

The aim of implanting a knee prosthesis is to replace the worn cartilaginous part of the knee joint with a procedure that removes as little of the existing bone tissue as possible. The extent of the operation therefore depends on the extent of the damage to the knee joint. If possible, the patient’s own knee ligaments should also be preserved.

Depending on the wear and tear of the joint, three different prostheses are available.The unilateral surface replacement, also called unicondylar sled prosthesis, in which the surface of one of the two femoral rolls (condyles) is replaced. Or the complete surface replacement, also called total knee endoprosthesis (knee TEP) in medical terminology. A third technique is the complete surface replacement with an axially guided pedicle knee prosthesis.

The more the patient’s ligamentous apparatus is affected by the operation, the more of the stresses and strains that occur in daily life must later be taken over by the prosthesis. The classification of the prostheses is therefore also based on the so-called degree of coupling. The higher the degree of coupling, the more immobile the knee joint is after the operation.

The unicondylar sled prosthesis is usually an uncoupled prosthesis, the knee TEP is an uncoupled or partially coupled prosthesis and the axis-guided knee prosthesis is a fully coupled prosthesis. Which type of prosthesis is used in a patient depends on the patient’s age, mobility and state of health as well as the degree of wear of the joint and the condition of bones and ligaments. With the unicondylar sled prosthesis, only one of the two femoral rolls is provided with a surface replacement.

This is the smallest and lightest procedure. This technique can only be considered if only one of the two femoral rolls is worn out, the rest of the knee joint is functioning properly and the ligamentous apparatus is intact. Therefore, the knee total endoprosthesis (knee TEP) is used most frequently.

In this procedure, the knee joint is completely removed and its components replaced by artificial elements. The knee TEP is an artificial hinge joint, and as such can fulfill all the tasks of the original joint and allows stability and a secure stand with the leg stretched. The replacement of the diseased knee joint is performed under general anesthesia.

The surgeon opens up the affected knee while preserving healthy structures such as muscles and ligaments and obtains an overview of the extent of the joint damage. Depending on the extent of the damage, the surgeon decides which type of knee prosthesis should be used. In surface replacement, the worn joint surfaces are completely replaced by artificial surfaces made of a robust and lubricated metal alloy.

These newly inserted elements are held in place by wedges that are anchored in the femur and tibia respectively. In the axially guided knee TEP, the original joint surfaces are also replaced by artificial materials. In the axially guided knee TEP, the anchoring in the bone is deeper than in the pure surface replacement.

In addition, the components inserted in the thigh and tibia are coupled at the level of the kneecap to prevent lateral slippage. This type of prosthesis is used when the originally existing ligamentous apparatus is already severely damaged and could not provide support for an uncoupled surface replacement.