Knee prosthesis types
Types of knee endoprostheses: There are different types of knee endoprostheses. It is not always necessary to replace the entire knee joint. Therefore, a distinction is made between a complete knee prosthesis and a partial joint replacement.
In both types of knee endoprostheses a distinction is also made between the extent to which the connection between the femoral and tibial components (femoral and tibial components) is guaranteed. A further distinction is made between different degrees of coupling of the knee prosthesis: In the early days of endoprosthetics, fully coupled prosthesis types (hinged prostheses) were predominantly used. However, since it was found out in scientific studies that partially coupled knee prostheses and non-coupled prostheses had a longer durability, fully coupled prosthesis models became less and less important.
These prosthesis models still have to be installed under unstable capsule – ligament conditions.
- Uncoupled knee prostheses
- Partially coupled knee prostheses/partially coupled knee prostheses
- Fully coupled knee prostheses, also called hinge prostheses
The above-mentioned classification of the prosthesis models therefore results in the following classification: To 1.) The uncoupled total endoprosthesis (joint surface replacement)This subgroup of the various types of knee prosthesis is most similar to normal knee mobility.
This is the case because, just like the normal human knee joint, both the femoral and tibial parts of the prosthesis type are not connected to each other like a hinge. In order to be able to fit this type of prosthesis, the anterior cruciate ligament does not have to be preserved; it is even surgically removed – if still present – before the prosthesis is implanted. This is necessary because the cruciate ligament, as the name suggests, crosses the knee joint.
The function of the cruciate ligament ́s is taken over by the artificial knee joint. In order to provide this type of prosthesis with maximum stability, the posterior cruciate ligament as well as the collateral ligaments should be fully functional. To 2).
The partially coupled knee endoprosthesisThis form of total knee endoprosthesis is mainly used in patients with weak ligament apparatus, thus usually in patients whose posterior cruciate ligament and/or collateral ligament is torn and/or damaged. The use of this knee prosthesis is often necessary, especially for rheumatism patients. In the course of the operation, a round, metallic stem is placed in the patient’s thigh from the tibia.
Care is taken to ensure that both extension and flexion as well as rotation are possible. To 3.) The fully coupled total endoprosthesisThey represent the first generation of all knee joint prostheses.
In contrast to the other knee joint prosthesis types described above, this form has the highest degree of coupling between the femoral and tibial components. One of the reasons for this is that these two components are connected by a rigid axle. This rigid axis functions like a kind of hinge joint and allows for flexion and extension, but rotation is not possible over this knee prosthesis.
A further disadvantage is its size and the associated weight, among other things. Due to the bulky nature of these prosthesis models, an excessive amount of bone substance must be “sacrificed”. Fully coupled total endoprostheses are usually fitted in the case of change operations, unstable joints, massive X-leg and O-leg.
When changing a prosthesis (prosthesis exchange operation), a so-called “revision model” must often be used, often the above-mentioned hinged prostheses are used. The anchoring of this type of prosthesis can be done either The bone cement is usually a fast hardening plastic. It is mixed during the knee prosthesis operation and hardens completely within a few minutes.
In case a prosthesis infection must be prevented, an antibiotic can be added to the mixture.
- Uncoupled total endoprosthesis
- Partially coupled total endoprosthesis
- Fully coupled total endoprosthesis
- Made of a metal runner for the thigh and
- Consists of a metal disc with plastic coating for the tibial head.
- Cemented or
- Uncemented.
- Complete knee joint replacement (=total prosthesis):With this knee prosthesis the complete joint surface of the head of the femur and the head of the tibia is replaced. Under certain circumstances a replacement of the back of the patella may also be necessary.
In the context of a complete knee joint replacement, a distinction is made between the:
- Uncoupled total endoprosthesis
- Partially coupled total endoprosthesis
- Fully coupled total endoprosthesis
- To 1) The uncoupled total endoprosthesis (joint surface replacement)This subgroup of the different types of knee prosthesis is most similar to normal knee mobility. This is because, just like the normal human knee joint, both the femoral and tibial parts of the prosthesis type are not connected to each other like a hinge. In order to be able to fit this type of prosthesis, the anterior cruciate ligament does not have to be preserved; it is even surgically removed – if still present – before the prosthesis is implanted.
This is necessary because the cruciate ligament, as the name suggests, crosses the knee joint. The function of the cruciate ligament ́s is taken over by the artificial knee joint. In order to provide this type of prosthesis with maximum stability, the posterior cruciate ligament as well as the collateral ligaments should be fully functional.
To 2). The partially coupled knee endoprosthesisThis form of total knee endoprosthesis is mainly used in patients with weak ligament apparatus, thus usually in patients whose posterior cruciate ligament and/or collateral ligament is torn and/or damaged. The use of this knee prosthesis is often necessary, especially for rheumatism patients.
In the course of the operation, a round, metallic stem is placed in the patient’s thigh from the tibia. Care is taken to ensure that both extension and flexion as well as rotation are possible. To 3.)
The fully coupled total endoprosthesisThey represent the first generation of all knee joint prostheses. In contrast to the other knee joint prosthesis types described above, this form has the highest degree of coupling between the femoral and tibial components. One of the reasons for this is that these two components are connected by a rigid axle.
This rigid axis functions like a kind of hinge joint and allows for flexion and extension, but rotation is not possible over this knee prosthesis. A further disadvantage is its size and the associated weight, among other things. Due to the bulky nature of these prosthesis models, an excessive amount of bone substance must be “sacrificed”.
Fully coupled total endoprostheses are usually fitted in the case of change operations, unstable joints, massive X-leg and O-leg. When changing a prosthesis (prosthesis exchange operation), a so-called “revision model” must often be used, often the above-mentioned hinged prostheses are used.
- Partial joint replacement (= sled prosthesis): If only the inner or outer section of the knee joint is affected by the destruction of the knee joint, it is not necessary to replace the entire knee joint. Depending on the individual state of the disease, today only the affected area is replaced with a so-called sled prosthesis, which consists of a metal skid for the thigh and a metal disc with plastic coating for the tibial head.
The anchoring of this type of prosthesis can be either cemented or uncemented. The bone cement is usually a fast hardening plastic. It is mixed during the knee prosthesis operation and hardens completely within a few minutes. In case a prosthesis infection must be prevented, an antibiotic can be added to the mixture.
- Made of a metal runner for the thigh and
- Consists of a metal disc with plastic coating for the tibial head.
- Cemented or
- Uncemented.
