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Knee replacement (partial) surgery
The knee joint includes the patella, the lower end of the femur and the upper tibia, all are enclosed within the same sleeve of synovial membrane and supported by the surrounding ligaments and muscles. Functionally there are three separate compartments: the patellofemoral joint between the deep surface of the patella and the front of the femur; the medial compartment between the medial femoral condyle and the medial tibial plateau on the inner aspect of the knee; and the lateral compartment between the lateral femoral condyle and the lateral tibial plateau on the outer aspect of the knee.
Osteoarthritis can affect one, two or all three of these joint compartments to a greater or lesser degree. As a result of this we can choose to replace just the affected part of the joint in about 50% of cases of osteoarthritis rather than the whole joint. The big advantage of this is that it is a smaller operation than a total knee replacement, with less blood loss and a shorter stay in hospital. It also results in a more normal feel to the knee and better overall function.
Partial replacements of just one compartment are called uni-compartmental knee replacements; two compartments – bi-compartmental knee replacements and three compartments – total knee replacements.
Resurfacing rather than replacement
The procedure of uni-compartmental or bi-compartmental knee replacement is more of a resurfacing procedure rather than a replacement, although the word replacement is still most commonly used. In effect a relatively thin layer of bone and cartilage is removed no thicker than 9 mm in most cases from the affected surfaces and replaced with a ceramic on metal surface with a plastic or high density polyethylene bearing. It is important to realise that during a UKR there is always the potential for the surgeon to have to switch to a total knee replacement for technical reasons if the knee is just not suitable for a partial knee procedure. Your surgeon will discuss this with you during consultation. Generally speaking partial knee replacements are not suitable for patients with inflammatory conditions arthritis such as rheumatoid arthritis.