Unicompartmental Knee Replacement
The knee joint is divided into three compartments. The medial compartment, the lateral compartment and the patellofemoral compartment. A unicompartmental (partial) knee replacement is a prosthesis which replaces only one compartment of the knee. This is usually the medial compartment.
In a standard total knee replacement all three compartments are generally replaced. In a number of patients the arthritic process only affects the medial or lateral compartment. Provided certain conditions are fulfilled it may be more appropriate to undertake a partial knee replacement instead. This involves resurfacing the diseased medial or lateral compartment with metal components and placing a wear resistant, plastic bearing between the metal components
What are the advantages of unicompartmental (partial) knee replacement?
Because the partial knee replacement requires a smaller approach to the knee and removes less tissue there are a number of advantages. These include less pain after surgery and a more rapid recovery. Because this procedure preserves more of the natural joint and ligaments this results in a more natural motion (compared to total knee replacement) and potentially better function. Studies have demonstrated that patients who have undergone partial knee replacement surgery tend to walk with a greater stride length, find ascending and descending stairs easier and have better range of movement of the knee joint compared to patients with total knee replacement. Studies have also demonstrated fewer medical complications, reduced risk of blood transfusion and lower mortality. It should be noted however that outcomes from total knee replacements are still very good with low complication rates.
What are the risks of Partial Knee Replacement Surgery?
The risks of this procedure are small and are similar but lower to those of a total knee replacement. These include infection, thromboembolism, stiffness, injury to nerves or blood vessels, ligament damage, fracture and loosening of the prosthesis. In addition there is a small risk of bearing dislocation in certain prostheses. All of these risks are small but if they were to occur it may be necessary to revise the prosthesis to a standard total knee replacement.
What sort of knee replacement would be best for me?
In order for a partial knee prosthesis to be used successfully a number of criteria need to be fulfilled. These include good preservation of the other compartments of the knee, minimal fixed deformity of the joint, intact ligaments and the absence of an inflammatory type of arthritis. It is also preferable that the arthritic pain is well localised to either the medial (inner) or lateral (outer) aspect of the knee joint. If these criteria are not fulfilled then a standard total knee replacement would be the preferred option. Only about 20-30% of patients undergoing knee replacement surgery are regarded as suitable for a partial replacement.
Your surgeon will be able to guide you as to which type of knee replacement would be most suitable for your individual circumstances.