Because of its anatomy, most of the weight is borne through the medial (inner) compartment of the knee. As a result, the articular cartilage on the inner side and the medial meniscus tend to wear more quickly than on the lateral side. Consequently, the knee tends to become ‘bowed’ and even more weight is borne through the medial compartment.

In time it is likely that most patients will have progression of their arthritis to the other compartments – the lateral and patello-femoral (kneecap joint). However patients who have arthritis confined to the medial compartment, and whose symptoms are uncontrolled with non-operative treatment, may be suitable for an operation to replace only this part of the knee. Replacement of only one compartment of the knee is termed a unicompartmental knee replacement.

In some cases, arthritis is confined to either the patello-femoral (kneecap) or lateral part of the knee. Unicompartmental replacement of these parts of the knee is also possible but is performed far less frequently than replacement of the medial compartment. The results are less predictable.

About 2000 unicompartmental knee replacements are performed in the UK each year. The most commonly used is the ‘Oxford Uni’ made by Biomet. It is designed to be used with cement, and consists of metal femoral and tibial components with a mobile plastic bearing in between.

Click here to view basic knee anatomy which provides a helpful reference for these pages.


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