The surgery involves removing a very small thickness of damaged bone from the inside part of the knee. Much less bone is removed than in a total knee replacement and only from one side of the knee. The partial knee replacement fits inside this prepared space and is fixed to the bone with cement.
The operation takes about an hour and involves an 8cm incision on the medial (inner) side of the kneecap. This small incision does not involve cutting any muscle or tendons (as with a total knee replacement), thus enabling quicker recovery from surgery.
The unicompartmental knee replacement comes in three parts. The femoral component is made of metal, is curved and highly polished. The tibial component is made of the same metal and has a flat upper surface. A plastic component, which is curved on the top and flat on the underside, sits on the flat tibial surface and can slide backwards and forwards. This mimics the meniscal cartilage in the normal knee. The upper part of this plastic insert articulates with the femoral component. This type of knee replacement is called a meniscal bearing and has the advantage of sharing the load through the knee over a large surface area, which helps to reduce wear and hence make the knee replacement last longer.