Partial knee replacement, or as it is sometimes referred to, Unicompartmental knee replacement is based on the idea that not all the knee wears out at once. The natural knee can be thought of as having three compartments:

1) Patello femoral (behind the knee cap)

2) Medial

3) Lateral

Most commonly, the medial compartment becomes symptomatic first, but the rest of the knee may be in very good health. While it may be technically easier to simply do a total knee replacement, a partial knee replacement is a smaller operation with a faster recovery and gives a much more "normal" or "natural" feeling knee as all of the tendons and ligaments remain. This is on top of the benefits of knee replacement such as pain relief, improved mobility and general increase in the quality of life.

The disadvantages of partial knee replacement compared with total knee replacement are:

1) Technically more difficult to do

2) Survival of the replacement can be less than a total knee replacement, as a high demand patient will wear it out, or the disease process could progress to the remaining compartments of the knee due to natural progression.

3) Some knees will be too badly damaged to allow a partial knee replacement

A partial knee replacement that does wear out can relatively easily be revised (changed) to a total knee replacement.

The picture above shows a Bicompartmental knee replacement. It is made up of a patellofemoral replacement and a medial compartment uni compartmental replacement. The image is of the Sigma System by Depuy.