A partial knee replacement observes the same principles as total knee replacement, but is done to replace the worn out part of the knee when only either the inner, or the outer or the patellofemoral area of the knee is arthritic.
In order to have a partial knee replacement the patient has to have a reasonably healthy knee in other respects, although, the other parts of the knee do not have to be pristine by any means. It is preferable to have a stable knee and, therefore, more surgeons would want the anterior cruciate ligament to be intact. The perceived advantage of a partial knee replacement is that the level of function is demonstrably superior (numerous walking studies and functional studies have demonstrated this) compared to a total knee replacement, particularly in activities such as fast walking, walking down slopes and more vigorous sports, such as squash and skiing.
However, the majority of orthopaedic surgeons in the UK do not perform partial knee replacements, as they regard them as somewhat unpredictable and looking at evidence in the National Joint Registry, which shows that partial knee replacements have a higher redo (revision) rate than total knee replacement.
This data should not be taken at face value, however, as there is an inherent bias towards redo when a partial knee replacement is performed, as the treating surgeon always has the option of redo to a total knee replacement, which is not the case, if a total knee replacement is done in the first place. The main disadvantage of partial knee replacement is if the rest of the knee becomes arthritic around it (this is known as disease progression).
If the surgeon wants to do a partial knee replacement he or she should satisfy themselves that the other parts of the knee are in reasonable health, and the knee is stable with a good range of motion, and that the aspirations of the patient and the level function required justifies the choice of partial knee replacement. In my experience a partial knee replacement offers an extremely satisfying outcome and certainly a good partial knee replacement offers a better level of function than a good total knee replacement.
In my practice 25% of the patients who come to see me with knee arthritis are suitable for partial knee replacement. Other surgeons vary in their estimations from between 5% up to 50%.
Patients for partial knee replacement have the operation done under general or spinal anaesthetic. Generally speaking, they are in hospital for an average of two nights, but can be in up to four. They mobilise as soon as possible and use crutches only for pain control. Generally speaking, they are able to drive within two weeks and walk normally around the two week mark, but again, like total knee replacement, it takes some months to get back to a completely normal level of activity.
