Unicompartmental Knee Replacement

A Unicompartmental Knee Replacement is a surgical procedure performed to treat chronic knee pain usually due to arthritis.
Knee arthritis is a condition where the smooth articular cartilage lining of the knee wears away. Eventually this exposes the underlying bone. Knee arthritis is associated with knee pain, stiffness and limitation of function.

Who should have a Unicompartmental Knee replacement?

A unicompartmental knee replacement is usually performed on someone over 60 with arthritis of the knee that is not able to be treated with other therapies. Most patients try some or all of physiotherapy, medication or injections into the knee prior to contemplating knee replacement. In patients less than 60 years of age unicompartmental knee replacement may still be performed if the symptoms are severe enough but there is increased risk.

Before Surgery

Prior to unicompartmentalknee replacement most patients will require a medical assessment by a physician. This allows detection and management of medical issues. The physician will usually be available at the time of the hospitalisation to help manage any medical issues.

Some blood tests will be required.

“Prehab” – Also prior to surgery “prehab” or preparation and exercise prior to surgery make a big difference to recovery. You will usually be seeing a physiotherapist a number of times before surgery to work on range of motion and strengthening. You will also learn how to use walking aids (usually crutches).

The pre-operative work makes recovering after surgery easier and faster.

The Surgery

Unicompartmentalknee replacement requires anincision on the front of the knee. Through this incision the arthritic surfaces of the knee are removed and the unicompartmental knee replacement inserted.

After The Surgery

The most important aspect of unicompartmentalknee replacement aftercare for the patient is early mobilisation. A physiotherapist will advise you on exercises to do in bed and also assist with beginning to walk again. Mobilisation after a unicompartmentalknee replacement is difficult especially at first and requires lots of hard work from the patient. The goals are safe walking, usually with an aid (crutches, walker) and good knee bend (at least 90 degrees prior to discharge home).

Most patients will achieve the ability to safely walk (with an aid) and good knee bend in a few days. For those who have difficulty a stay in a rehabilitation ward may be appropriate. Patients who prepare well usually have a faster recovery and can avoid the rehabilitation ward. Shorter stays in hospital lead to better results and less risk of complications.


The recovery time after unicompartmentalknee replacement is variable. Some patients have very fast recoveries and others take longer. Most patients will be able to manage crutches and be discharged home from hospital after a few days. Some patients will need longer. By 6 weeks most patients are mobilising well and beginning to return towards normal function, some however will still have significant pain and stiffness at that time. By 6 months 95% of people are doing well.

Physiotherapy before and after unicompartmentalknee replacement is very important. Physiotherapy helps with walking and pain relief and is crucially important with regards to bending the knee.

The Results

Unicompartmental knee replacement is an alternative to traditional knee replacement in the treatment of arthritis of the knee.

The proposed advantages of unicompartmental knee replacement are bone preservation, small surgical procedure and increased range of motion.

Initially there was a lot of enthusiasm for unicompartmental knee replacement and many surgeons were using it. Recent evidence from the National Joint Replacement Registry in Australia and sources in other parts of the world have demonstrated issues with unicompartmental knee replacement.

The failure rate of this procedure is higher than for traditional knee replacement methods. As such the number of surgeons performing unicompartmental knee replacement and the number of patients receiving unicompartmental knee replacement surgery have declined significantly.

Recently a robot has become available to assist in implanting the components of a unicompartmentknee into a good position. This is likely, in my view, to make a major difference in the results as poor position of implants is a major reason for failure. If improvement in positioning does indeed improve long term results then I expect unicompartment knee to become more commonly used.

Most people do well after unicompartmentalknee replacement, but certainly not all. There are a number of risks involved with the surgery, these will be explained in detail should you elect to proceed with a unicompartmental knee replacement.

In Australia the National Joint Replacement Registry collects data on all unicompartmentalknee replacements performed. Their data shows that after 10 years, 85% of knee replacements are still functioning. This means that 15 in 100 knees will require more surgery in the first 10 years. This usually involves revising the unicompartmental replacement to another implant. Reasons for this include infection, failure of implants, pain, etc.

A unicompartmentalknee replacement is not a normal knee and many patients feel that the knee feels different to a normal knee. Clicks and noises from unicompartmentalknee replacements are common and unless painful rarely a problem. Most patients have a patch of numbness near the knee, usually this causes no problems.

Unicompartmental knee replacements can be performed in patients under 60 years where the symptoms warrant. The failure rate of unicompartmentalknee replacement in patients under 55 is higher than the rate of failure in patients over 65.

Unicompartmental knee replacement is not appropriate in young patients who wish to perform heavy work.