A partial knee replacement is where half of the knee joint is removed and replaced with a metal and plastic prosthesis.
They are performed when there is damage to one side of the knee joint, usually from arthritis. They are sometimes known as a Uni Knee Replacement (UKR) or Unicompartmental Knee Arthroplasty.
Approximately half a million partial knee replacements are carried out each year in the US.
Here we will look at the indications for a UKR and how they different from total knee replacements. We will then go on to look at what surgery involves, the rehab and recovery process and common problems associated with the operation.
There are strict criteria that assess for the suitability of a uni knee replacement:
1) There can be no damage to the cartilage on the other side of the knee that isn’t being replaced
2) There must be full thickness loss of cartilage on the affected side
3) Both cruciate ligaments (ACL and PCL) should preferably be intact, however there are a few exceptions to this (see below)
4) Partial knee surgery is only suitable for osteoarthritis, not inflammatory arthritis (rheumatoid)
A person's age, weight and activity level do not usually impact suitability for the surgery.
In one third of cases, knee arthritis only affects one side of the knee. It is six times more likely to be the inner (medial) side rather than the outer (lateral) which is affected.
In the past, the whole knee had to be replaced, known as a total knee replacement (TKR) even if part of the knee joint was ok. But about thirty years ago partial knee replacement surgery was developed. It means it is possible to replace only one side of the knee joint meaning the unaffected part of the knee does not undergo unnecessary surgery and leads to a quicker and fuller recovery.
As a general rule, you need all your ligaments to be working properly to have a Uni Knee Replacement. However in 2003, the first combined partial knee replacement and ACL reconstruction was successfully performed in Oxford in the UK. I was the physio responsible for that patient’s rehab. It is always worth discussing with your surgeon what your options are.
People usually do really well after a partial knee replacement. Virtually all my clients who have had one absolutely rave about them. It is obviously a bit painful for a few weeks after the surgery but the post-operative pain is usually much less than the pain from arthritis and even that settles within a few weeks. People are always amazed how quickly they are up and about and get back to all their normal activities and more. Being able to walk, run and play sports again gives them a new lease of life.
If the surgeon thinks you are an appropriate candidate for partial knee surgery, have it. They work really well. You also have the reassurance of knowing that if something did go wrong (which hardly ever happens!) you still have the option of having a total knee replacement at a later date. It is much simpler to convert a partial knee to a total knee replacement than have a repeat TKR.
To find out more about partial knee replacement surgery, choose from the following sections.