Knee Procedures
Unicompartmental Knee Replacement

General Information

If you have arthritis in your knee, your surgeon may suggest this operation.

About Knee Arthritis

Your knee joint is essentially made up of three compartments:

  • Your kneecap (patellofemoral compartment)
  • The inner aspect of your knee (medial compartment)
  • The outer aspect of your knee (lateral compartment)

Any or all of these can be affected by arthritis. The medial compartment between the tibia and the femur is by far the most commonly affected by arthritis.

What is a Unicompartmental Knee Replacement?

A Unicompartmental Knee Replacement (commonly known as a “Uni-knee”) is performed when arthritis is confined to only one compartment of the knee. The arthritis is surgically removed and replaced with a prosthesis (artificial knee). Unfortunately, not all patients are suitable for this operation. Your surgeon will discuss your specific case with you.

Is it a smaller operation that a total knee replacement?

Yes. Having a UKR is a much less surgically invasive procedure than a total knee replacement. The operation time is shorter, less time is spent in hospital, rehabilitation is more rapid and the knee feels more “natural” compared to a total knee replacement.

Provided that you are a suitable candidate for having a Uni-knee, excellent long term results, measured by improved function and reduced pain, can be expected from this operation.

When is a Unicompartmental Knee Replacement helpful?

This operation is not suitable for all arthritis patients. Your surgeon will assess a range of factors such as: where and how severe your arthritis is, how much “wear and tear” your knee joint will be subject to over time, the degree of knee deformity and the amount of stiffness in your knee.

The most important reason for surgery is pain that is interfering with your quality of life and that you cannot adequately control by other means (medication, injections, physiotherapy, activity modifications etc). This is a very individual decision and depends on your social requirements and activity demands.


What happens after you go home?

Your rehabilitation will continue after you leave hospital to initially maintain and then improve on what you have already achieved. This will take the form of a home exercise program and sessions with your physio over about 3-6 months.

An appointment will be made to see your surgeon at 2 weeks after your operation and then again at 6 weeks. The goals of your knee replacement surgery are to be walking independently, be able to bend your knee to 100-120 degrees and be pain free.

Things to do before your operation

Although less invasive than a Total Knee Replacement, undergoing a unicompartmental knee replacement is still a major operation. You will require specific tests (blood tests, ECG and other x-rays) and likely visits to other medical specialists to ensure you are in the best possible condition prior to undergoing surgery.

If you have a pre existing condition (such as previous heart disease) you will need to be given the “all clear” by your treating physician prior to surgery. In addition, your anaesthetist will explain to you the various options with regards to anaesthetic during the operation and the most suitable post operative pain relief for your situation.

What happens on the day of your operation?

You will be admitted into hospital usually on the day of your surgery. Your surgeon will visit you to answer any other questions you may have regarding the surgery. He will also mark the affected knee with an ink pen.

On the day of the operation, your knee to be operated on will be painted with an antiseptic solution and wrapped in a sterile sheet prior to entering the operating theatre

After your anaesthetic has been administered, a tight band (tourniquet) will be applied to your upper thigh and your leg will be re-painted with antiseptic solution. A routine draping will be performed with sterile sheets to allow exposure only of the knee.

A vertical incision (approx. 10 to 12 cm) is made on the front of your knee to allow access to the knee joint itself. The arthritic areas of your affected knee joint compartment are removed and the bones are fashioned to allow placement of the knee prosthesis (comprising a metal upper (femoral) and lower (tibial) component). Bone cement is used to help stabilize the prosthesis to the bone. A plastic (polyethylene) insert is placed on the lower tibial component and acts as an articulating shock absorbing surface.

Before completion of the operation, the knee is checked for stability, balance, alignment and degree of motion. Often, a small drain will be left in the knee for 24 hours after the surgery to remove unwanted blood from the knee. Dissolving stitches are used to close the wound and skin incision, and the knee is then wrapped in a well-padded sterile bandage.

After your operation

You will wake up in the recovery ward where you will be closely monitored until you are ready to return to your ward. Here you will continue to be observed until you are fully awake.

Depending on how you are feeling, you may start walking on the same day as your surgery under the supervision of a physiotherapist. Your physiotherapist will also give you breathing exercises for your chest as well as exercises for your leg that can be performed whilst in bed. An x-ray of your knee will be taken the day after surgery to confirm optimal placement of the prosthesis.

Blood thinning medications will be administered daily to reduce the risk of blood clots (DVT) forming in your legs. In addition you will be given special stockings (TEDS) to wear on both of your legs. For the first 24 hours after the operation an inflatable sleeve will intermittently compress your calves to prevent stagnation of blood flow. You will receive intravenous antibiotics for 24 hours after the operation to decrease the risk of infection.

The dressings will be changed 24 hours after the operation and your surgeon will check the wound. The wound may be swollen and may have areas of bruising. This is normal.

You will be under the daily supervision of a physiotherapist until you are discharged from hospital.

The aims of these visits are to optimise motion in the knee, help you walk normally, improve muscle strength around the knee and control knee swelling (please also see Total Knee Replacement Rehabilitation).

Once you are mobilising safely, have regained appropriate motion in the knee and your pain is controlled by oral pain medication you will be discharged home. Most patients remain in hospital for between 2 and 4 days.