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Partial Knee replacement


Unicompartmental Knee Replacement (UKR) simply means that only a part of the knee joint is replaced through a smaller incision than would normally be used for a total knee replacement.

UKRs have been performed since the early 1970′s with mixed success. Over the last 25 years implant design, instrumentation and surgical technique have improved markedly making it a successful procedure for unicompartmental arthritis. UKR is performed through a smaller incision and therefore is not as traumatic to the knee making recovery quicker. Recently we have commenced Robotically Assisted UKR with the ability to implant components more accurately, which should lead to a decrease in failures.

Am I a candidate for UKR?

This procedure is suitable for patients that have pain and reduction of activities as a result of localised arthritis in their knee, which has not responded to non-operative treatment. The knee has three compartments (medial, lateral and the patella or knee cap). When your symptoms are very localized i.e. pain is felt just on the inside of your knee, and your X-rays show only arthritis in one compartment you may be a candidate for UKR.


The diagnosis of osteoarthritis is made on history, physical examination & X-rays. We will often organise either an MRI or a CT arthrogram to determine if there is wear in the other compartments of your knee. This is to make sure that your knee is unlikely to develop pain in other part of the joint in the foreseeable future.

There is no blood test to diagnose Osteoarthritis (wear & tear arthritis).

Advantages & Disadvantages

The decision to proceed with UKR surgery is a cooperative one between you, your surgeon, family and your local doctor.

The benefits following surgery are relief of symptoms of arthritis. These include:

  • Severe pain that limits your everyday activities including walking, shopping, visiting friends, getting in and out of chair, gardening, etc.
  • Pain waking you at night

Prior to surgery you will usually have tried some conservative treatments such as simple analgesics, weight loss, anti-inflammatory medications, modification of your activities, and or physical therapy (exercise).

Advantages compared to TKR

Advantages of a UKR include:

  • Smaller operation
  • Smaller incision
  • Not as much bone removed
  • Shorter hospital stay
  • Shorter recovery period
  • Better movement in the knee
  • Feels more like a normal knee
  • Less need for physiotherapy
  • Able to be more active than after a total knee replacement


UKR has previously been associated with higher failure rates than total knee replacement. It is this reason that has led our surgeons to pursue Robotic assisted UKR in an effort to reduce these failure rates with very encouraging early results.

Who is not suitable for UKR?

  • Patients with arthritis affecting more than one compartment
  • Patients with severe angular deformity
  • Patients with inflammatory arthritis e.g.: rheumatoid arthritis
  • Patients with an unstable knee
  • Patients who have had a previous osteotomy
  • Patients who are involved in heavy work or contact sports


  • Your surgeon will send you for routine blood tests and any other investigations required prior to your surgery.
  • You may be asked to undertake a general medical check-up with a physician.
  • You should have any other medical, surgical or dental problems attended to prior to your surgery.
  • Make arrangements for help around the house prior to surgery.
  • Cease aspirin or anti-inflammatory medications 7-10 days (as directed) prior to surgery as they can cause bleeding.
  • Cease any naturopathic or herbal medications 10 days before surgery.
  • Stop smoking as long as possible prior to surgery.

Day of Surgery

  • You will be admitted to the hospital usually on the day of your surgery.
  • Further tests may be required on admission.
  • You will meet the nurses and answer some questions for the hospital records.
  • You will meet your Anesthetist, who will ask you a few more questions (as they will have contacted you prior to the procedure).
  • You will be given hospital clothes to change into and have a shower prior to surgery.
  • The operation site will be shaved and cleaned.
  • Approximately 30 minutes prior to surgery, you will be transferred to the operating room.

Surgical Procedure

  • Surgery is performed under sterile conditions in the operating room under spinal or general anesthesia. You will be lying on your back. Surgery will take approximately two hours.
  • The Patient is positioned on the operating table and the leg prepped and draped.
  • A tourniquet is applied to the upper thigh and the leg is prepared for the surgery with a sterilizing solution.
  • An incision around 7cm is made to expose the knee joint. Each knee is individual and knee replacements take this into account by having different sizes for your knee.
  • The bone ends of the femur and tibia are prepared using a saw or a burr.
  • Trial components are then inserted to make sure they fit properly.
  • The real components (Femoral & Tibial) are then put into place with or without cement.
  • The knee is then carefully closed, and the knee dressed and bandaged.

Post-operation Course

When you wake, you will be in the recovery room with intravenous drips in your arm, a tube (catheter) in your bladder and a number of other monitors to check your vital observations.

Once stable, you will be taken to the ward. You will be able to stand within hours and beginning to walk within 24 hours. Your rehabilitation and mobilisation will be supervised by the physiotherapist and the nursing staff.

To avoid lung congestion, it is important to breathe deeply and cough up any phlegm you may have.

Your Orthopaedic Surgeon will use one or more measures to minimize blood clots in you legs, such as inflatable leg coverings, stockings and injections into your abdomen to thin the blood to prevent blood clots (DVT).

A lot of the long term results of knee replacements depend on how much work you put into it following your operation.

Usually you will remain in the hospital for 2 days. You are likely to need physical therapy on your knee following surgery.

You will be discharged on a walker or crutches and usually progress off the crutched within weeks.

Your sutures are sometimes dissolvable but if not, are removed at approx. 10 days.

Bending your knee is variable, but by 2 days it should bend to 90 degrees. The goal is to obtain over 115 degrees of movement.

Once the wound is healed, you may shower. You can drive at about 6 weeks, once you have regained control of your leg. You should be walking reasonably comfortably by 6 weeks.

More physical activities, such as sports previously discussed may take 3 months to be able to do comfortably.

When you go home you need to take special precautions around the house to make sure it is safe. You may need rails in your bathroom or to modify your sleeping arrangements especially if they are up a lot of stairs.

You will usually have a routine check up with your surgeon, who will assess your progress. You should continue to see your surgeon for the rest of your life to check your knee and take X-rays. This is important as sometimes your knee can feel excellent, but there can be a problem only recognized on X-ray.

If you have any unexplained pain, swelling, or redness or if you feel generally poor, you should see your doctor as soon as possible.

Risks and Complications

As with any major surgery, there are potential risks involved. The decision to proceed with the surgery is made because the advantages of surgery outweigh the potential disadvantages.

It is important that you are informed of these risks before the surgery takes place.  Complications can be medical (general) or local complications specific to the Knee.

Medical complications include those of the anesthetic and your general well being. Almost any medical condition can occur so this list is not complete.

Complications include:

  • Allergic reactions to medications
  • Blood loss requiring transfusion with its low risk of disease transmission
  • Heart attacks, strokes, kidney failure, pneumonia, bladder infections
  • Complications from nerve blocks such as infection or nerve damage
  • Serious medical problems can lead to ongoing health concerns, prolonged hospitalization or rarely death

Local Complications


Infection can occur with any operation. In the hip this can be superficial or deep. Infection rates are approximately 1%. If it occurs, it can be treated with antibiotics but may require further surgery. Very rarely your hip may need to be removed to eradicate infection.

Blood Clots (Deep Venous Thrombosis)

These can form in the calf muscles and can travel to the lung (Pulmonary embolism). These can occasionally be serious and even life threatening. If you get calf pain or shortness of breath at any stage, you should notify your surgeon.

Stiffness in the Knee

Ideally, your knee should bend beyond 115 degrees but on occasion, may not bend as well as expected. Sometimes manipulations are required. This means going to the operating room where the knee is bent for you while under anesthetic.


The plastic liner eventually wears out over time, usually over 10 to 15 years, and may need to be changed. Alternatively the remainder of your own knee may wear out requiring revision to a Total Knee Replacement.

Fractures or Breaks in the Bone

Fractures or breaks can occur during surgery or afterwards if you fall. To repair these, you may require surgery.

Wound Irritation or Breakdown

The operation will always cut some skin nerves, so you will inevitably have some numbness around the wound. This does not affect the function of your joint. You can also get some aching around the scar. Vitamin E cream and massaging can help reduce this.

Occasionally, you can get reactions to the sutures or a wound breakdown that may require antibiotics or rarely, further surgery.

Cosmetic Appearance

The knee may look different than it was because it is put into the correct alignment to allow proper function.

Leg length Inequality

Your leg will be restored to it’s original length as the deformity caused by wearing of the knee has been corrected.

Ligament Injuries

There are a number of ligaments surrounding the knee. These ligaments can be torn during surgery or break or stretch out any time afterwards. Surgery may be required to correct this problem. This problem is minimised with robotic assistance.

Damage to Nerves and Blood Vessels

Rarely these can be damaged at the time of surgery. If recognized they are repaired but a second operation may be required. Nerve damage can cause a loss of feeling or movement below the knee and can be permanent.

Discuss your concerns thoroughly with your Orthopaedic Surgeon prior to surgery.


Surgery is not a pleasant prospect for anyone, but for some people with arthritis, it could mean the difference between leading a normal life or putting up with a debilitating condition. Surgery can be regarded as part of your treatment plan it may help to restore function to your damaged joints as well as relieve pain.

Surgery is only offered once non-operative treatment has failed. It is an important decision to make and ultimately it is an informed decision between you, your surgeon, family and GP.

Although most people are extremely happy with their new knee, complications can occur and you must be aware of these prior to making a decision. If you are undecided, it is best to wait until you are sure this is the procedure for you.