(Also known as Unicondylar Knee Replacement)

What is a Unicondylar Knee Replacement?

Unicondylar Knee Replacement 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.

Unicondylar Knee Replacements 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 very successful procedure for unicompartmental arthritis. Recent advances allow us to perform this through a smaller incision and therefore is not as traumatic to the knee making recovery quicker.

Total Knee Replacement surgery replaces the ends of the femur (thigh bone) and tibia (shin bone) with plastic inserted between them and usually the patella (knee cap).

What may cause you to consider a partial knee replacement?

Arthritis – Arthritis is a general term used for where the joint surface (cartilage) wears out. The joint surface is covered by a smooth articular surface that allows pain free movement in the joint. When the articular cartilage wears out, the bone ends rub on one another and cause pain. There are numerous conditions that can cause arthritis and often the exact cause is never known. In general, but not always it affects people as they get older (Osteoarthritis).

Other causes may include:

  • Trauma – Break or fracture
  • Increased stress – Overuse, overweight, etc.
  • Infection
  • Connective tissue disorders
  • Inactive lifestyle –  Additional body weight puts extra force on which may lead to arthritis
  • Swelling – Rheumatoid arthritis
  • Bone spurs or excessive bone can also build up around the edges of the joint

The combinations of these factors may make your knee stiff and limit activities due to pain or fatigue.

Advantages and disadvantages of a partial knee replacement

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

The potential benefits following surgery are relief of symptoms of:

  • Severe pain that limits your everyday activities including walking, getting in and out of chair, gardening etc.
  • Pain waking you at night
  • Deformity- Bowleg or knock knees
  • Stiffness

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

Advantages of a partial knee replacement may include:

  • Smaller operation
  • Smaller incision
  • Not as much bone removed
  • Shorter hospital stay
  • Shorter recovery period
  • Blood transfusion rarely required
  • 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


The disadvantages of a partial knee replacement may include:

  • For unknown reasons it is not as successful as a total knee replacement
  • Not quite as reliable as a total knee replacement in taking away the majority of pain
  • Long term results not quite as good as total knee replacement

Are you suitable for a partial knee replacement?

Ideally you should be:

  • Over 50 years of age
  • In pain to the point that it restricts your mobility and lifestyle
  • Clinically diagnosed and confirmed on X-ray

Who is not suitable for a partial knee replacement?

If you have:

  • Arthritis affecting more than one component of your knee
  • Severe angular deformity in you knee
  • Inflammatory arthritis e.g.. rheumatoid arthritis
  • Unstable knee
  • Had a previous osteotomy
  • Involved in heavy work or contact sports


Your surgeon will send you for/to:

  • Routine blood tests and any other investigations required prior to your surgery
  • Undertake a general medical check-up with a physician
  • 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 10 days 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

On the day of your surgery

On the day of your surgery you will most likely:

  • Be admitted to the hospital
  • Sent for a further tests that may be required
  • Meet the nurses and answer some questions for the hospital records
  • Meet your Anesthetist, who will ask you a few questions
  • Be given hospital clothes to change into and have a shower prior to surgery
  • Have the operation site will be shaved and cleaned

Approximately 30 minutes prior to surgery, you will be transferred to the operating room

Partial Knee Replacement procedure

Each knee is individual and knee replacements take this into account by having different sizes for your knee. If there is more than the usual amount of bone loss sometimes extra pieces of metal or bone are added.

Surgery is performed under sterile conditions in the operating room under spinal or general anesthesia. You will be on your back and a tourniquet applied to your upper thigh to reduce blood loss.

Surgery will usually take approximately two hours and follow this procedure:

  • You will be 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 sterilising solution
  • An incision around 7cm is made to expose the knee joint
  • 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 drains usually inserted, and the knee dressed and bandaged.

Post-operative care

Soon after your operation

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. You will usually have a button to press for pain medication called a PCA machine (Patient Controlled Analgesia).

24 to 48 hours

Once stable, you will be taken to the ward. The post-op protocol is surgeon dependant, but in general your drain will come out at 24 hours and you will sit out of bed and start moving you knee and walking on it within a day or two of surgery. The dressing will be reduced usually on the 2nd post-op day to make movement easier. Your rehabilitation and mobilisation will be supervised by a physical therapist.

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 minimise blood clots in you legs, such as inflatable leg coverings, stockings and injections into your abdomen to thin the blood clots or DVT’s, which will be discussed in detail in the complications section.

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

After 3-5 days

Usually you will remain in the hospital for 3-5 days. Depending on your needs, you will then return home or proceed to a rehabilitation facility. You will need physical therapy on your knee following surgery. Your sutures are sometimes dissolvable but if not, are removed at approximately 10 days.

You will be discharged on a walker or crutches and usually progress to a cane at six weeks.

After 6 weeks

  • You should be able to bend your knee to 90 degrees. The goal is 110-115 degrees of movement
  • You may be able to drive, once you have regained control of your leg
  • You should have a check up with your surgeon
  • You should be walking reasonably comfortably.

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 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 recognised on X-ray.

You are always at risk of infections especially with any dental work or other surgical procedures where germs (Bacteria) can get into the blood stream and find their way to your knee.

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 may include:

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

Local complications

Infection – 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.

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.

Stiffness in the knee – Ideally, your knee should bend beyond 100 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.

Wear – The plastic liner eventually wears out over time, usually 10 to 15 years and may need to be changed.

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 – This is also due to the fact that a corrected knee is more straight and is unavoidable.

Dislocation – An extremely rare condition where the ends of the knee joint lose contact with each other or the plastic insert can lose contact with the tibia (shinbone) or the femur (thigh bone).

Knee problems – The knee cap can dislocate.  This means it moves out of place and it can break or loosen.

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.

Damage to nerves and blood vessels – Rarely these can be damaged at the time of surgery. If recognised 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 medical practitioner.

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.

Discussing any surgical option can be stressful. So if you have any any questions please do not hesitate to email me.
I will get back to you as soon as possible – Dr. David Love.