Unicondylar Replacement

Unlike total knee replacement surgery, this less invasive procedure replaces only the damaged or arthritic parts of the knee.


The knee joint consists of the femur, tibia and patella. The femur (thighbone) is the bone connecting the hip to the knee. The tibia (shinbone) connects the knee to the ankle. The patella (kneecap) is the small bone in front of the knee. The fibula is a shorter and thinner bone running parallel to the tibia on its outside. The joint acts like a hinge but with some rotation.

The knee is connected by strong ligaments and surrounded by muscles. The muscles at the front of the thigh used to straighten the knee are the quadriceps and at the back to bend the knee are the hamstrings. The quadriceps tendon inserts into the patella at the top and the patella tendon comes off the bottom of the patella to attach to the tibia.

The ligaments of the knee joint stabilise the knee allowing it to function normally. The cruciate ligaments (anterior and posterior) are important structures, which guide the knee in its normal motion. Without these the knee often does not function normally and can result in instability or arthritis.

The medial ligament is on the inner side of the knee running from the femur to the tibia. The lateral ligament is on the opposite side of the knee running from the femur to fibula. These ligaments prevent sideways movement of the knee.

The knee is a synovial joint, which means it is lined by synovium, which produces fluid lubricating and nourishing the inside of the joint.

Articular cartilage is the smooth surfaces at the end of the femur and tibia. It is the damage to this surface which causes arthritis.

The meniscus is a specialised structure within the knee joint between the femur and tibia. There is a medial and lateral meniscus. These help distribute load, absorb shock, stabilise the knee and aid in lubrication.


What causes a painful knee?

When one or more parts of the knee are damaged it can become painful and movement becomes restricted. Over time, cartilage (the smooth covering at the ends of the bone in the joint) can crack or wear away. When this happens, the bones making up the joint rub together.

No matter your age, a knee problem may keep you from activities you enjoy. Pain and stiffness may even limit your day-to-day activities. Problems with the knee joint tend to build up over time.

Any of the problems below may lead to joint damage and hence knee pain:


As time goes by, normal wear and tear can add up. Cartilage may begin to wear away (osteoarthritis). As the bones rub together, they become rough and pitted. Previous meniscectomies and damage to the anterior cruciate ligament inevitably lead to osteoarthritis.


This is a group of conditions where the lining of the joint becomes inflamed and secretes material that destroys the joint cartilage. In these conditions more than one joint is usually affected. The joints are hot, swollen, painful and deformity is common.


This can occur for no reason (idiopathic) or can be secondary to a number of conditions (e.g. long-term use of alcohol or steroids). It is due to loss of blood supply to the bone. If the bone dies (necrosis), the joint will become arthritic. This pain often comes on quite suddenly and may increase rapidly. This can happen at any age. There are many other causes of this condition but they are rare.


A bad fall or blow can break (fracture) the bone. If the broken bone does not heal properly the joint may wear down like a tyre that is not balanced.


Injuries to ligaments causing instability of the knee can and usually do lead to premature arthritis.


Occasionally knee pain results from a problem which may have started in childhood such as osteochondritis dissecans, trauma, and juvenile rheumatoid arthritis. Note: Osgood-Schlatter disease does not cause arthritis.


Infection can destroy the cartilage lining, leading to osteoarthritis.


  • A bad injury that did not heal properly
  • Obesity
  • Long term exposure to sports or heavy manual labor
  • Long term high intensity, high mileage running (controversial)
  • Other rare diseases affecting bones or soft tissue causing severe pain in the knee and may lead to arthritis.

What is a unicompartmental knee replacement?

This 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. The knee joint is made up of three compartments; the patellofemoral (kneecap part), and the medial and lateral compartments between the femur and tibia (i.e. the long bones of the leg). Often only one of these compartments wears out, usually the medial one. If you have symptoms and x-ray findings suggestive of this, then you may be suitable for this procedure.

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 hence is not as traumatic to the knee, making recovery quicker.

What are the alternatives?

  • Non operative measures should be exhausted (e.g. weight loss, analgesics, modification of activities, anti-inflammatories, etc.)
  • Osteotomy, meaning cutting the bone and realigning it to put your weight through the good part of the knee.
  • Total knee replacement

What are the advantages and disadvantages of this compared to a total knee replacement?


  • Smaller operation
  • Smaller incision
  • Not as much bone removed
  • A 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
  • If, for some reason, it is unsuccessful or fails many years post the operation, it can be revised to a total knee replacement without difficulty.


  • Not quite as reliable as a total knee replacement in taking away all pain
  • Long term results not quite as good as total knee replacement

Who is suitable?

  • When pain and restricted mobility interferes with your lifestyle
  • One compartment involved clinically and on x-ray

Who is not suitable?

  • 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


There are some reported results in the literature of 98% 10-year survival, but most series report 10-year survival rates of 70-80%. There is continual improvement in design and instrumentation and results will continue to improve with this better technology.


  • 10 days prior to surgery, cease aspirin and anti-inflammatory medications (e.g. Voltaren, Feldene) as they can cause bleeding.
  • 10 days prior to surgery cease any naturopathic or herbal medications as these can also cause bleeding.
  • Continue with all other medications unless otherwise specified.
  • Notify Dr Walker if you have any abrasions, cuts or pimples around the knee.
  • Please bring any X-rays, MRI scans or other relevant investigations you have had done which may be relevant to your surgery.
  • You are advised to stop smoking for as long as possible prior to surgery.

You will have a pre-operative physician consult who will oversee medical problems post-operatively.

You will have completed a health questionnaire on your first visit in which you record your past and present illnesses, previous operations, medications and allergies. It is important to notify your surgeon of any changes in your medications or health status.

It is helpful to strengthen the muscles in your leg as much as possible before the operation. Useful exercises include cycling (gradually increasing to half an hour per day) and swimming with flippers.

Day of Surgery

You will be told what time to arrive and when to fast from.

The anaesthetist will see you prior to surgery.

You will be checked in by the nurse looking after you and prepared for surgery. You will then be taken to the operating room and have a drip inserted and monitors connected to measure vital signs during the procedure.

Surgical Procedure

A tourniquet is applied to the upper thigh and the leg is prepared for the surgery with a sterilising solution. An incision approximately 8cm long is made in the knee and the arthritic part of the knee is removed. Roughly 5mm of bone is taken from the femur and the tibia. This is replaced with special components cemented or press fitted to the femur and the tibia with a plastic insert placed in between.


You will wake up in the recovery room connected to monitors to measure your vital signs. You will have a bandage on your leg and usually a drain coming out of the operative site. You will usually have a button to press for pain relief. This will be explained to you by the anaesthetist. When you are awake and your observations are stable, you will be taken back to the ward.

Mobilisation will usually begin the next day. A physiotherapist will show you exercises to do and show you how to use crutches or a frame. The drain will be removed the next day and the dressing reduced.

When you are safe to go home, you will be discharged.


You will need assistance at home for the first week and will need to continue with your exercises. Physiotherapy will be arranged as required and can often speed recovery and motion. It is important to begin thigh strengthening exercises as soon as possible following surgery.

It is normal to take prescription pain killers for the first 3 – 4 days. Usually Panadeine is sufficient, it can be bought over the counter at the chemist. Pain and movement is very individual and hence recovery times vary enormously.
You should ice your knee 20 minutes at a time to reduce swelling for the first 3 – 4 days. When applying ice packs, ensure you place a wet cloth between your skin and the ice pack to prevent ice burn. Swelling can take weeks or even months to go down fully.

Crutches are for your own safety and to be changed to a walking stick or nothing when you are safe.
Normal activities can usually be resumed 6 weeks following surgery. You can drive a car when you can walk without crutches and have control of your leg. This is usually at 2-4 weeks. You must ensure you are in control of your vehicle before you drive.

The dressing you have when you leave hospital should remain intact until the first postoperative visit. If this leaks, it can be replaced with a clean dressing. If you have doubts about this it should be changed by your local doctor. You can shower in the dressing but do not bath or swim. If you get excessive swelling, redness, discharge or temperatures, contact the rooms immediately as these may be signs of infection. If it is after hours contact the hospital where the operation was performed and they will be able to contact the surgeon.

To minimise the risk of developing blood clots (DVT) it is recommended to take Cartia (aspirin, 100 mg per day) for 6 weeks. This can be obtained from the chemist without a prescription. TED stockings are recommended to be worn for 4 weeks. If you have risk factors for DVTs you may require other medications. All blood thinning medications have the risk of bleeding so it is always a balance between DVT risk and bleeding.

You may return to work and normal duties when your knee function improves enough for you to do your particular job. As a general guide you will be fit for sedentary duties after 3 weeks and a more manual-labour intensive job after 6 weeks. Work involving a lot of bending, kneeling or climbing stairs may take 3 months to return to.

Special precautions to take

  • Remember this is an artificial knee and must be treated with care.
  • In general, the more active you are, the quicker your knee will wear out.
  • Avoid situations where you might fall.
  • Your knee may go off in a metal detector at the airport. You can receive a note from the doctors rooms to say you have had a joint replacement.
  • Prevention of infection is vital. If you have any infections anywhere, make sure you see your local doctor straight away for treatment. If you get increasing pain in your joint and are sick and have a temperature, you should go to hospital to get checked out.

Antibiotics should be prescribed if you have an infection anywhere in the body or if you have surgery in contaminated areas such as teeth, nose, bowel or bladder, podiatry treatment or urinary catheterisation.


  • You should avoid pounding activities, which put a lot of stress on the joint.
  • Walking is good.
  • Swimming in a pool or light surf between the flags is safe.
  • Doubles tennis is allowable but anything more aggressive will lead to premature wear of your joint. Contact sports are forbidden and jogging can be detrimental to the long-term survival of your joint replacement.
  • Skiing on groomed slopes if you are a good skier is acceptable as long as you are aware you can cause significant damage if you fall.
  • Bowls and golf should not be a problem.

Risks and Complications

Any operation, big or small has risks. The following can occur with any surgery and some rarer complications may also be possible. It is impossible to discuss every complication and there will be some which no surgeon may anticipate or may never have heard of. The utmost care is taken at all times during surgery to prevent these complications.

Some complications specific to unicompartmental total knee replacement are:

  • Infection
  • Fracture
  • Stiffness
  • Damage to nerves or blood vessels
  • Blood clots
  • Wound irritation or breakdown
  • Wear
  • Osteolysis
  • Damage to ligaments
  • Dislocation
  • Heterotopic ossification
  • Cosmetic appearance
  • Leg length inequality
  • Breakage of the implant

The following list is not exhaustive. For more information on these complications:
Knee Replacement Complications


This is an excellent operation in the right patient. The biggest advantage is that it feels more like a normal knee and is a quicker to recovery time. Its biggest disadvantage is that it is not quite as reliable as a total knee replacement and may not last quite as long. If, for some reason, it does not relieve your pain, then it is relatively easy to convert it to a total knee replacement. By far the majority of people are happy with their joint replacement.

Although there is a lot of information above, it is important to read it all so you can make an informed decision to undergo surgery. You must not proceed until you are confident that you understand this procedure and particularly the complications.