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Uni condylar Knee Replacement

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Unicondylar Knee Replacement simply means that only one 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.


Arthritis is a general term covering numerous conditions 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 but often the exact cause is unknown. In general, but not always, it affects people as they get older (Osteoarthritis).

Other Causes Include

  • Trauma (fracture)
  • Increased stress e.g., overuse, being overweight, etc.
  • Infection
  • Bleeding disorders
  • Connective tissue disorders
  • Inactive lifestyle- e.g., Obesity, as additional weight puts extra force through your joints which can lead to arthritis over a period of time
  • Inflammation e.g., Rheumatoid arthritis

In an arthritic knee

  • The cartilage lining is thinner than normal or completely absent. The degree of cartilage damage and inflammation varies with the type and stage of arthritis
  • The capsule and joint lining of the arthritic knee may be swollen
  • The joint space is narrowed and irregular in outline; this can be seen in an X-ray image
  • Bone spurs or extra bone (osteophyte) can also build up around the edges of the joint

The combinations of these factors can make the arthritic knee stiff and limit activities due to pain and/or fatigue.


  • The diagnosis of osteoarthritis is made on history, physical examination & X-rays
  • There is no blood test to diagnose Osteoarthritis (wear & tear arthritis)

Advantages & Disadvantages

The decision to proceed with any knee replacement surgery is a cooperative one between you, your surgeon, your family and your GP.

The desired benefit following surgery is 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
  • Deformity- either 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, walking sticks or physical therapy.

Potential advantages of uni-compartmental replacement

  • Smaller operation
  • Smaller incision
  • Not as much bone removed
  • Shorter hospital stay
  • Shorter recovery period
  • Blood transfusion rarely required
  • May feel more like a ‘normal’ knee


Long term survival results are not as good as total knee replacement

Who is suitable and who is not?

  • Ideally should be over 50 years of age
  • When pain and restricted mobility interferes with your lifestyle
  • One compartment involved clinically and confirmed 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


  • Your surgeon will send you for routine blood tests and any other investigations required prior to your surgery
  • You will be asked to undertake a general medical check-up with your GP
  • You should have any other medical, surgical or dental problems attended to prior to your surgery
  • Make arrangements for help around the house after 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

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 anaesthetist, who will ask you a few questions
  • You will be given a hospital gown to change into prior to surgery
  • Approximately 30 minutes prior to surgery, you will be transferred to the operating theatre
  • The operation site will be shaved and cleaned

Surgical Procedure

Each knee is individual and knee replacements take this into account by having different sizes for your knee.

Surgery is performed under sterile conditions in the operating theatre under spinal or general anesthesia. You will be on your back and a tourniquet (padded strap) will be applied to your upper thigh to reduce blood loss. Surgery will take approximately one-two hours.

The Patient is positioned on the operating table and the leg prepped with antiseptic solution and draped.

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 implanted with or without cement.

The knee is then carefully closed with suturing and drains may be inserted, and the knee is then dressed and bandaged.

Post-operation Course

When you wake, you will be in the recovery area with intravenous drips in your arm, potentially a tube (catheter) in your bladder and a number of other monitors to check your vital observations. You may have a button to press for pain medication called a PCA machine (Patient Controlled Analgesia). Your anaesthetist may have performed a nerve block procedure to ‘numb’ the leg.

Once stable, you will be taken to the ward. The post-op protocol is surgeon dependant, but in general any drains will come out at 24 hours and you will sit out of bed and start moving your knee and walking on it as early as the day of surgery. The dressing will be removed on the 1st- 2nd post-op day to make movement easier. Your rehabilitation and mobilization will be supervised by a physiotherapist.

To avoid lung congestion, it is important to perform deep breathing exercises and cough up any phlegm you may have.

Your surgeon will use one or more measures to minimize the risk of blood clots in your legs, inflatable pumps, leg stockings and injections into your abdomen to thin the blood to prevent clots or DVT’s, which will be discussed in detail in the complications section.

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

Usually you will remain in the hospital for 1-3 days. Depending on your needs, you will then return home. You will need physiotherapy on your knee following surgery.

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

Your sutures are sometimes dissolvable but if not, stiches and clips require removal at approx 12-14 days.

Bending your knee is variable, but by 6 weeks it should bend to 90 degrees. The goal is to obtain 120 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 and can do an emergency stop without pain. You should be walking reasonably comfortably by 6 weeks.

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

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

You will need to continue working on an exercise program as demonstrated by the physiotherapists while an inpatient (in hospital). Formal physiotherapy will be required following surgery. This will usually start after the acute phase of recovery, 2 weeks or so after surgery when the wound has healed.

You will usually have a 6 week check up with your surgeon, who will assess your progress. More long term follow up to monitor progress is likely to be required.

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 can find their way to your knee.

If you have any unexplained pain, swelling, or redness or if you feel generally unwell, you should see your GP or surgeon 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 understand 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 anaesthetic and those affecting medical health. Almost any medical condition can occur so this list is not exhaustive. 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 knee, 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. If deep infection is present, your knee replacement may need to be removed to eradicate infection.

Blood Clots (Deep Venous Thrombosis)

These can form in the calf/thigh veins and can travel up 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/GP.

Fractures or breaks in the bone

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

Stiffness in the Knee

Ideally, your knee should bend beyond 100 degrees but on occasion, it may not bend as well as expected. Sometimes manipulations are required. This means going to the operating theatre where the knee is bent for you while under anesthetic.


The plastic liner eventually wears out over time 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 massage of the wound 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 looked pre-operatively as the alignment is corrected.

Leg length Inequality

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


An extremely rare complication 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).

Patella Problems

The Patella (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 this occurs and is recognised intraoperatively, neurovascular structures 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 any concerns thoroughly with your surgeon at ‘The Cambridge Knee’ 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 when non-surgical treatment has failed. It is a big decision to make and ultimately it is an informed decision between you, your surgeon, your family and your general practitioner.

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

RCS Logo British Orthopaedic AssociationRoyal College of Surgeons of EdinburghOTSISBritish Association for knee surgeryISOAMDU LogoOTSIS