Robotic arm assisted Uni-compartmental Knee Replacement

Uni-compartmental Knee Replacement

What is it?

Uni-compartmental or uni-condylar knee replacement is where only one part of the knee is replaced. It used to treat arthritis (wearing away of the smooth articular cartilage).

It is commonly referred to as half a knee replacement and is mostly used to replace the inner (medial) arthritic part of the main knee joint. Ideally, the outer half of the knee should be unaffected by arthritis as should the patello-femoral (kneecap) joint. However, with the latter, mild arthritis may be accepted, as this has been shown to not negatively affect outcome in most cases.

The potential benefits of this surgery when compared to a total knee replacement are that the amount of bone removal is less; a smaller incision is used and less blood loss occurs. These factors shorten the recovery time.

Who should have uni-compartmental knee replacement?

Arthritis manifests with varying degrees of pain, swelling, restriction of movement and function. The joint surfaces become globally rough due to the wear of the smooth articular cartilage and the joint often feels stiff and can become tuckor lock.

Non-operative treatments include but are not limited to, physiotherapy, analgesia, cortisone injections, joint supplements and weight loss.

The decision to undergo any form of replacement surgery should be based around your quality of life; surgery is usually considered the last resort option, particularly when other treatment is not adequate or is no longer beneficial, thus leading to deterioration in quality of life.

Uni-compartmental knee replacement may be considered if:

  • Arthritis only affects one part (compartment) of your knee
  • You are not obese
  • The anterior cruciate ligament is intact
  • You do not suffer from an inflammatory condition such as rheumatoid arthritis
  • The knee fully straightens and bends past 90 degrees

Mr Patel will discuss the decision to undergo surgery with you in detail at your consultation.

Will I need any tests/scans?

X-rays will be requested for all cases. MRI can be used to ensure that other parts of the joint are not affected by arthritis, or in some circumstances, a diagnostic knee arthroscopy may be performed to accurately assess the joint. Please see the section Surgery FAQs to see if you will need any other tests e.g. blood tests before your surgery.

How is it done?

The surgery is usually carried out under general anaesthetic. A tourniquet is applied and inflated. The incision is made at the front of your knee, just towards the inner side. The worn areas of the joint are removed and the implant is fixed into place, usually using special bone cement. The implant is essentially made up of two metal alloy parts and a polyethylene (high grade plastic) insert. The movement and stability of the joint are checked.

Partial knee replacement can now be carried out using robotic-arm assisted surgery (Stryker-MAKO). Mr Patel is an early advocate of this technique and can discuss this in detail with you at your appointment.

The wound is closed with sutures and clips and a small drain is inserted to help remove excess fluid in the first 24-48 hours. A dressing and bandage are then applied.

The procedure normally takes between 1-2 hours.

Post-operative X-ray of an unicompartmental knee replacement

How long is the hospital stay?

Your stay in hospital will approximately be between 3-7 days. Safely regaining mobility with crutches and being able to go up and down stairs are pre- requisites for discharge. Post-operatively, a blood test and an X-ray will be taken. The drain will be removed on the ward.

What about after I leave hospital?

You will see a physiotherapist before discharge to be instructed on crutch use and simple exercises to carry out in the short term. Crutches are advised for approximately 4-6 weeks, but this varies from patient to patient.

You will be allowed to weight-bear as tolerated in most cases. Swelling of the knee and lower leg and bruising is very common after uni-compartmental knee replacement and is to be expected. It may persist for several weeks until full range of motion and mobility has been regained.

You will be prescribed analgesia to take home and Mr Patel strongly advocates its use to keep pain to a minimum; it should be noted that pain is more difficult to control if it is allowed to establish itself. Mr Patel recommends the regular application of ice as an adjunct to relieve pain and swelling in the acute post-operative period. You will also be prescribed anti-coagulant medication to take for a further 14 days or until you are fully mobile. This is to minimise the risk of a deep vein thrombosis.

You will see Mr Patel two weeks after surgery for a wound check (and stitch/clip removal) and a physiotherapy program will ensue thereafter which is paramount to the success of the operation. You are likely to have been seeing a physiotherapist before the operation and Mr Patel will liaise with him/her in detail to advise on the post-operative exercise program.

Total recovery time is between 4-6 months. Gradual improvement is seen during this period and Mr Patel advises driving can resume once he has seen you and consented.

It is good and common practice to keep uni-compartmental and total knee replacements under regular review to ensure they are performing adequately. Thus routine follow up should be organised. Mr Patel would like to see you for clinical examination and X-ray your knee at the following post-operative intervals:

  • 6 weeks (no X-ray required)
  • 6 months
  • 1 year
  • 2 year
  • 5 years
  • 10 years
  • Every 5 years after that

What are the potential complications?

All surgery carries a risk. Specific risks to uni-compartmental knee replacement are:

Infection this can be either superficial (wound) or within the joint. Antibiotics will be given to reduce this risk.

Thrombosis a clot in the deep veins of the lower limb (DVT). The risk is minimised by early mobility and anti-coagulant medication. Oral contraceptive pills and HRT, which are known to increase risk, should be stopped before surgery. Mr Patel will advise you on this.

Bleeding this may require a return to the operating room for removal of blood clots and to stop the bleeding.

Stiffness It is very important that some mobility of the knee is maintained after surgery. The physiotherapist will advise on simple exercises that can be carried out at home. Mr Patel also recommends that you take regular analgesia and use ice (see Surgery FAQs) to help minimise post- operative discomfort and facilitate early movements

Loosening the implant can become loose, either due to infection or as a function of time. It will need to be replaced in either case.

Residual symptoms unfortunately, no guarantees can be offered regarding curing your symptoms, despite the surgeons best efforts. In this case, further management and treatment options will be discussed with you.

For private patients

The Wellington Hospital
The Knee Unit
Wellington Place
London NW8 9LE

Tel: 02074835059
Fax: 020 7483 9131
PA Email:

The Schoen Clinic
66 Wigmore Street
London W1U 2SB

Tel: 02074835059
PA Email:

For NHS patients

University College London Hospital
2nd Floor Maple House
149 Tottenham Court Road
London W1T 7BN

Tel: 02034479413
Fax: 020 7380 9081
PA Email: