Unicompartmental Knee Replacement (UKR)

Partial knee replacement / Knee resurfacing / Patello-femoral replacement

The knee joint is made up of the lower end of the thigh bone (femur), the top end of the shin bone (tibia) and the kneecap that lies at the front of the knee.  The joint itself is lined with cartilage that provides a smooth surface for the joint to move in a smooth pain-free manner.  With arthritis, the cartilage layer gets worn away exposing the bone surface underneath resulting in pain and stiffness of the joint.  Most commonly, all areas of the knee are affected and the solution is a total knee replacement.  However, some patients have a pattern of wear that only affects one section of the knee.  Usually this is the medial (inner) bearing, but it can also occur in the lateral (outer) bearing or the patella-femoral joint at the front of the knee.

If your pattern of arthritis is suitable (usually evident on x-ray but sometimes requiring a scan) and your symptoms are intrusive you may be a candidate for a partial knee replacement – a more limited operation than a total knee replacement that only resurfaces the sections of your knee that are damaged, leaving the other sections with their natural cartilage surface.  The potential advantages are that this can be achieved through a smaller incision with less soft tissue trauma, therefore less pain and a quicker average recovery.  There is also a better chance of the knee function feeling more natural, and achieving a greater range of movement.

Your surgery is likely to be carried out under a spinal anesthetic with an injection in the lower back that results in you loosing the feeling in your legs for a few hours.  You will then be offered sedation whilst the surgery is being carried out or you can listen to music or watch a film with some headphones.  The surgery takes 60-90 minutes.

Following your operation your knee will have a compression bandage which remains in place for the first 24-48 hours.  Once your spinal anaesthetic has worn off and the sensation has returned to your legs, under the supervision of either the physiotherapy team or nursing staff on the ward you may be able to start gentle bending exercises and standing / walking on the day of your surgery.  Within the early post-operative period you will use an ice-pack on your knee to help reduce and manage the swelling that occurs as a result of the surgery.  This also can help reduce your pain and aids your recovery.

Factors to Consider

What are the risks of surgery?

Before your operation your surgeon will explain in detail the nature of the surgery, the outcome you should personally expect, and the risks of surgery.  

Below are some of the main risks of knee replacement surgery:

  • Deep Infection – this risk is less than 1%.   The majority of wound infections are surface skin infections that can be treated with a course of antibiotics.  If a deeper joint infection occurs then this may require a further operation firstly to wash the joint out with saline and then treat with antibiotics via a drip.  If this is unsuccessful the knee replacement may need to be taken out in order to remove any bacteria and then a new knee replacement re-implanted a few weeks later when the knee is completely free of any infection.
  • Blood clots in the leg (Deep Vein Thrombosis - DVT) and blood clots in the lung (Pulmonary embolus- PE) – the overall risk of a serious blood clot is less than 1%.  You are at risk of a blood clot following knee surgery due to reduced activity during the initial post-operative period and the leg swelling following surgery.  To reduce this risk we encourage you to mobilise as soon as possible after your surgery even with simple calf stretches whilst you are still in bed.  We use special pumps on your calves during and after surgery and you will also be prescribed a tablet to thin the blood slightly which you will take for 2 weeks after your operation.  All of these strategies reduce the risk of blood clots but we cannot eliminate it completely.
  • Nerve damage – you will experience a numb sensation over the front of the knee following surgery.  This is because small nerves that supply the sensation to the skin over the front of the knee are cut during surgery.  This area will usually shrink over a few months but some reduced sensation will often remain permanently.
  • Revision surgery (repeat) – sometimes knee replacements can wear out after several years and become loose causing renewed pain and swelling.  The un-resurfaced sections of your knee may also get progressive wear, but this would be uncommon in the first decade.  If this happens then it is possible to remove the worn out knee replacement and replace it again, but the operation is more complex.  However, it is more straightforward to re-do a failed partial knee replacement than a worn-out total knee replacement.
  • Persistent pain – following surgery over 95% of patients have effective pain relief, but a small percentage of patients can still have annoying discomfort for which a cause may not be found. 


Important: this information given above is only a guideline as is not complete.  For more information or to book an appointment please contact us.   

After Surgery


Stage 1

  • Pain control
  • Swelling reduction with ice therapy and leg elevation when resting
  • Walking with frame/sticks with assistance
  • Sitting out in chair (2-4 hours during day)
  • Eating and drinking normally
  • Bulky bandage from theatre reduced

Stage 2

  • Walking more independently short distances (to bathroom) but assistance for longer distances
  • Aim to become more mobile throughout the day
  • Sitting out in chair for longer periods
  • Pain control still required regularly
  • Ice therapy to control swelling (which may be more than day 1 post-op)
  • Sleeping becomes more settled

Stage 3

  • Mobilising independently
  • Managing stairs confidently unaided
  • Aiming for a bend of the knee of approximately 70-90 degrees on discharge
  • Pain management well controlled with standard painkillers
  • Continued ice therapy to knee to help with swelling 
  • Wound clean and dry with no fluid oozing
  • Mentally feeling ready and confident to leave the hospital and return home

Stage 4

  • Once over the initial post-operative period the focus over the next few weeks and months is to increase the range of movement of your knee to approximately 120 degrees bend and to fully straighten the knee.
  • Continue to develop strength and confidence on the knee
  • Consider returning to work between weeks 6-8 post-operatively
  • Driving when confident beyond 6 weeks post-operatively not before
  • The aim of knee replacement surgery is to achieve a knee that you forget has been replaced but this can take up to a year to achieve