Knee Replacement - Outcomes & complications

Authored by Dr Jacqueline Payne, 04 Jul 2017

Patient is a certified member of
The Information Standard

Reviewed by:
Dr Helen Huins, 04 Jul 2017

For the majority of people knee replacements are very successful. There is a lot of evidence from research showing that patients have less pain and are much more mobile after surgery and this often greatly improves their quality of life. Outcomes are getting better too, as more research is carried out on what the best operation is and how to reduce the risk of complications.

However about 8 people out of 100 are unhappy with their knee replacement 2-17 years later. If they have had to have their knee replaced a second time (revised), they are twice as likely to be unhappy with the outcome.

Within about 8 weeks of your operation, you will be followed up by the hospital where you had your surgery. You will usually be offered further follow-up appointments.


Blood transfusion may be needed.

Pain & stiffness

  • Pain can be reduced by different anaesthetic techniques used at the time of your operation.
  • It is important to make sure that you get adequate pain relief. You need to be able to move about and then start to walk as soon as you are able after your operation.
  • It is extremely important to follow the advice from your physiotherapist regarding exercises to do following your knee replacement:
    • In particular, not moving the knee enough can cause the scar and the tissues around the knee to 'glue' up.
    • Occasionally this has to be treated by forcefully moving the knee under anaesthetic, followed by intensive physiotherapy.

Venous thromboembolism

  • Venous thromboembolism occurs when a clot of blood forms inside a vein.
  • All patients are given thromboprophylaxis (medication, foot pumps, below knee stockings) - unless it would be dangerous to do so. (Thromboprophylaxis is the name for anything that reduces the chance of getting a venous thromboembolism).
  • This reduces the chance of suffering from the most severe but rare form of thromboembolism, which is a pulmonary embolism (PE). It reduces the risk of dying from a PE by 70%.
  • If you have already had a venous thromboembolism before or are closely related to someone who has, this makes it more likely that you will suffer from one when you have your knee surgery. Cancer and chemotherapy, as well as being obese, also increase your risk of this complication.

Nerve damage

  • It is common to have a numb area of skin to the outer side of the operation scar.
    • This may improve over 2 years but doesn't always recover completely.
  • Occasionally a particular nerve, called the common peroneal nerve, is damaged during a knee replacement.
    • This can cause foot drop.
    • Foot drop weakens your foot so that you don't lift the front of your foot properly as you walk.
    • Peroneal nerve damage is more common when the arthritis in the knee is very severe.
    • Half of the people who develop foot drop recover completely without any treatment.

Ligament damage

  • There are four ligaments that cross the knee and sometimes they can be damaged during a knee replacement.
  • If one of your knee ligaments is damaged it may be possible to mend it during the operation or you may have to wear a brace around your knee for a while to allow it to heal.

Blood vessel damage

  • Damage to the blood vessels is rare.
  • If it occurs it would usually need further surgery to repair it.

Other complications include:

  • Urinary tract infection - related to having a tube (catheter) put in your bladder during the operation.
  • Constipation - due to painkillers and immobility.
  • Chest infection - more likely following a general anaesthetic and in people who already have a lung condition, such as chronic obstructive pulmonary disease (COPD).
  • Wound infection and wound breakdown (also knee joint infection - see below).
  • Painful scar - this may make it difficult or uncomfortable to kneel and some people avoid kneeling after a knee replacement for this reason.
  • Dislocation of the knee - this is rare but can occur with certain types of knee replacements.
  • Fracture - of the femur or tibia - or breakage of a prosthesis is rare.

Long term complications include the knee replacement 'failing' and infection of the knee joint:


  • Knee replacements can wear out; they can become loose or break - this is often referred to as knee replacement failure. They then need to be re-done (revised) which is a much more complex operation.
  • Pain after surgery, instability and stiffness are other reasons for knee replacement revision.
  • Needing to have your knee replacement done again is more likely the younger you are when you have it done in the first place:
    • 3½ years after your operation you are 5 times more likely to need to have it revised if you were under 55 when you first had it done than if you were over 75.
  • Overall about 4-6 out of every 100 people who have a knee replacement will need to have it revised within 10 years.
  • On the other hand, for between 80 and 90 out of every 100 people, their knee replacement lasts more than 20 years.
  • Your knee replacement is likely to last longer if you are not obese or overweight and if you don't do a heavy manual job.


  • Infection of a knee replacement can be catastrophic. An infected knee prosthesis may need to be removed and it may not be safe or possible to replace it.
  • Between 1 in every 100-200 people who have a knee replacement get a knee joint infection.
  • The risk of infection is greater in men but it is not known why this is.
  • 8 out of every 10 people who get a joint infection, do so within the first year of their operation.
  • In one study, 1 in 4 of the people who got a knee joint infection, never got rid of it completely. This causes significant long term disability.

Further reading and references

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