The vast majority of patients make a good recovery after their knee replacement operations and experience no serious problems. However it is important you understand that a knee replacement is a major operation and that complications can occur.

General surgical risks

Thromboses and emboli (blood clots)

Blood clots in the leg veins (deep vein thrombosis) and blood clots on the lungs (pulmonary embolus) are a risk associated with joint replacement surgery.

The simplest way of reducing this risk is early mobilisation (exercises and walking).

Whilst in hospital you may also be prescribed blood thinning treatment, usually in the form of tablets. These tablets reduce the risk of clot formation.

Patients already receiving anti-coagulant therapy will be assessed and advised accordingly. After discharge, it is important that you inform your General Practitioner if you notice increasing swelling in your calf accompanied by pain; chest pain or if you start coughing in the early weeks after surgery.

Urinary problems

Some patients, particularly those who may have previously experienced difficulty passing water, may sometimes need a catheter to be inserted into the bladder prior to or after the operation. Except in certain circumstances, this should be removed the morning after surgery.


Nowadays, blood transfusion following a knee replacement is rarely needed. If your blood count is very low or if you are showing symptoms of anaemia (low blood count), the team looking after you may recommend a blood transfusion.


Most joints are made of stainless steel or cobalt chromium and polyethylene. A very small level of nickel is present. It is extremely unlikely that you will have an allergy to your implant even if you have experienced a rash to your watch or earrings. Tell your surgeon if you are concerned.

Superficial infection

You will not be discharged from hospital unless the appearance of the wound is satisfactory. After discharge, if you have any concerns about your wound, please inform your GP or Practice Nurse.

Deep infection

A deep infection of the joint most often starts when bacteria gain access to the tissues at the time of surgery and great lengths are taken in theatre to reduce the risks of this happening. Operations are carried out in an ultra-clean air theatre and sterile clothing is worn by the surgical team. You will be given preventative antibiotics at the time of surgery. All patients are screened for MRSA during their Pre – Assessment Clinic appointment. If you are found to be a carrier of MRSA you will be given treatment prior to your operation. A specimen of your urine taken to your Pre – Assessment Clinic appointment will be screened for bacteria. If bacteria are found in your urine, you will be informed and treatment given if needed. Despite all the precautions taken, infections can still occur.

An early deep infection (within the first six weeks) may sometimes be treated by washing the joint out in theatres, followed by an extended course of antibiotics. However, it is sometimes necessary to remove the new knee, treat the infection with a long course of antibiotics and then replace the knee again at a later date. An infection can occur at any stage in the life of a knee. The reason for this is that any infection in the body can circulate in the blood and settle on the surface of the new knee joint. Once there it forms its own environment, or ‘bio-film’, which makes it difficult to treat with antibiotics alone. Although the symptoms of infection can often be suppressed with antibiotics the only way to eliminate this deep infection is to remove the artificial implant as described above. If you develop signs of an infection (e.g. urine or chest infection, tooth abscess, leg ulcer) at any time after your operation, please remind your GP/dentist that you have a knee replacement. If your knee suddenly becomes painful, it is important to see your GP so that infection in your knee replacement can be ruled out.

Remember infection is a serious complication. If you develop any new redness around the wound or if the wound leaks after leaving hospital, it is important that you see your GP.


It is common to see bruising around the knee in the days after surgery and, occasionally, this bruising will extend down the leg, sometimes into the foot.


You may find your knee and lower leg swell. This is a normal response to surgery. It may be many months before this settles. Often the shape of the knee is altered. Occasionally, the knee will always remain slightly larger than a normal joint.

Some warmth around the knee is another common occurrence and is due to increased blood flow through the tissues during healing. Again, this may take many months to settle. You should continue to do the exercises detailed in this link even if your knee is swollen. Walking can help reduce the swelling, but standing unnecessarily should be avoided. You should also aim to lie flat for at least 20 minutes once or twice a day. Whilst lying, it may be beneficial to elevate the leg ideally with “foot higher than heart”.

If the swelling does not reduce over night or is accompanied by tenderness in the calf or groin, a temperature or breathing problems you should ask your GP for advice.

Medical problems

Complications of myocardial infarction (heart attack), stroke or death can occur after knee replacement as with other forms of major surgery. These complications are very rare and the anaesthetist will not allow the operation to proceed if it is felt that the risks are significantly higher than normal. In this circumstance, it may be that you are sent for further tests or treatment prior to surgery being performed.

Specific risks

Stiffness and range of movement: Most people are delighted with their knee replacement. Some people describe aching or stiffness in the joint or have a limp which does not improve. It is vital to follow your rehabilitation programme to achieve the best possible outcome. It can take many months to gain a good range of movement. The ease and range of movement with a knee replacement will vary from person to person. This is due to many factors such as:

  • your general health before the operation
  • the position of your knee before the operation
  • the range of movement before the operation
  • the medication you are normally prescribed
  • your weight
  • Any post-operative complications