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There are risks following knee replacement surgery despite high standards of practice. Complications can occur that may have permanent effects which is why the operation is only undertaken when all other methods of treatment have failed. Surgeons do not usually outline every single complication but they do point out to you the most serious ones.   Serious complications occur in no more than one or two in every 100 patients, but less serious complications can occur more frequently and generally get better.  

General risks of surgery  

Possible complications include:

  • Pain around the incision.
  • Nausea – often from the anaesthetic.
  • Heavy bleeding from the surgical site.  A blood transfusion may be required. Sometimes patients are asked to donate their blood in advance and there are sometimes systems which collect the blood that has leaked into the drains and this is then re-transfused.
  • Keloid or thickened, raised scars – these can be very unpleasant, itchy and unsightly in  the early stages but usually will settle down and are not a serious threat to the wound healing.
  • Separation of the wound edges – sometimes the stitches or clips come adrift and this can cause opening of the wound.
  • Allergies to anaesthetic agents, antiseptic solutions, suture materials or dressings.
  • Very rarely there may be any complication of anaesthesia and surgery such as blood loss, heart attack, heart failure, stroke, kidney failure, and other serious problems.

Specific Risks of Knee Replacement


Infection around the prosthesis occurs in about one patient in every 100, and is very serious.  It can occur immediately or many months after the operation.  Infection can spread from any part of the body.  To help prevent this antibiotics are given before and after surgery.   You may need to take antibiotics during other subsequent surgery.  Sometimes a small operation to clean out the knee may be required. Occasionally the infection may be resistant to treatment and a second operation may be needed to remove the components of the knee replacement. Once all the infection has been effectively treated a third operation is performed to insert new components. You may develop other infections including chest and urine.

Thrombosis and Pulmonary Embolism:

Blood clots can form in the deep veins of either leg. This can be life-threatening if they break away from the vein wall and travel in the bloodstream to block the arteries to the lung.  Prevention in the form of injections, tablets or special leg pumps is used.  


The prosthesis may become loose where the metal or cement meets the bone.  This can cause pain and eventually another operation may be needed.  This is the most common long-term problem. The prosthesis may loosen if osteoporosis (loss of bone density) occurs.  Rarely, the artificial joint may break and another operation would be needed.

Scarring, Stiffness and Swelling:

Heavy scarring after surgery may restrict bending of the knee. To release the scars and improve movement the Surgeon may need to manipulate the knee.  If the joint was extremely stiff before surgery, there is likely to be quite a lot of stiffness afterwards. Swelling is common after surgery and may take several months to settle. Occasionally it may be necessary to drain fluid off with a needle.

Nerve and Artery Injury:

A major nerve may be damaged, leading to poor or no leg movements.  Most nerve injuries recover well, often completely.  Uncommonly, nerve damage may be permanent, leading to permanent numbness and/or weakness of the foot.   One of the major arteries near the knee may be injured and require further surgery.   


A numb area of skin, usually on the outer side of the wound, is quite normal and most of this will recover with time. Occasionally, blisters may develop which usually heal without any problem.


Rarely, complications due to a severely impaired blood supply, arterial damage or overwhelming infection may lead to amputation of the leg above the knee.  The risk is greater for patients who are elderly or in poor general health.  The overall risk is 1 patient in 6,000.   


The prosthesis may become loose requiring further surgery; this can be done in one operation.  If the looseness is due to infection, this will usually require two operations with a period of 6 weeks to 6 months between them to allow the infection to settle.