Revision Knee Replacement
Total Knee Replacement (TKR) is a very successful treatment for end-stage degeneration of the knee joint; almost 60,000 TKRs are performed in the UK each year.
Despite technological advances and our increased understanding of knee replacement surgery, between 5-10% of knee replacements will fail and require revision within 10 years.
The most common cause of knee replacement failure is aseptic loosening due to implant wear, although other factors such as infection, trauma and metal sensitivity can all result in the need for revision surgery.
The majority of knee replacements consist of metal femoral and tibial components with a plastic (polyethylene) liner inserted between the two – the articulating surfaces. Although these modern implants are designed to withstand the substantial forces that are transmitted across the knee joint during everyday activities (e.g. up to 7 times body weight when going up or down stairs), the friction of the articulating surfaces results in wear of the plastic liner over time.
As the plastic liner wears, small particles of polyethylene are generated. These particles then activate the body’s immune system, triggering an inflammatory response and causing the bone around the knee replacement to be reabsorbed. The result is that the knee replacement becomes loose and painful; this is known as aseptic loosening. As a consequence the knee replacement often needs to be revised.
Knee replacements are subjected to greater amounts of wear in patients who are young, active or overweight. The rate of failure is therefore higher in these patients.
Wear will also be greater if the knee replacement is not correctly aligned or not securely fixed to the bone and if the ligaments are not ‘balanced’ with the correct tension. All of these are factors are dependent upon good surgical technique. It is important therefore that knee replacements are undertaken by orthopaedic surgeons who specialise in this field.
Current studies show that cemented knee replacements are a better method of fixation, in terms of long-term survival, than uncemented systems.
A small percentage (about 0.5-1%) of knee replacements become infected. If the infection is suspected quickly enough, surgery can be undertaken to wash out the infected knee replacement, change the polyethylene liner and thereby clear the infection. High doses of intravenous antibiotics are then required for a period of generally 6-12 weeks to ensure that the infection doesn’t recur.
Occasionally the infection persists and the knee replacement must then be removed and a temporary ‘spacer’ inserted. Once the infection has cleared, revision surgery can be performed, usually at least 3 months later.
The possibility of infection should be excluded by tests before any revision knee replacement surgery is performed. These tests include blood tests (inflammatory markers), x-rays, possibly a bone scan and often a biopsy of the tissues around the knee replacement.
Trauma, such as a fall that causes a fracture of the femur or tibia around a knee replacement, can result in failure of the TKR. Often the fracture can be fixed and the knee replacement left in place, but occasionally revision knee replacement is necessary (see picture).
Metal sensitivity has recently been identified as a cause of knee replacement failure; patients who are sensitive to metals (usually nickel) have an unacceptably high rate of failure with knee replacements.
Metal-sensitive implants such as Oxinium™ are now available (see Knee Replacement) and should be used in all patients with a suspected history of metal sensitivity.
Revision knee replacement surgery involves an inpatient stay of 7-10 days. The surgery is complicated, technically demanding and whilst the risks are the same as for primary TKR, the rate of complication is much higher. It should be undertaken by surgeons who have an interest in and are specialised in revision knee surgery.
Revision knee replacements are performed under a combined (spinal and general) anaesthetic. The old knee replacement is removed with great care in order to protect the surrounding bone. Often there has been significant bone loss as a result of aseptic loosening; a bone graft or additional prosthetic implants may be necessary to allow the revision knee replacement to be properly aligned and stable. Revision knee replacements usually need an extension (called a ‘stem’) in the femur and tibia so that there is adequate support.
At the end of the operation a drain is inserted into the knee joint to draw off excess blood. A dressing is applied to the wound and the knee will be wrapped in a crepe bandage. Foot pumps, elastic stockings and occasionally an injection to thin the blood are used to lower the risk of blood clots forming in the legs.
No two revisions are the same; possible difficulties encountered are bone loss, ligament insufficiency, infection and stiffness. Highly specialised implants may be necessary and the results are not as good as for standard primary knee replacement. However, the majority of patients are very satisfied with the results of revision surgery and obtain very good relief of pain and return to function.
The postoperative recovery from revision knee surgery is similar to that of primary knee replacement but occasionally a brace is needed for the first few weeks in order to protect the soft tissues while they heal. Physiotherapy is essential to assist patients in mobilising after the operation.