Total knee replacements usually function well to reduce your pain and improve mobility and function. Approximately 90% of TKR’s will survive to 20 years.
Occasionally, the knee replacement becomes more painful and possibly unstable. In these cases, the cause of the increased pain is determined by special investigations.
Essentially, revision surgery involves removing the old implant carefully minimising bone loss and implanting a more complex knee replacement which is usually more constrained and may use cement and stems in the tibia and femur to increase the implant’s stability.
It is a bigger operation compared to the first knee replacement in terms of operative time, technical difficulty and risks.
Why does a TKR fail?
Within the first 5 years
Component mal-position or sizing issues (leading to stiffness or instability)
After 5 years
The TKR on the left has clearly failed and has been revised to a stemmed implant Post operative X-rays of a revision TKR
This complication occurs in 0.1-0.5% of TKR’s. It could happen due to infection at the time of surgery or at a later stage (eg infection elsewhere in the body causing septicaemia and subsequent infection of the TKR). It is vital that the organism causing the infection is isolated. This is done by an aspiration or arthroscopy of the joint. If an organism is isolated, a 2 stage revision is performed. The first stage is to remove the old implant and remove all infected tissue from the knee joint. A temporary spacer is implanted to allow partial weight bearing and some movement. The interim period consists of intravenous then oral antibiotics until the infection has been eradicated (normally about 6 weeks). The second stage is implantation of another knee replacement. This one will usually have stems going into the tibial and femoral canals to secure the new knee replacement firmly. Sometimes it is possible for me to do this revision as a one stage procedure (ie without the interim period)
At the time of surgery, the size of the implant is sized for each patient. Over or underestimation of the size can lead to problems with stiffness or instability.
Over the years the metal femoral component slowly wears away the surface of the strong plastic insert. The particles of plastic cause a reaction with the body’s immune system which results in the bone around the TKR being weakened. This can lead to loosening of one or more of the components. This may present as pain or instability.
Possible investigations prior to revision surgery
Blood tests / blood cultures
Nuclear medicine bone scan
Aspiration or arthroscopy in theatre
The risk headings are the same as for primary TKR.
The infection and blood clot rate is higher and the functional outcome and survival of the implant is lower. This reflects the increase complexity of the surgery.