Similar to a total hip replacement, there are a number of reasons why a total knee replacement may fail, some of which are more common than others. These can include:

• Infection
  
  
• Instability – If the muscle and ligament tension around the total knee replacement is not sufficient, or the components are unable to be placed in the optimum positions during surgery, this may lead to repeated dislocations of the patella or even dislocation of the tibia on the femur. Fortunately these are both very rare. More commonly, the instability may be experienced as a sense of “inability to trust the knee”, especially on uneven or inclined surfaces or when descending stairs. This may be an extremely debilitating situation and may be difficult to treat in some cases.
  
  
• Wearing out of the tibial liner - due to multiple millions of repeated movements of the total knee replacement. This results in microscopic amounts of the surfaces of the moving parts being worn away and shed into the surrounding tissues as “wear debris” which can result in…
  
  
• Osteolysis – bone destruction around the knee joint. This occurs as a consequence of the human body’s defensive inflammatory response to microscopic particles released as wear debris from the moving surfaces of the total knee replacement
  
  
• (Aseptic) Loosening – where either the femoral or tibial component fails to develop an intimate bond with the bone that it’s been implanted in, leading to small movements of these components within the bone.
  
  
• Breakage of the components – can be considered an extreme form of wear in the case of a broken tibial liner or tibial tray.

When these problems are detected, either due to the development of symptoms or as diagnosed on routine follow-up X-rays, then a revision of the total knee replacement needs to be considered. This is a major orthopaedic procedure and involves removing the old prosthesis and any unhealthy bone, and then using new components that are anchored into/onto the bone further afield compared to the initial total knee replacement. Usually this means adding devices such as rods that pass from the revision femoral and tibial components into the bone marrow of the femur and tibia to improve their grip in the bone.

In some instances, e.g. severe instability, not only do the implants need to be more firmly anchored in/on the host bone, but they may also need to be linked to each other by a specific hinge mechanism or similar. This allows most movement but is usually stiffer than beforehand, and because of the degree of constraint, tends to cause more problems over time with loss of fixation on the bone.

The likely outcomes from a revision of a total knee replacement depends on the reason for the revision itself and overall are probably less predictable than that seen in primary total knee replacement.