Revision Knee Replacement
Why Do Knee Replacements Need Revising
Revision Total Knee Replacement (RTKR) is major surgery that involves removing an existing TKR and replacing it with another. Usually, but not always, all the components of the TKR will be revised. A TKR may need to be revised for a number of reasons and clearly understanding the reason why a TKR is not working well is the key to a successful revision. Reasons for revising a TKR include:
Osteolysis. Osteolysis is damage to the bone that the TKR is attached to caused by wear of the plastic bearing. Osteolysis can be very destructive to bone and ligaments and is best treated when first detected. If detection occurs before any implant loosening occurs then the plastic liner is changed for a new one which is quick and simple. If on the other hand there is severe damage to bone and ligaments reconstruction is more difficult. Fortunately, very significant advances in polymer technology over the last 20 years means that currently used plastic bearings are likely to last well and the proportion of revisions due to osteolysis has dropped.
Loosening. Loosening of the implant in the bone used to be synonymous with osteolysis. As improvements in polymer technology have improved the plastic bearings, osteolysis has become much less common. Loosening is now more commonly due to failure of bone rather than the implants and is related to obesity and osteoporosis. This is therefore more of a problem in women who are prone to osteoporosis after menopause. Staying lean and managing your bone mass is the key to avoid a revision.
Infection. Infection is very difficult to successfully treat around a foreign body (a TKR is a large foreign body). In ideal circumstances an infection can be treated successfully without removing the implants but outside of ideal circumstances the quickest and most reliable way to cure the infection is to remove the TKR. A new but temporary TKR is implanted. A definitive revision as a second stage procedure will often be required once all evidence indicates the infection is eradicated. An infected TKR is an awful thing. This is why the primary implant should be undertaken in optimally prepared patients.
Instability. Giving way or a feeling of insecurity can have several causes and understanding the exact nature of the instability is the key to a successful revision. Revision TKRs can have constraint built into them to compensate for ligament problems but as a rule the least constrained knee replacement that will do the job will last longest.
Stiffness. Once again, the key is understanding why the first TKR became stiff. Worthwhile results can be obtained when revising for stiffness particularly if a clear mechanical cause for the stiffness is indentified.
Patellar Resurfacing: Not all surgeons resurface the kneecap routinely when doing a TKR. There are pros and cons to patellar replacement and the profession has been arguing about patellar resurfacing for 30 years. The fact of the matter is that a small proportion of unresurfaced patellae will continue to cause pain and a second operation will be needed to resurface the patella only. Dr McEwen routinely resurfaces the patella.
How does a revision differ from primary
Revision TKR differs from primary TKR in several ways. More tests are required before surgery to clearly identify the reason for failure and to quantify the extent of damage to the bone around the knee. Surgical access is more difficult so a longer incision is often necessary. Bone loss and ligament damage needs to be dealt with in a way that allows immediate stability, weight bearing and unrestricted movement. Antibiotics are more potent and used for longer. Time in hospital is a day or two longer. Otherwise the process of having a revision TKR is very similar to a primary TKR. This process is described in detail in the Total Knee Replacement document in this section.