Revision on a Knee Replacement

A revision knee replacement surgery is a procedure that is performed to replace a knee implant that is no longer functioning properly. Knee replacement implants are designed to last a long time, but they do not last forever, and there are a number of problems that can occur necessitating a repeat surgery to replace the implant.

Revision knee replacement is a major surgery because performing a replacement surgery can be much more complicated the second (or third, or fourth...) time in the joint. Over time, scar tissue, bone loss and instability can all contribute to making a repeat surgery a much more difficult treatment.

Most knee replacements last several decades, some longer. However, there are also times when a knee replacement needs to be redone after years or even just months. Understanding why a knee replacement has worn out is critical to performing a successful revision knee replacement.

The average knee replacement lasts more than two decades, but there are reports of implants lasting longer, and new materials and surgical techniques are hoped to provide even longer-lasting knee replacements. That said, there are times when knee replacements may last a very short time, even in otherwise healthy patients. A small percentage of patients (around 1-2%) ends up needing their knee replacement revised within a few years of their initial surgery.

Revision replacements are performed for a number of reasons. Some of the more common include:

• Loosening of the implant
• Infection of the joint
• Instability of the knee
• Malalignment of the parts

Many people ultimately have a revision knee replacement because the problem is causing significant pain. While pain can be a problem in itself, a revision knee replacement surgery should not be performed without understanding why the pain is occurring. Performing this type of surgery for pain without an identified cause is unlikely to yield good results. Instead, the cause of the problem with the knee replacement needs to be precisely understood, and there needs to be a plan to address that problem with the implant. An operation without a clear plan to address the problem is unlikely to be helpful.

Most knee replacements are made with metal caps that cover the end of the thigh bone and the top of the shin bone. Between these metal caps is a piece of plastic that provides a smooth surface for bending of the implant. The plastic can wear out over time, either as a slow, gradual wearing away, or a sudden catastrophic failure.

There are some situations where the wearing out can be accelerated. These situations include when the alignment of the implants was not ideal, when the knee is unstable (too loose), or if the patient performs activities that put too much stress on the implant. Knowing which activities can cause damage to knee replacement implants can help ensure the parts last as long as possible.

Revision replacement is difficult for several reasons. First, when someone has surgery, scar tissue develops, and soft tissues become less identifiable. Performing the second surgery is always more difficult. Second, when performing a knee replacement, bone is removed. When performing a revision knee, often more bone has to be removed, and some may be lost as a result of the problem with the implant. Maintaining adequate bone to support the new implant can be a challenge. Finally, obtaining a knee that is flexible enough to allow for motion, yet stable enough to keep you steady, is also more difficult in revision situations.

The results of revision knee replacement are less favorable than with a first replacement surgery. That said, the results are quite variable, as some problems that require a second surgery are much more straightforward to manage, and others very complex.

The problem with trying to compare results of revision knee replacement is that the reasons to perform the surgery, and the extent of the surgical procedure, is so variable that it is hard to draw conclusions on the data. However, most studies of revision knee replacement showed improved function in most patients (80% or more).