How To Define Success of a Total Knee ReplacementMore and more younger adults (less than 60 years old) are getting total knee replacements (TKRs). Severe, disabling pain from degenerative joint disease is the main reason given for this type of surgery. And early reports indicate great success so far -- a survival rate of the implant that was 82.2 percent for the first 15 years.
But is that survival rate really accurate? Is the whole picture being seen here? Dr. Andrew J. Price and associates conducted a study with much less favorable outcomes. The reason for the difference is the type of measurement used to define success.
Most surgeons use revision as the end-point of the implant's life. Infection and loosening are the usual reasons an implant must be revised, removed, or replaced. But that's a surgeon's idea of failure. Patients are more likely to use pain as a gauge of success vs. failure.
And the results of Dr. Price's study showed that most patients report at least moderate pain in the years following knee joint replacement. They aren't pain free after all. Using revision OR pain as a criteria for the endpoint in implant survival, the rates fell to less than 60 per cent.
Dr. Price points out that revision (for any reason, not just infection or loosening) and pain are just two variables that can be used as an end-point in determining success versus failure of implants. There are others as well. For example, function such as walking, going up or down stairs, getting up and down off the floor, and even running could be used as measures of outcome in younger patients.
One reason revision rates are used as the final data on long-term survival of total knee replacements in younger patients is because there are so many other possible factors that can get in the way of gathering good data. The patient may have other health care problems referred to as comorbidities that could influence the results.
Other questions come up. For example, what cut-off date should be used during the follow-up? If using function as a potential endpoint in outcome, do we need preoperative assessment of function to show before and after results? Most tests of function do require before and after measurements in order to calculate the relative change in function.
That begs the question of which test to use to assess function. Dr. Price and his group of researchers used the Oxford Knee Score (OKS). The OKS is a self-reported pain measure. Patients rate their pain from zero (no pain) up to 48 (maximum pain). It isn't really a test of function.
The researchers concluded that more study is needed to gather data on younger patients getting total knee replacements. Using only one measure of outcomes (revision) may not provide all the necessary information needed to determine the success rate of total knee replacements in this age group. This means the current reported outcomes of total knee replacements in younger patients may be too optimistic.
Pollack P. TKA Outcomes in Younger Patients: Too Optimistic? In AAOS Now. March 2009. Vol. 3. No. 3. Pp. 9.
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