Elizabeth Hofheinz, M.P.H., M.Ed. • Thu, April 17th, 2014
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“The data proves that registries cannot compare implant designs!” says David Murray. “Going to single surgeon or institutional efforts allow large numbers of patients to be studied very quickly,” says David Lewallen. “What registry studies really do is allow us to ask interesting questions and perhaps direct the next studies.”
This week’s Orthopaedic Crossfire® debate is “The Stuff of Implant Registries: Of Limited Value.” For the proposition is David Murray, M.D., F.R.C.S. from Nuffield Orthopaedic Centre in Oxford, UK; against the proposition is David G. Lewallen, M.D. from Mayo Clinic in Rochester, Minnesota. Moderating is Robert T. Trousdale, M.D. from Mayo Clinic in Rochester.
Mr. Murray: “Registries exist for three main reasons: to compare different types of joint replacement, to compare implant designs, and to provide an early warning for poor implant designs. The primary endpoint for these comparisons is revision.”
“How reliable is this information? I’ll give some examples from unicompartmental knee replacement. Data from a regional registry in the UK—the Trent Registry—showed 10 different total knees followed out to 15 years. Not surprisingly, most would have a survival rate of 90% at 15 years. But there is an implant with 100% survival at 15 years. Everyone who believes in registries says that is the implant you must use. It is the Sheehan Knee…a fixed hinge. I asked the people organizing why this device has a 100% survival and they said, ‘Oh well, that’s because you can’t revise it.’ So, ease or difficulty of revision is perhaps the single biggest determinant of the revision rate. In other words, what matters is the threshold for revision.”
“One of the few things that all the registries agree on is that unis have a higher revision rate than totals. On the basis of this they conclude that unis have poorer results. Therefore they tell surgeons not to do unis. But is the higher revision rate because unis have poorer results, or might it be to do with thresholds? Imagine two patients come to see you in clinic. Both say they have pain worse after the operation than before, and neither has any mechanical problem. I say that if the patient had had a uni, that many of you would revise it because it’s easy; whereas if they’d had a total knee most surgeons wouldn’t because the results would be poor.”
“The New Zealand Registry also gets outcome scores. Not surprisingly, the unis have slightly better scores than totals. What’s interesting is that in New Zealand they subdivide the outcome scores into whether they’re poor, fair, good or excellent. Unis have more ‘excellent’ results, but what is surprising is that unis have less ‘poor’ results than totals. So the difference in revision rate is not because of poor results. Might it be to do with this threshold?”
“The New Zealand Registry also compares the postop Oxford Score with the subsequent revision rate. Patients with an outcome score of less than 20—worse postop than preop—have a high revision rate. What this registry does not draw attention to is that the axes are different. If you plot these graphs on the same axis you see they are hugely different. If you have a total knee with a very bad outcome, 10% are revised; if you have a uni with a similarly bad outcome, 60% are revised. In other words, the difference in revision rate is a manifestation of a different threshold for revision.”
Read the rest here – RY Ortho
