A study by Hospital for Special Surgery researchers has provided the first comprehensive look at just how metal-on-metal total hip replacements are failing in patients around the country. Made possible by what is thought to be the largest archive of failed joint replacements, the research should help doctors develop a better hip replacement for future patients. The study will be reported at the upcoming annual meeting of the American Academy of Orthopaedic Surgeons, Feb. 7-11.
"This paper is the first step in what is a path to try to understand what the problems are with metal-on-metal joints," said Timothy Wright, Ph.D., Kirby Chair of Orthopedic Biomechanics at Hospital for Special Surgery (HSS). He said that information gleaned from the study should be useful in improving metal-polyethylene implants, the most common hip implant put in patients today.
"We still use metal implants. We may rub them against polyethylene instead of against another metal, but anything we can learn about these mechanisms of damage could be important," he said. He also pointed out that evidence suggests that the physical structure of the implant might play a role in the failed metal-on-metal implants and not the metal itself. In recent years, advances in the materials have allowed implants with bigger heads to be used, which increases stability, but now evidence suggests this may cause other problems.
"What we learn about the effect of head size and learn about the effect of positioning these components, and certainly what we learn about the biologic reaction to metallic debris is going to help us understand problems in general with total joint replacements," said Dr. Wright. "It's not enough to say, because some metal-on-metal implants have adverse reactions, it has got to be all about the metal and let's just condemn an entire technology. We need to understand, in a systematic way, what is going on."
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Hospital for Special Surgery