Newer doesn t always mean better. At least that s the conclusion of a review published in The Journal of Bone and Joint Surgery, which finds that newer hip and knee replacement designs (such as metal-on-metal hips) introduced from 2003 through 2007 are not any more durable than older models (largely comprised of metal and plastic).
For the study, researchers collected data on implants from Australia s orthopedic registry; their results indicated that, on average, new artificial knee and hip replacements were 30 percent less effective than older versions. However, as ACSH s Dr. Gilbert Ross points out, such statistics can be misleading, since these are just averages. To find that newer implants are no better than older ones is a disappointment, for sure, he says. But saying they fared 30 percent worse is almost meaningless from a statistical point of view, since whatever the average durability is, some significant fraction is bound to be less durable just as some will be more so.
Although about 700,000 Americans undergo hip or knee replacements annually, the U.S. doesn t keep a registry of data on these patients. As the recently published Australian review observes, registry findings are sometimes at odds with results from published studies that accompany the introduction of new implants, because these initial studies are often short-term. But as Dr. Ross says, This is the same thing we see with clinical drug trials, in that the results of these trials are sometimes invalid once a medication is in wide circulation. That s why we have Phase IV post-market analyses to help determine whether something is as safe and effective as smaller early-phase trials led us to believe.