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Metal-on-metal hip replacements have experienced an unusually high failure rate, as high as 43% for one model. Several models have been subject to voluntary recalls, and Great Britain’s National Health Service recently announced a ban.
Metal-on-metal hip replacements were introduced under a belief that they would be more durable than other types of implants. However, metal debris—usually chromium or cobalt—can be released into the patient’s body as the implant’s ball and socket rub against each other. This can lead to reactions such as inflammation, groin pain, dead tissue, and bone loss, and often forces patients to have a procedure to replace the implant, known as revision surgery.
The US, UK, Australia and Canada have each issued health warnings related to the failure of metal-on-metal hip replacements.
FDA Hip Replacement Approval Process
The FDA does not require clinical trials for orthopedic implants if the device is similar to one already on the market. This ostensibly allows companies to make incremental changes to their devices without resubmitting them for approval. In the case of DePuy’s ASR (Articular Surface Replacement) XL Acetabular implant, that process allowed an unapproved joint design to be incorporated into a hip replacement and the device released to the market without clinical testing.
A 2013 article in the New England Journal of Medicine neatly illustrates the flaws in the 510(k) approval system by tracing the ancestry of the ASR XL Acetabular hip system.
There were numerous problems with the implant’s approval process:
- Individual aspects of the device design were compared to different predicate devices (known as a split predicate); these specific features had never been used together in a single device.
- Several predicate devices (in a “family tree” of no fewer than 95 devices) were discontinued well before the ASR’s clearance due to high revision rates. However, under the rules of the 510(k) process, DePuy needed only to prove that the ASR was no less safe than those devices–an extremely low standard, since the predicate devices weren’t actually safe to begin with.
- The ASR’s approval could ultimately be traced back to devices that were introduced before the 1976 Medical Device Amendments, which set out modern standards of clinical testing, including the 510(k) system. In other words, no predicate device to the ASR actually received adequate human testing.
In January of 2013, the FDA proposed changes to existing rules that would require approval of new metal-on-metal hip replacements prior to their release.