One of the largest medical device scandals in the last decade has involved metal-on-metal hip implants, so-named because of the metal (usually chromium) attachment that attaches a leg to a metal socket.
In the wake of their failures, the US Food and Drug Administration (FDA) moved to examine its regulatory processes, eventually deciding to require premarket approval (PMA) applications for all such implants. But now evidence has emerged that the agency still has further questions about what more it could have done to prevent the devices from ever having reached the market.
Medical devices are a relatively recent addition to FDA's regulatory authority, with FDA only receiving the authority to vigorously regulate them in 1976 under the Medical Device Amendments. Because some medical devices were already marketed at that time, FDA classified them all as class III, high-risk medical devices until it could review and classify them properly.
Some of those devices went on to serve as predicates for 510(k) premarket notification applications, which claimed that they were substantially equivalent to already-approved devices and were thus able to avoid conducting clinical trials to re-prove their safety and efficacy.
The problem with that, some researchers claim, is that many of the original devices which metal-on-metal hips claimed to be ancestors of have since been recalled from the market under dubious circumstances, meaning the devices might never have been safe to begin with. Further, the metal-on-metal hips were not so similar to the original device as to be clearly substantially equivalent. Devices of this sort are routinely approved and are referred to as "split predicates."
In light of those concerns-and a lack of action on the part of Congress during the 2012 passage of the Food and Drug Administration Safety and Innovation Act to explicitly close the so-called loophole-FDA announced on 17 January 2013 that it would move to require all metal-on-metal implant devices to be submitted in the form of a PMA or PDP, which typically require clinical trials in support of the application and thus an investigational device exemption (IDE) application as well.
A New Study
But even with these new requirements, FDA said it is still concerned about hip implants in general, and most especially with respect to how they are worn down. In the case of metal-on-metal hips, the chromium coatings of the device wore each other down, in some cases dislodging metal chromium shavings that caused tissue damage and raised fears about metal ions entering the bloodstream and causing cancer.
In a solicitation notice posted on the Federal Business Opportunities (FBO) website, FDA noted that "there is renewed concern of wear and corrosion of conical head/stem taper junctions in modern modular total hip replacements." While not a "new phenomenon," FDA said new design changes like metal-on-metal bearings, larger femoral heads and modular designs have reintroduced the issue even as the new features more closely approximate patient features.
As a result, FDA said it's embarking on a new project to "investigate the potential link between volumetric wear and corrosion of conical head/stem taper junctions in explanted total hip replacements and clinical outcomes."
As with nearly all solicitation notices, it's looking to the private sector to help it design and run the study, the results of which will be used to "aid development of standard test methodologies for preclinical evaluation of total hip implants."
The study will reportedly look at 250 explanted metal-on-metal hip replacements of various sizes and genders and use the American Society for Testing and Materials (ASTM) protocol for corrosion testing to analyze them. "De-identified patient data and radiographs must be available or obtainable for all devices," the notice explains.
The end goal of the project, which should take about two years total to conduct, is to generate a peer-reviewed journal article explaining correlations between wear and corrosion and relevant parameters (e.g. implantation time, lateral offset, head size, materials, and modularity).
Solicitations are due to FDA by 1 August 2013.