Sunday, February 11, 2018

How safe are FDA-cleared joint implants?

The 510(k) Ancestry of a Metal-on-Metal Hip Implant

This article from the New England Journal of Medicine contains an important perspective on the FDA clearance process for orthopaedic devices. The following paragraphs are critical reading for those concerned about implant safety:

"Many medical devices that pose great safety risks to Americans, including metal-on-metal hip implants, currently enter the U.S. market through a Food and Drug Administration (FDA) regulatory pathway that is not intended for evaluating safety and effectiveness. This pathway, called the 510(k) process, instead involves evaluation of “substantial equivalence” to previously cleared devices, many of which have never been assessed for safety and effectiveness and some of which are no longer in use because of poor clinical performance.

The Medical Device Amendments of 1976 created three classes of devices: class I included low-risk devices, such as toothbrushes; class II contained moderate-risk devices, such as infusion pumps; and class III included high-risk devices and those awaiting proper classification, such as metal-on-metal hip implants. These classes roughly corresponded to the level of premarketing review required. Thus, class I and II devices underwent review for substantial equivalence to devices already on the market, also called preamendment devices (although subsequent legislation granted exemptions). Class III devices were meant to undergo the more rigorous premarket approval (PMA), the only pathway that requires clinical data. However, class III devices were allowed to receive review for substantial equivalence temporarily, until the FDA down-classified these devices or promulgated regulations requiring PMA. Congress had always intended class III devices to undergo PMA, and in 1990, it directed the agency to establish a schedule to finish the transition to PMAs for all devices that were to remain in class III.

As of December 19, 2012, however, the FDA still had not completed this transition to PMA for high-risk devices, although it had stated its intention to clear proposed rules for all remaining class III preamendment devices by December 31, 2012. Currently, 19 different types of class III devices, including metal-on-metal hip implants, are allowed to reach patients through 510(k) clearance. Because of this loophole, companies that market these devices are often legally able to obtain clearance without demonstrating safety and effectiveness through clinical studies, but by claiming substantial equivalence to earlier “predicate devices” — or pieces of those devices — which may also have been found substantially equivalent to even earlier devices, and so on, all the way back to preamendment devices. Because many predicates have never been assessed for safety and effectiveness, an FDA finding of substantial equivalence does not mean that a new device is safe and effective; it means only that the device is deemed no less safe and no less effective than a predicate.1 Even voluntarily recalled devices can serve as predicates, as long as the FDA did not formally remove these devices from the market or a court did not find them adulterated or misbranded.

One prominent type of class III device that remains eligible for 510(k) clearance is metal-on-metal hip implants, such as the DePuy ASR XL Acetabular Cup System, which received FDA clearance in July 2008 without a clinical study. The Australian Orthopaedic Association National Joint Replacement Registry initially reported in September 2008 that this device required revision surgery at a high rate, and in 2010 the National Joint Registry (NJR) for England and Wales reported a 5-year revision rate of approximately 13%, which was more than four times the registry's reported 5-year revision rate for all hip-replacement prostheses combined. DePuy voluntarily recalled the ASR XL in Australia in 2009, citing “declining demand” as a reason, and then worldwide in 2010 because of the high revision rate reported by the NJR.

Using FDA documents obtained from the agency's database and Freedom of Information Office, we traced the ancestry of the ASR XL back more than five decades, through a total of 95 different devices (including femoral stems), including 15 different femoral heads and sleeves and 52 different acetabular components (see figure).

The point here is that the 510(k) clearance process does not provide assurance that a device is either safe or effective. It only states that it is "substantially equivalent" to a prior legally marketed device (even if that device had been been withdrawn from the market by the company because of safety concerns (see this link).

By contrast, premarket approval (PMA) is the FDA process of scientific and regulatory review to evaluate the safety and effectiveness of Class III medical devices. Class III is the most scientifically rigorous classification of medical devices and encompasses most of the orthopedic implants on the market today (see this link).

It is worthwhile understanding the difference between these two FDA mechanisms.

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