When our clients discover that their metal-on-metal (MoM) hip has failed and never went through U.S. Food and Drug Administration (FDA) approval for safety and efficacy, they ask – how did that happen?

Most Americans do not understand that medical devices are largely unregulated, even for those devices that are intended to be permanently implanted in the body. The FDA just does not have the personnel or the funding to oversee medical devices the way it does drugs.

This month in the New England Journal of Medicine a Perspective piece “The 510(k) Ancestry of a Metal-on-Metal Hip Implant,” lays out exactly what happened.

The Medical Device Amendments of 1976 determined that medical devices fell into one of three classes – Class I for low-risk devices such as band aids and toothbrushes; Class II for moderate-risk devices such as an infusion pump; and Class III was reserved for high-risk devices and some that never were classified such as metal-on-metal hips.

The classes don’t always represent the level of risk. For example, transvaginal mesh is considered Class II even though it is a permanent implant.

For the low or moderate risk devices it would be adequate to name a “substantial equivalent” device that was already being sold. That is the 510(k) notification process for FDA approval. The device maker essentially notifies the regulatory agency it plans to market a device and with an exchange of paperwork names a “predicate” even though that predicate may never have undergone any stringent reviews for safety.

Class III devices, those high-risk were supposed to undergo a more careful review requiring clinical trials such as what drugs undergo. That’s called the premarket approval (PMA).

MoM hips fall into a sort of limbo.

Although Class III, they are allowed to be approved under 510(k). They were supposed to be reclassified by December 31, 2012 however the watchdog agency failed to meet its deadline. Nineteen Class III devices including MoM hips can still be marketed through a 510(k) clearance.

“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,” said Brenda Fulmer, a Partner at Searcy Denney who oversees MoM cases at the firm.

Consider this – even a device that has been recalled can serve as a predicate! That is something most people would find astonishing and unacceptable. It’s not what we expect of taxpayer supported regulatory agencies.

The DePuy ASR XL Acetabular Cup System- a MoM hip implant received 510(k) clearance in June 2008. There were no clinical studies required even though the elements that made up the MoM hip were never before used together.

The 510(k) process does not take into consideration new devices, new design, new materials, and new technology. The ASR has a porous bone in-growth surface, metal-on-metal components, and a large femoral head that was novel. The researchers say none of the predicates named had the same combination of characteristics.

Looking forward, the authors say the recently passed Medical Device User Fee and Modernization Act should make it easier to reclassify those 19 devices still in limbo by either requiring a more stringent PMA review or reclassify them as Class II.