The 510(k) ancestry of a metal-on-metal hip implant.

n engl j med 368;2 nejm.org january 10, 2013 97 pathway that is not intended for evaluating safety and effective­ ness. This pathway, called the 510(k) process, instead involves evaluation of “substantial equiva­ lence” to previously cleared de­ vices, many of which have never been assessed for safety and ef­ fectiveness and some of which are no longer in use because of poor clinical performance. The Medical Device Amend­ ments of 1976 created three classes of devices: class I in­ cluded low­risk devices, such as toothbrushes; class II contained moderate­risk devices, such as infusion pumps; and class III included high­risk devices and those awaiting proper classifica­ tion, such as metal­on­metal hip implants. These classes roughly corresponded to the level of pre­ marketing review required. Thus, class I and II devices underwent review for substantial equiva­ lence to devices already on the market, also called preamend­ ment devices (although subse­ quent legislation granted ex­ emptions). Class III devices were meant to undergo the more rig­ orous premarket approval (PMA), the only pathway that re­ quires clinical data. However, class III devices were allowed to receive review for substantial equivalence temporarily, until the FDA down­classified these devices or promulgated regula­ tions requiring PMA. Congress had always intended class III de­ vices 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.1 As of December 19, 2012, how­ ever, the FDA still had not com­ pleted this transition to PMA for high­risk devices, although it had stated its intention to clear pro­ posed rules for all remaining class III preamendment devices by December 31, 2012.2 Current­ ly, 19 different types of class III devices, including metal­on­metal hip implants, are allowed to reach patients through 510(k) clearance. Because of this loophole, compa­ nies 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 substantial­ ly equivalent to even earlier de­ vices, and so on, all the way back to preamendment devices. Be­ The 510(k) Ancestry of a Metal-on-Metal Hip Implant