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Jan 11 2013

Ancestry of a Metal-on-Metal Hip Implant And Metal Shearing Issue

Posted in Community Service, Nursing Home, Product Liability
Medical devices, improperly manufactured and designed, that are allowed to bypass the standard pathway for testing and approval, may inadvertently cause extensive injury or death to the patient, says Alabama liability attorney Keith T. Belt . 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. 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.1 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. The use of larger heads was an important characteristic of the ASR XL. The clearance for the large metal heads with sleeves was based in part on predicates that were not used in total hip replacement but were designed for use in partial hip replacement, in which the large metal heads articulate with the natural articular cartilage of the acetabulum, not with a metal cup. This ancestry reveals serious flaws in the 510(k) procedure for metal-on-metal hips, which resulted in clearance of a new device that was never shown to be safe and effective. A clinical trial might have identified the high revision rate of the ASR, which became evident after 9 months when it was compared with all other total conventional hip prostheses in the Australian Joint Registry (9-month-to-1-year hazard ratio, adjusted for age and sex, 2.62 [95% confidence interval, 1.67 to 4.11]) and which precipitously worsened over time.5 As thousands of Americans are painfully learning, there are unknown risks with devices that enter the market without clinical data showing safety and effectiveness, and implanted body parts cannot be recalled as easily as defective auto parts. For Additional Information:   About Belt & Bruner, P.C.