Writing in the New England Journal of Medicine, the researchers say that a “clinical trial might have highlighted the high revision rate…which became evident after nine months when it was compared with all other total conventional hip prostheses in the Australian Joint Registry…and which precipitously worsened over time.”

The company 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 (about 13%) reported by the National Joint Registry for England and Wales.

The researchers traced the device’s ancestry back more than five decades through a total of 95 different devices, including 15 different femoral heads and sleeves and 52 different acetabular components. They report that the 510(k) clearance for the ASR XL focused on three characteristics: the porous bone ingrowth surface, metal-on-metal articulation, and femoral head sizes that were larger than those of the predicate total hip prostheses.

“These three characteristics were uniquely combined in the ASR XL, but were evaluated for ‘substantial equivalence’ by comparing select characteristics to different predicate devices, none of which contained all of these characteristics,” the report says.

Thus, the porous bone ingrowth surface was not specific to the type of articulation and in most cases the predicates were not metal-on-metal and were substantially different in design from the DePuy unit.

CDRH clearance of the metal-on-metal articulation was based on a much smaller group of predicates, some of which differed substantially in design from the ASR XL or had poor clinical performance. Ultimately, the researchers found, clearance was based on the claim that the predicate devices were substantially equivalent to three prostheses that were used before 1976 and which were discontinued because of their high revision rates long before the ASR XL was cleared.
“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,” the researchers conclude.

“The recently passed Medical Device User Fee and Modernization Act contains a provision that should make it easier for FDA to close the loophole for the remaining 19 Class 3 devices by allowing the agency to reclassify devices by order rather than through regulation. There would be value in an FDA-sanctioned registry.”

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