Study Reveals What Causes Early Failure of All-Metal Hip Replacements (DrugWatch)
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Numerous studies have linked metal-on-metal hip-replacement systems to dangerous complications and painful consequences. But until now, none pinpointed their failure with as much precision as a study published recently in the Orthopedics medical journal.
Researchers in the July 2012 study found that more than three-fourths of all metal-on-metal hip devices, such as the DePuy ASR and DePuy Pinnacle models, fail within two years of being implanted. Even more shocking, 98 percent of the patients in the study needed revision surgery within three years of the original operation.
Data from 80 patients needing the corrective surgeries was analyzed for the study, and researchers attributed the early failure rates to aseptic acetabular loosening, metal hypersensitivity reactions, pseudotumor formation and component seizing.
Acetabular cup loosening was the most common culprit of early failure rates at 56.25 percent, and researchers described which brands were most often at fault:
“Of the 45 cups that loosened, 35 (78%) were Durom acetabular cups (Zimmer). The second most common cup that experienced aseptic loosening was the ASR cup (DePuy), with 4 (9%) failed cups. The remainder of the cups that loosened were 2 (4.4%) Magnum cups (Biomet), 2 (4.4%) Pinnacle cups (DePuy), 1 (2.2%) Conserve cup (Wright Medical), and 1 (2.2%) unknown cup.”
The physician authors also found evidence to substantiate previous conclusions that all-metal hip-implant devices shed metal shavings when the cup and socket rub against each other. The metal debris has been a cause for concern, with researchers linking it to metallosis, a metal poisoning of the blood and surrounding tissues. One British study even linked the metal particles to an increased risk of kidney and bladder cancers.
In the Orthopedics study, ten (12.5%) of the 80 patients were found to have “significant metallosis or significantly involved local tissue changes due to the metal debris seen during revision surgery.” However, more extensive testing of the tissue by cell count, frozen section and intraoperative cultures came back negative.
Patients involved in the study were between the ages of 31 and 84 years; 41 were men and 39 were women. Race was not an issue. All 80 patients had undergone revision surgery for metal-on-metal hip implants.
DePuy Orthopaedics, a Johnson & Johnson subsidiary that manufactures two of the acetabular cups that were found to have loosened in the study, is facing thousands of lawsuits over its defective ASR and Pinnacle devices. DePuy recalled 93,000 ASR hip implants worldwide in August 2010 because of early failure rates. The Pinnacle is the predecessor to the ASR model, and it still remains on the market today, despite the health risks. The first federal ASR trial could start as soon as March or April 2013, and the first federal Pinnacle trial is scheduled for September 2014.