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Significant increase in failure rates of MoM designs predicted with time
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Given their experience with 121 recalled metal-on-metal hip implants using two designs and the reports of other clinicians on these devices, British investigators predicted that more patients under their care will likely require component revisions after 5 postoperative years.
Of the MoM prostheses in question — the ASR RHA resurfacing and ASR XL modular total hip replacement (both DePuy; Warsaw, Ind.) — 111 implants with 44 months mean follow-up had survived (92%) at the time the devices were recalled in the United Kingdom in 2010, the researchers noted in the study abstract. After the investigators reviewed this cohort, implants in 38 hips met the requirements for additional imaging and blood metal ion testing. Seven of the hips that the authors subsequently reviewed were immediately added to a list of patients set to undergo revision surgery (one ASR RHA and six ASR/XL implants), so that by 1 year after the recall, 23 hip prostheses had been revised (19 ASR/XL and two AXL RHA devices).
The investigators made a diagnosis of an intraoperative adverse reaction to metal debris in all but two of the revised hips at the time of revision.
The researchers reported a current revision rate of 19% for both prostheses at mean follow-up of 62 months for the ASR RHA and 53 months for the ASR/XL prostheses. In addition, there was an 80.8% 5-year cumulative survival rate for the ASR/XL hip replacement components with revision for any reason as the endpoint, according to the abstract.
“Given experience elsewhere we expect this rate may increase significantly with time,” the authors wrote.
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Whitwell GS. Hip Int. 2012. doi:10.5301/hip.2012.9351.
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