The FDA will discuss these issues at a two-day expert advisory panel meeting on June 27-28, 2012. The discussions will cover two categories of the MoM systems:
1. Metal-on-metal total hip replacement systems consisting of a metal ball (femoral head), a metal femoral stem in the thighbone, and a metal cup in the hip bone (acetabular component).
2. Metal-on-metal hip resurfacing systems consisting of a trimmed femoral head capped with a metal covering and a metal cup in the hip bone (acetabular component).
In May 2011, the agency issued an order for manufacturers of MoM hip systems to conduct post-market surveillance studies to collect more safety data on these devices, including data related to metal ion concentrations in the bloodstream.
The agency is currently considering whether to make MoM hip systems subject to more rigorous testing and premarket review requirements.
DePuy Orthopaedics withdrew its ASR XL Acetabular metal-on-metal DePuy ASR hip replacement on August 24, 2010 following approximately 300 complaints from people undergoing hip replacement. The ASR hip replacement is a metal-on-metal device believed to have a design flaw that has resulted in many patients needing follow-up hip revision surgery to replace the device soon after implant. The ASR is considered by a number of orthopedic experts to be a defective product and DePuy hip replacement lawsuits are currently pending.
A recent study noting an increased failure rate related to those systems that utilize large-diameter femoral heads has added to the FDA's existing concerns over the safety of MoM hip systems.
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Meanwhile, a report by the National Joint Registry for England and Wales (09/11) found that the failure rate of all-metal hips is increasing, with the ASR failing at the highest rate. According to the report, the ASR failed in approximately one-third of patients who were followed for the longest period. The report noted that of people who received the ASR six years ago, approximately 30 percent had it replaced. Of those who had the ASR implanted five years ago, 17 percent had it replaced, although that percentage could increase in the next year.