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Metal-on-Metal Hip Implant Research Provides Few Treatment Cues

Feb 16, 2012 | Parker Waichman LLP

Exactly how should revision surgeries for recipients of metal-on-metal hip implants be approached?  Should the painful procedures be reserved for all-metal hip replacement patients who exhibit obvious signs of failure, such as pain or difficulty walking?  Or should patients undergo revisions if they test positive for high levels of cobalt or chromium ions in their blood, whether or not they have symptoms of implant failure?

It is believed that metal-on-metal hip implants can shed dangerous amounts of cobalt and chromium through wear, leading to tissue damage, premature device failure, the need for revision surgery, and even long-term health problems, including heart and nervous system damage.  So far, two all metal hip implants,  DePuy Orthopaedics’ ASR Hip Resurfacing System and the DePuy ASR Acetabular System, have been linked to an unusually high early failure rate, and recalled because of these concerns.  A third, an all-metal version of DePuy’s  Pinnacle hip replacement device,  has been named in hundreds of U.S. lawsuits alleging it is similar in design to the ASR implants, causes similar problems,  and should have been recalled as well.

Last May, the U.S. Food & Drug Administration (FDA) directed 21 makers of all-metal hip implants, including DePuy, to conduct post-market studies of their products to determine if they were shedding dangerous amounts of metallic debris in patients. 

Apparently, there is no consensus among researchers and doctors about the treatment of metal-on-metal hip implant studies.  In fact, studies of metal-on-metal implant recipients have return conflicting results when it comes to this issue.  In 2010, British regulators did warn patients there to have their blood tested.  In cases where chromium or cobalt levels were 7 ppb or higher, they said imaging studies were warranted.   If those also indicate abnormalities, then revision should be considered.   In the U.S., however, the FDA has not issued any advice on blood testing.

Last week, at the  American Academy of Orthopedic Surgeons' (AAOS) annual meeting, Joshua Jacobs, MD, a prominent researcher with Rush University in Chicago, said at a press briefing said that no single factor should determine whether a given patient should have a metal-on-metal implant removed.

"If a patient is symptomatic, they have a high-risk device, they have high metal ion levels, and maybe on x-ray ... they show bone loss or on an MRI scan some soft tissue swelling, a so-called pseudotumor, that's someone where I think you'd want to consider revision," he said according to a report from MedPage Today. 

On study presented by British researchers at last week's AAOS conference indicated that serum chromium or cobalt ion levels of 7 ppb should trigger a discussion about immediate revision surgery.  But another study presented moments earlier by a U.S. physician found no relationship between ion levels and tissue damage seen in metal-on-metal implant recipients who had revisions. Yet other research found that while removal of metal-on-metal implants leads to swift and steep declines in serum or whole blood ion levels, they often remain abnormally high for years afterward.

Yet another study, conducted by researchers at Imperial College London, indicated that a lack of symptoms does not indicate that metal-on-metal hip implant patients are in the clear.  The research focused on the presence of pseudotumors, an indicator of serious soft-tissue damage, in people ceramic-on-ceramic and metal-on-metal hip implants.  None of the patients studied exhibited any symptoms typical of failure, and problems were not clinically suspected in any of them.  Yet despite an apparent absence of problems, MRI scans showed that 16 of 28 metal-on-metal recipients had pseudotumors, versus one of 15 patients with ceramic-on-ceramic implants.



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