Patients with Metal Hip Implants May Want to Consider Regular Blood Tests
A recent study published in the British Medical Journal Open reported that an elevated level of cobalt in the blood was an important risk factor for future hip implant failure. Researchers examined patients who had been implanted with metal-on-metal (MoM) hip devices, like the recalled DePuy ASR and the Smith & Nephew Birmingham. These implants and other MoM devices like them have been linked with complications like tissue damage, bone loss, and swelling, all of which can lead to premature loosening and revision surgery.
While the FDA currently recommends against routine blood metal ion testing in patients who are suffering no symptoms, the authors of this study suggested the organization rethink that recommendation.
Study Results Show Cobalt Matters
For the study, researchers reviewed blood metal ion screening data and outcomes for 278 patients who had gone through hip resurfacing, a bone-saving procedure similar to a total hip replacement.
Researchers then looked at the seven-year risk of failure with the implants, compared to blood levels of cobalt. The results showed:
- Male patients with 10 mcg/L cobalt had nearly a 22 percent higher risk of failure with the DePuy ASR, and a 2.6 percent higher risk with the Smith & Nephew Birmingham
- Female patients with 10 mcg/L cobalt had nearly a 43 percent higher risk of failure with the DePuy ASR and a nearly 6 percent increased risk with the Smith & Nephew Birmingham
Overall, patients with 10 or more mcg/L of cobalt were more likely to experience implant failure seven years after the initial implantation than patients who had lower levels of cobalt in their blood.
Regular Blood Tests Suggested
Though this particular study didn’t examine other types of MoM hip implants, such as the Zimmer Durom Cup or the Stryker Rejuvenate, the researchers noted this limitation and suggested further studies, as the results may apply to these implants as well.
At this point, the authors stopped short of recommending regular blood tests for those with total hip replacements, but did suggest that those who have gone through hip resurfacings with MoM products keep an eye on their blood.
“Ion concentrations, if low,” the authors wrote, “can be reassuring to both patients and surgeons and can also allow rationalization of resources. Grossly elevated ion concentrations indicate the risk of early prosthetic failure and can be used to direct further investigations or implement closer follow-up.”
Companies Facing Hip Lawsuits
DePuy Orthopaedics and parent company Johnson & Johnson implemented a voluntary product recall in August 2010, withdrawing the DePuy ASR from the market. The first of over 10,000 lawsuits against the companies resulted in an $8.34 million verdict for the plaintiff.
Stryker also recalled the Rejuvenate and ABG II systems in July 2012, citing concerns about fretting and corrosion. Though MoM implants were initially marketed to be more durable and better suited to younger, more active patients, post-marketing reports and studies indicated they created additional complications and were more likely to fail prematurely than implants made of combination ingredients.
In January 2013, the FDA issued a safety communication on MoM hip implants, stating that the have “unique risks in addition to the general risks of all hip implants.” They have proposed new regulations that would require manufacturers to test for safety and effectiveness prior to market launch.
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