Langton says he is "not so concerned about gross hip failures. I am very concerned about the theoretical risks that these blood levels may lead to."
He adds that in the UK, which has the benefit of a hip surgery registry that the United States lacks, problems have shown up with the other devices too. "We do not believe this is a problem specific to DePuy," he wrote. "I have seen similar failures with most of the other manufacturers' hips, too," he says.
In May 2011, the FDA issued 145 orders for post-market surveillance to 21 manufacturers of MoM total hip systems to develop a research protocol that addresses these complaints. Manufacturers, who are responsible for funding these studies, should track patients for eight years after surgery, conduct a failure analysis.
But in a New England Journal of Medicinearticle published Thursday, Joshua Rising, MD, Ian Reynolds and Art Sedrakyan, MD, of the Medical Device Initiative of the Pew Health group, lamented not only that these studies are taking a long time to start, they may never produce meaningful information.
Three weeks ago, "the FDA and manufacturers had reached agreements on study protocols for less than one quarter of the devices, most of the study plans had not been finalized, and it was unclear whether any studies had begun. Moreover, methodologic issues will limit the usefulness of the information that emerges from these studies," they wrote.
"One significant shortcoming (of FDA's order) is that each manufacturer is permitted to conduct its own independent study on its product or products," they wrote. "The resulting lack of harmonization among studies will lead to challenges in pooling data and making cross-product comparisons."
Companies may measure chromium and cobalt levels differently and introduce "uncertainty into attempts to pool results."
The authors advise the FDA to use "warning letters, fines, and removal from the marketplace to demonstrate its commitment to post-market surveillance.
"While the FDA and other stakeholders struggle with these systemic issues, the problems with metal-on-metal hip implants will continue to occupy the agency, clinicians, manufacturers, and thousands of affected patients for the foreseeable future."
Some aren't sure the problem is that extensive. Stephen Kantor, MD, an orthopedist with a high-volume hip surgery practice at Dartmouth-Hitchcock Medical Center in Lebanon, NH, doubts that the problems with MoM devices approaches that many patients. At his hospital, patients have normal blood work and feel fine.
And he wonders if some of the concern isn't fear caused by the publicity over some bad DePuy cases.
But to be safe, he's stopped putting MoM devices in his patients and thinks it's reasonable for the FDA to put a temporary hold on their use until safety issues can be clarified. "I don't know that they're bad. But I don't know for certain that they're safe, and I don't want to take that chance with my patients," he says.