Wed, 29 Feb 2012 16:03 UTC
The investigation into the implants found that chromium and cobalt ions from this type of artificial hip can seep into the surrounding tissue to destroy muscle and bone and spread to the lymph nodes, spleen, liver and kidneys, potentially causing damage. The researchers were also concerned the ions could affect a person's chromosomes, resulting in genetic changes.
"This is one very large uncontrolled experiment exposing millions of patients to an unknown risk," Michael Carome, deputy director of the patient advocacy organization, Public Citizen's Health Research Group, said in a BMJ written statement. "We will only find out about the safety of these devices after large numbers of people have already been exposed."
The researchers say manufacturers of metal on metal hip implants changed the design of the hips over the past decade to increase movement for the recipient, but those changes may be responsible for the release of high levels of toxins into the body.
The study was published in the Feb. 28 issue of BMJ, and aired Tuesday night on BBC News.
The investigation also uncovered a 2005 internal memo from implant manufacturer DePuy Orthopaedics, a division of Johnson & Johnson, that shows the company knew about the possible toxicity from implants in 2005.
"In addition to inducing potential changes in immune function," the memo said, "there has been concern for some time that wear debris may be carcinogenic...Also worrying is the possibility of distant effects. One study suggested a threefold risk of lymphoma and leukemia 10 years after joint replacement."
Despite the memo, marketing for the metal on metal hips "continued unabated," according to the investigators.
How? According to the investigators, the FDA approved the design change in 2005, saying it did not "raise any new issues of safety and effectiveness." The U.K.'s regulatory agency, the Medicines and Healthcare Products Regulatory Agency (MHRA), appointed a committee in 2006 that concluded that patients should be told about the risks, but no alert was issued to surgeons or patients until 2010.
What do the regulators say now?
"Clinical evidence shows that patients have a small risk of suffering complications from having metal-on-metal hip implants," Dr Susanne Ludgate, Clinical Director of the MHRA, said in a statement to BBC News. "As a precautionary measure, we have today issued updated patient management and monitoring advice to surgeons and doctors" that they should monitor these implants annually for a patient's lifetime.
The updated British recommendation won't affect U.S. patients, according to the FDA. Erica Jefferson, spokesperson for the FDA, told the New York Times that it was unclear that testing patient blood for metal ions would accurately reflect damage, so it would maintain its existing recommendation.
"We continue to recommend that hip replacement patients undergo regular follow-up with their physicians," she said.
According to Medscape, the FDA cleared the newer metal on metal hip replacement design through a grandfathered process because the design was similar to older implants. Then In May 2011, the FDA ordered metal on metal prosthesis manufacturers to conduct research into whether the implants were making people sick, HealthPop reported. Until recently, about one-third of the 250,000 hip-replacement operations done in the U.S. each year used a metal-on-metal joint implant.
The investigators point the finger at the regulators for letting the issue get this far.
"This isn't the unlucky failure to spot the misdemeanours of one rogue company or the occasional unforeseen breakdown of a small number of devices," BMJ investigations editor Deborah Cohen told BBC News. "It is the inability to prevent a whole class of failing hip implant from being used in hundreds of thousands of people globally."
Nick Freemantle, an epidemiologist and statistician at University College London, who worked as an editorial advisor for BMJ, told CBS News, "In my mind we've got ourselves into a mess."
Freemantle says we're now facing a situation where possibly millions of people in the U.S. have potentially risky hip replacements and the health impact of these metals in bloodstreams are unknown. Compounding the issue, many younger people have the devices since they were designed to last longer. He said regulators should not be in this position of uncertainty.
"It's very worrying for somebody who may have had one of these implants but we don't know whether it's extreme risk or not, and we shouldn't be in that position."
Freemantle thinks the FDA has been too complacent and had not done enough to evaluate the potential risks of these implants.
"I don't think we're in a situation where nothing can be done," he said. "There's no way of pretending there's no problem - we have a problem and it needs dealing with."