In a disturbing development, experts in the U.K., including the British Hip Society, have asserted that metal-on-metal hip implants devices with large bearings, over 36mm, should no longer be used because of their high failure rate. Professor Joe Dias, President of the British Orthopaedic Association, told the Daily Telegraph that about 5.5% of all large metal-on-metal implants required replacement within five years versus 2% for older generation plastic devices.
“It is clear that as a class these large metal-on-metal implants, which were introduced to make the implant last longer in younger patients, are not fulfilling that aspiration. Because they are not fulfilling that aspiration, in that at the moment they are worse than metal on plastic, it does not make sense that surgeons continue to use them,” Dias said.
A statement issued by the British Hip Society at its meeting in Manchester last week agreed:
“The British Hip Society advises that stemmed, large diameter metal-on-metal primary total hip replacements using bearings of 36 mm or above should no longer be performed until more evidence is available, except in properly conducted and ethically approved research studies.”
This is just the latest in a string of bad news relating to metal-on-metal hip implants. Just last week we reported that the British Medical Journal (BMJ) had raised issues over how U.S. and international regulators were responding to growing evidence of the health risks posed by all-metal hip implants. The investigative report, a collaboration the BMJ and BBC Newsnight, revealed that hundreds of thousands of people worldwide may have been exposed to dangerously high levels of toxic metals from failing metal-on-metal hip implants, thanks to an inadequate response by medical device regulators, including the U.S. Food & Drug Administration (FDA).
We’ve long written on the dangers posed by metal-on-metal hip implants, noting that many experts believe the devices can shed microscopic metal shards into the surrounding tissue, causing local reactions that destroy muscle and bone, and lead to long-term disability. Studies reveal that metal ions can leach into the bloodstream, spreading and poisoning organs in the body. Recently, preliminary findings from a study conducted by researchers at the University of Bristol in the U.K. indicated that patients fitted with all-metal hip implants may be at risk of experiencing genetic changes to the cells of the bladder, a possible precursor to cancer, and possibly bladder cancer itself.
Just last month, the U.K.’s Medicines and Healthcare products Regulatory Agency (MHRA) announced that blood tests should be conducted yearly to check cobalt and chromium blood levels in some all-metal hip implant recipients, those with bearings of 36 mm or above. Those who do exhibit high metal ion levels should be subjected to MRI to check for damage near the implanted joint, the agency said. According to the agency, patients implanted with joints smaller than 36mm and patients who only received a hip resurfacing procedure are not affected. The British Hip Society released a statement during its meeting in Manchester last week agreeing with this advice, according to the Telegraph.
According to the Telegraph, Dias and Dr. Susanne Ludgate, Clinical Director of the MHRA, both stressed that the implant type has not been linked to increased cancer risks. However, DePuy Orthopaedics—maker of metal-on-metal hip implants such as its ASR Hip Resurfacing System and the ASR Acetabular Hip Implant System, which were recalled in 2010 because of an unusually high premature failure rate—said in a 2005 memo regarding the ASR hip implant devices that: “In addition to inducing potential changes in immune function, there has been concern for some time that wear debris may be carcinogenic. The mechanism is not known and only 24 local malignancies have been reported in patients with joint replacements. Also worrying is the possibility of distant effects. One study suggested a threefold risk of lymphoma and leukemia 10 years after joint replacement,” according to the BMJ report.
Years prior, said BMJ, evidence was mounting about high metal concentrations in patients fitted with those devices. According to the article, DePuy itself appeared to have been aware of one significant problem associated with the ASR hip implants known as genotoxicity, a condition in which the metal ions shed from the devices altered the DNA of the cells, thereby causing cancer or mutation. Despite this, DePuy aggressively marketed the devices.