Study Sees no Cancer Risk with Metal-on-Metal Hip Implants, but Can't Rule out Possible AssociationApr 9, 2012 | Parker Waichman LLP
A new study involving metal-on-metal hip implants has found no link between the devices and an increased risk of cancer. However, the study, published in the British Medical Journal, followed patients with all-metal hip replacements for less than a decade, and even its authors concede that metal-on-metal hip implant patients will need to be monitored for far longer before any cancer danger can truly be ruled out.
For this latest study, researchers from the U.K.'s from the University of Bristol, University of Exeter and Wrightington Hospital assessed cancer incidence in 40,576 patients who had undergone metal-on-metal hip replacement and 248,995 patients with alternative bearings. Results indicated that the rate of cancer 7 years after surgery was not significantly higher in those receiving metal-on-metal implants when compared with patients with hip implants made from other materials. The study was based on data from the National Joint Registry of England and Wales.
However, the study authors did point out that patients were not followed long enough to completely disregard a cancer threat from metal-on-metal hip implants. "As some cancers have a long latency period it is important that we study the longer term outcomes and continue to investigate the effects of exposure to orthopaedic metals," they wrote. One of the researchers also told Bloomberg News that study failed to account for a number of factors, including the fact that metal-on-metal hips were marketed to younger patients, who tend to have lower rates of cancer.
Joshua Jacobs, MD, first vice president of the American Academy of Orthopaedic Surgeons and professor and chairman of the Department of Orthopaedic surgery at Rush University in Chicago, Illinois agreed, telling MedScape that follow-up was needed "in excess of 1 to 2 decades, to get a handle on the epidemiology of cancer in those with metal-on-metal hip implants."
Jacobs also said the findings of the British study might not be relevant to the U.S., where metal-on-metal hip implants have been used at a far higher rate (14% in the U.K., versus 35% in the U.S.).
Of course, an association with cancer is not the only worry faced by recipients of metal-on-metal hip implants. When their metal components wear, the devices can leach dangerous amounts of chromium and cobalt into surrounding tissue, and even the blood streams of recipients. This can result in a reaction known as metallosis, which can destroy the tissue around the implant, including muscle and bone. According to the authors of the British Medical Journal, metal ions can cause irreversible damage to DNA in cells, and have been found in many organs following hip replacements, including marrow, blood, liver, kidneys and bladder, the authors of the British Medical Journal pointed out.
In March, authors of a study published in The Lancet said all-metal hip implants should no longer be used because of their high failure rates. The month prior, a report in the British Medical Journal raised fears that hundreds of thousands of people around the world may have been exposed to dangerously high levels of toxic metals from failing metal-on-metal hip implants. The British Hip Society has also called on surgeons to stop using all-metal hip implants in total hip replacement procedures.
In March, the U.S. Food & Drug Administration (FDA) announced that its Orthopaedic and Rehabilitation Devices Panel will meet over June 27 and 28 to discuss the risks and benefits of metal-on-metal hip systems, as well as potential patient and practitioner recommendations for their use. Last May, the agency had asked 21 manufacturers of metal-on-metal hip replacement devices to conduct safety studies of their implants.