Metal-on-metal hip implants are more likely to fail than devices made from other materials and should be banned, U.K. researchers said after reviewing the world’s largest database on hip replacements.
More than 500,000 patients in the U.S. and 40,000 in the U.K. have metal-on-metal hips and are at higher risk of device failure, according to the analysis, which was published today in The Lancet. Failure rates were as much as four times higher in women, who are likelier to have implants containing a larger prosthetic femoral head.
The use of larger metal implants became popular because it was thought that they reduced the likelihood of dislocation and were highly resistant to wear, researchers led by Ashley Blom from the University of Bristol in the U.K. wrote in the study. Manufacturers of the devices include Johnson & Johnson, Zimmer Holdings Inc. and Smith & Nephew Plc.
Metal-on-metal implants failed much more quickly than those with other surfaces. Overall, 6.2 percent of patients need a second operation in five years. The larger the hip, the earlier they failed -- each 1-millimeter increase in femoral head diameter corresponded to a 2 percent increase in the risk of failure. Larger ceramic-on-ceramic implants fared better in the analysis, the researchers said.
“Metal-on-metal stemmed articulations give poor implant survival compared with other options and should not be implanted,” Blom and his colleagues wrote. “All patients with these bearings should be carefully monitored, particularly young women implanted with large diameter heads.”
Researchers analyzed data from the National Joint Registry of England and Wales, which includes information on more than 400,000 hip replacements implanted between 2003 and 2011, and tracked for up to 7 years after surgery. Of those, 31,171 were metal-on-metal. The registry funded the research.
The study follows findings reported last month that hundreds of thousands of people worldwide may have been exposed to high levels of toxic cobalt and chromium ions that can seep into tissues and destroy muscle and bone, leaving some patients with long-term disability, according to an investigation by the British Medical Journal and the British Broadcasting Corp.
Many medical devices didn’t undergo clinical testing like that required of drugs before they were used in patients, the BMJ and BBC said at the time. Manufacturers have replaced plastic with metal materials over the last decade to improve movement and decrease dislocation without conducting safety studies, they said.
“Policy makers need to appreciate that registry data alone are not a substitute for good pre-marketing studies, which should include testing of implants,” Art Sedrakyan, an associate professor of public health at the Weill Cornell Medical College at Cornell University in New York, wrote in an accompanying commentary. “When failures take a long time to develop, many faulty products can enter the market.”
DePuy Orthopaedics Inc., a unit of Johnson & Johnson, pays royalties related to a cemented total hip prosthesis to one of the researchers, Martyn Porter. The other four authors declared no conflict of interest.