Hip-replacement patients fitted with all-metal large-diameter modular implants, such as DePuy’s ASR hip devices, are more than three times likely to need to need their devices replace prematurely, according to a new report by the Canadian Institute for Health information (CIHI).
While the Canadian report doesn’t shed new light on the risks many metal-on-metal hip devices pose, it echoes the findings of many previous studies and reports that have found certain types of all-metal hip implants are, by design, prone to fail early and injure the patient.
The CIHI based its conclusions on voluntary data for 56,942 hip-replacement surgeries performed in all but one of the Canadian provinces from 2003 to 2011. Data from Quebec was not included.
According to CBC News, about 40,000 Canadians undergo hip implant surgery every year. The majority of those – 73 percent – receive conventional hip implants made of both metal and polyethylene plastic. Ranking second are metal-on-metal hip implants, which the study found accounted for 9 percent of the hip replacements in Canada, followed by ceramic-on-ceramic (8 percent), and ceramic-on-plastic (5 percent).
Researchers found that “Patients with a specific type of metal-on-metal hip replacement (large-diameter modular implants) had a 5.9 per cent chance of needing a second implant within five years compared with 2.7 per cent chance among those with the most common type of metal-on-plastic implant (metal-on-cross-linked polyethylene),” CBC News reported.
Problems with metal hips stem from the erosion of metal fragments into the tissue and blood, where they become ionized and potentially cause bone and tissue decay at the implant site (a condition known as metalosis), hip device dislocation, bone fracture, severe pain, inflammation, and a spectrum of illnesses caused by metal poisoning — excessively high levels of cobalt and chromium metals in the blood.
DePuy recalled its metal ASR hip devices in August 2010 after they had been implanted in about 93,000 patients worldwide, including some 37,000 Americans. The recall came amid evidence from a U.K. joint registry that the ASR hips failed at a rate of 12 to 13 percent within five years. Subsequent research has demonstrated that the ASR failure rate could be significantly higher.
The frustrating irony with metal hips like DePuy’s ASR is that they were designed to be more durable and longer lasting than conventional hip implants with plastic and ceramic parts, which usually last up to 15 years. The theoretical longevity of metal hips made them a perfect fit for younger patients, who need the implants to last more than 10-15 years, and patients who live a physically demanding lifestyle.
Unfortunately, high metal-hip failure rates mean earlier-than-expected revision surgeries for many, and recovery time becomes longer with each replacement, especially when the bone and tissue around the implant site has been damaged by metal erosion.