‘All-metal’ hips may fail more often study finds as experts call for a ban

By Dr. Ananya Mandal, MDMar 14 2012

New research has shown that ‘metal-on-metal’ also called ‘all-metal’ artificial hips fail more often than other types and researchers have called for a ban of this type this Tuesday.

The analysis in The Lancet medical journal came two weeks after Britain's medical regulator said nearly 50,000 Britons with metal-on-metal hips needed annual check-ups to monitor for problems, including exposure to toxic metals.

This controversy again brings up the debate on the regulation of medical devices in the wake of a scandal over French-made breast implants and faulty leads on some heart defibrillators.

Metal-on-metal hips were developed to be more durable than traditional implants, which combine a ceramic or metal ball with a plastic socket. But recent experience suggests they may actually do worse, prompting the recall of one device made by Johnson & Johnson that critics argue should never have been allowed on the market.

The team from the University of Bristol analyzed data from the National Joint Registry of England and Wales covering more than 400,000 hips replacements, including 31,171 all-metal ones, that were undertaken between 2003 and 2011. The study was carried out by researchers from the Universities of Bristol and Exeter, and the Centre for Hip Surgery at the Wrightington Hospital in Lancashire. It was performed on behalf of the National Joint Registry of England and Wales, which also funded the research.

Results from the most comprehensive study to date now show that there is a 6.2 percent chance patients with all-metal hips will need a replacement within five years - some three times greater than the revision rate seen with older implants. The rate was particularly high with larger-head implants and those used in women, in whom failure rates were up to four times higher, the researchers said.

The results, they said, were unequivocal, “Metal-on-metal stemmed articulations give poor implant survival compared with other options and should not be implanted.” Their analysis did not cover resurfacing systems, which avoid the use of a stem sticking into the bone, such as Smith & Nephew's Birmingham Hip Resurfacing joints.

Art Sedrakyan of Cornell University said the problem highlighted weaknesses in the regulatory systems on both sides of the Atlantic due to “outdated and low-threshold regulatory pathways”. In a strongly worded Lancet commentary accompanying the latest research, he called for better studies before implants reach the market. “We are left with more than 500,000 patients with metal-on-metal prostheses in the USA and more than 40,000 in the UK who are at elevated risk of device failure, which will inevitably result in the burden of further surgical treatment as well as billions of dollars in costs to taxpayers,” he said.

Ashley Blom of the University of Bristol said that total hip replacement surgery remained a very successful operation for the vast majority of people but regulators should learn lessons as they seek to balance safety against innovation. “In this case, with the benefit of hindsight, I think that tighter regulation may have prevented this,” he told Reuters.

Under the new guidelines from Britain's Medicines and Healthcare Products Regulatory Agency (MHRA), doctors are being advised to consider removing and replacing implants if patients have abnormal MRI scans or if metal ion levels in the blood reach worrying levels. With the exception of J&J's DePuy ASR system, which was pulled from the market in 2010, the MHRA decided in its recent ruling against a ban on use, arguing that stemmed metal-on-metal implants could still be good news for some patients. Other companies that make metal-on-metal hip implants include Zimmer, Stryker, Corin and Biomet.