Following the breast enhancement scandal last month, the latest storm in the medical world is the concern that metal-on-metal hip replacements are seeming to exhibit a high failure rate.
In a follow-up to an announcement from The Medicines and Healthcare products Regulatory Agency (MHRA) nearly two weeks ago, stating that: patients who have received stemmed metal-on-metal (MOM) hip replacements will need an annual check-up, The Lancet has published further evidence, collected from the largest database on hip replacements in the world.
Whilst stemmed MOM hip implants are not as popular as they were in the UK, data suggests that they still represent more than a third of replacements done in the US, as of latests figures from 2009. The model became popular because there was a belief that the larger head would be less likely to dislocate and be more resistant to wear and tear.
On the contrary, however, the research from Ashley Blom of the University of Bristol, UK, shows stemmed MOM failing much more quickly than other types of bearing surface, with a 5-year revision rate of 6.2%. Failure was related to head size, with larger heads failing earlier, corresponding to a 2% increase in the risk of failure for each 1mm increase in head size. By contrast, ceramic-on-ceramic implants did better with larger head sizes.
The Lancet article confirms that stemmed MOM implants are showing higher rates of failure than other types, including those with larger head sizes and those implanted in women. The authors are calling for a ban on the use of stemmed MOM hip implants.
Blom analyzed data from the National Joint Registry of England and Wales, including more than 400,000 hip replacements (of which 31,171 were MOM). Procedures were carried out between 2003 and 2011 and were tracked for up to 7 years after the surgery. Blom and colleagues looked at failure rates for stemmed MOM implants, based on different head sizes, and then compared them with comparable implants made from ceramic and polythene.
Women had the worse failure rates for stemmed MOM implants, coming in up to four-times higher than those of other bearing surfaces. Rate were also higher in men even, with the same head size. The authors conclude:
“Metal-on-metal stemmed articulations give poor implant survival compared with other options and should not be implanted. All patients with these bearings should be carefully monitored, particularly young women implanted with large diameter heads.”
Art Sedrakyan from Weill Cornell Medical College, Cornell University, New York, warns of the current situation in the USA:
“The National Institutes of Health is interested in new discoveries and, until recently, not in infrastructure for comparative safety and effectiveness…There is also substantial pressure from Congress not to stifle innovation and to undertake faster reviews…[These practices] fail to recognise that only a large national, or even worldwide, registry can address the needs when more than 10 000 products are on the market for the same purpose.”
Furthermore, he adds that:
“Policy makers need to appreciate that registry data alone are not a substitute for good premarketing studies, which should include testing of implants. When failures take a long time to develop, many faulty products can enter the market. In the case of the ASR and metal-on-metal implants it took 4 to 5 years before evidence was accumulated and reported. We are left with more than 500 000 patients with metal-on-metal prostheses in 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.”
Written Rupert Shepherd