Experts are calling for controversial metal-on-metal hip implants to be banned after they found “unequivocal evidence” of high failure rates.
It comes two weeks after the Medicines and Healthcare products Regulatory Agency (MHRA) issued new guidance on the implants, saying almost 50,000 patients in the UK will need annual blood or MRI checks.
Tiny metal ions made up of cobalt and chromium are thought to break off from the implants and leak into the blood, with fears this causes muscle and bone damage as well as neurological issues.
The MHRA says there is a “small risk” the implants can cause complications in patients.
The research, published in the Lancet medical journal and based on the National Joint Registry of England and Wales, found metal-on-metal implants failed much more quickly than other types of implant, with a five-year revision rate of 6.2%.
This compared with 2.3% for ceramic-on-ceramic implants and 1.7% for metal-on-plastic types.
Failure was related to the head size of the implant, with larger heads failing more quickly.
This was equivalent to a 2% increase in the risk of failure for each 1mm increase in head size.
By contrast, ceramic-on-ceramic types of implants performed better with larger head sizes.
The analysis included more than 31,000 metal-on-metal implants. It looked at patients given implants between 2003 and 2011 and tracked for up to seven years after surgery.
The results showed stark differences between the implants depending on type and head size, and confirm previous findings on failure rates.
In women, failure rates for metal-on-metal were up to four times higher than for other types, and were also higher compared with men even with the same head size.
At seven years after surgery, some revision rates were as high as 10%, such as for 55-year-old women with a 46mm head implant. For women with a 36mm head, the revision rate was 8.4%.
At five years after surgery, revision rates were 6.1% for women with a 46mm diameter metal-on-metal implant, compared with just 1.6% for those with a 28mm metal-on-plastic implant.
In men aged 60 with metal-on-metal implants, revision rates were 3.2% for a 28mm head, jumping to 5.1% for a larger 52mm head.
The experts concluded: “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.”
The authors said they agreed with current MHRA advice but surgeons should seek to use other implants.
Alison Smith, a statistician in orthopaedic surgery at the University of Bristol, added: “We think there are better alternatives so we don’t see a reason to use stemmed metal-on-metal implants any longer.”
Around 65,000 people in the UK have received metal-on-metal hip implants since 2003, of which 49,000 are affected by the MHRA’s guidance because the joint head is 36mm or greater.
Hip replacements are mostly used for patients with osteoarthritis, where there is substantial wear and tear on the hip joint.
The use of metal-on-metal implants has declined in England and Wales, but data suggests they are still used extensively in the US.