Investigation raises new concerns over toxic metals in failing hip implants: new guidance issued
Published on 28 February 2012
An investigation carried out jointly by the British Medical Journal (BMJ)/ BBC Newsnight has raised further concerns about controversial metal-on-metal (MoM) hip implants.
Hundreds of thousands of people around the world may have been exposed to high levels of toxic metals from failing implants, according to the researchers, whose findings will be broadcast on BBC Newsnight tonight (Tuesday February 28th).
They found that cobalt and chromium ions can seep into patients' tissues, damaging muscle and bone near the implant and in some cases causing long-term problems.
These metal ions can also enter the bloodstream and travel to the lymph nodes, spleen, liver and kidneys, and may also cause genetic changes.
Researchers say that some of these problems were apparent as far back as 1975, but that manufacturers and regulators failed to raise the alarm.
The problem has been intensified by the fact that metal-on-metal hip implants did not have to pass any clinical trials before being used in patients.
In addition, manufacturers have changed the design of metal hip implants over time, without conducting new trials to assess their safety and effectiveness.
It is thought that these design changes - which included making the 'head' larger and part of the 'stem' shorter - may be responsible for the release of high levels of metal ions into the body.
In a BMJ article accompanying the BBC's Newsnight programme, Dr Carl Heneghan and colleagues at Oxford University's Centre for Evidence-Based Medicine said: "No pre-market system can ensure all devices are safe, but they can certainly make it more likely.
"Creating an independent system for post-marketing analysis for implantable medical devices that is robust and increasing international coordination around device alerts and withdrawals should go some way to sorting out the current mess."
Nick Freemantle, professor of clinical epidemiology and biostatistics at University College London, said: "We shouldn't be in this position where we don't know and there's so much uncertainty.
"The stability of a compound should have been ascertained before it was used widely in people. As yet, we don't know the consequences of this."
Dr Fiona Godlee, the BMJ's editor in chief, noted that hip replacements have been "one of the great successes of modern medicine".
"But a combination of inadequate regulation and untrammelled commercialism has caused actual and potential harm for large numbers of patients around the world," she observed.
"They should have known about the risks, as the manufacturers and regulators did, but they were not told."
The Medicines and Healthcare Products regulatory Agency (MHRA) issued new guidance for people with MoM implants, saying there was a "small risk" the implants could cause complications in patients.
Some 49,000 people in the UK whose hip replacements have a head diameter of 36 millimetres or more will now need annual blood tests to check their blood ion levels.
They will need these tests every year for the lifetime of their implant.
Guidance published in 2010 said patients with large-head MoM implants should have annual checks for the first five years of the implant, although it is unclear how many people actually received the checks.
A spokesman for Arthritis Research UK said: "We are supporting the MHRA's investigation into MoM implants, and are working alongside the National Joint Registry, the British Hip Society and the British Orthopaedic association to review relevant safety information as it arises.
"We have been funding research into the possible biological effects of contamination of the body through absorption of metals from the implant, but the precise clinical implications are not certain and further research is needed."
The charity is setting up an expert working group to investigate the possible long-term complications of metal-on-metal hip replacements and to advise on research priorities.
Read our Q&A on metal-on-metal hip replacement.
Read some of the recent stories on hip resurfacing and hip replacement below:
Metal on metal hip replacement and resurfacing
'Poster lady' for hip resurfacing implant sues manufacturer
Women face greatest risk from problematic metal-on-metal hip devices
Meet the expert: Professor Anne Neville talks about her work
Researcher to investigate hip replacement costs in bid to save the NHS money