How safe are metal-on-metal hip implants?

Hundreds of thousands of patients around the world may have been exposed to toxic substances after being implanted with poorly regulated and potentially dangerous hip devices, a BMJ/ BBC Newsnight investigation reveals this week. Despite the fact that these risks have been known and well documented for decades, patients have been kept in the dark about their participation in what has effectively been a large uncontrolled experiment.

This isn’t the unlucky failure to spot the misdemeanours of one rogue company or the occasional unforeseen breakdown of a small number of devices. It is the inability to prevent a whole class of failing hip implant from being used in hundreds of thousands of people globally—a class of implant that the usually reticent National Joint Registry of England and Wales described recently as a “cause for concern.”1 2 The implants concerned are “metal on metal”—the head at the top and the lining of the cup it fits into are made of cobalt-chromium alloy rather than ceramic or polyethylene—and there are models for both total hip replacement and hip resurfacing.

From their arrival on the orthopaedic scene in 1997, they were marketed as the latest advance in hip replacement and were targeted at young active patients who needed a hip that would last a whole lifetime. And while there is evidence that hip resurfacing works well in young active men,3 the failure rates of resurfacing in women and of metal-on-metal total hip replacements in both sexes are higher than they should be. Average failure rates at seven years are 11.8% for resurfacing and 13.6% for metal-on-metal total hip …