The fallout over metal-on-metal hips distributed in the US and UK continues as a new article in the British Medical Journalalleges that hundreds of thousands of patients have been exposed to toxic substances as a result of being implanted with the devices.

"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," writes the article's author, Deborah Cohen.

Metal shavings from the metal-on-metal hip implants are releasing metallic ions into surrounding tissues, said Cohen, who noted that the World Health Organization has found several of the present substances to be proven or suspected carcinogens.

"[T]he regulators in Europe and the US failed to identify the design changes and their consequences for patient safety," writes Cohen, referring to the devices' approval via the 510(k) pathway, which looks at whether or not a device is substantially equivalent to a predicate device. Previous iterations of the hips did not use metal in the re-surfaced hip sockets, but the devices were cleared via the 510(k) pathway anyways.

"It's intrinsically tricky to know when you have a different device," says Professor Nick Freemantle of University College London.

"Regulators find this very difficult to spot. But it can't be the decision of the manufacturer when they need more scrutiny,"

Read more:

BMJ - How safe are metal-on-metal hip implants?