Hundreds of thousands of people have been fitted with replacement hips whose flawed design may be exposing them to toxic metal, according to a probe by the BBC and the British Medical Journal (BMJ) unveiled Tuesday.
It pointed the finger at DePuy Orthopaedics, a subsidiary of the US medical conglomerate Johnson & Johnson, saying that the firm continued to sell the hips even after it knew of the risk.
The risk of leakage from cobalt-chrome implants has been known since 1975, when doctors discovered that local tissue reacts to ions, or charged atoms, from these metals, the investigators said.
"The ions can also leach into the bloodstream spreading to the lymph nodes, spleen, liver and kidneys before being excreted in urine," the BMJ said.
Lab research has also linked cobalt to a heart condition called cardiomyopathy and identified chromium ions as a probable carcinogen, it said.
The BMJ and the BBC news programme Newsnight said they had seen a DePuy internal memo from 2005.
"In addition to inducing potential changes in immune function, there has been concern for some time that wear debris may be carcinogenic," the memo reportedly said.
Despite this, "DePuy's marketing of metal-on-metal hips continued unabated, with promotional material failing to reflect internal company concerns," the BMJ-BBC probe charged.
In 2010, DePuy withdrew its ASR hip prosthesis and promoted another design called Pinnacle as "an alternative for the majority of patients."
But Pinnacle too had metal-on-metal problems and the following year, British researchers warned the national health safety watchdog of failures with this model, the report said.
There was no immediate response from DePuy to the allegations.
The investigation heaped blame on US and European health regulators for failing to respond to concerns or even requiring monitoring of patients who had received hips capable of producing toxic debris.
"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," said BMJ investigations editor Deborah Cohen.
"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."
The controversy coincides with a scandal over faulty breast implants.
More than 400,000 women around the world are thought to have received implants made by a French firm, PIP, which shut in 2010 after it was found to have used substandard, industrial-grade silicone gel.