to the lymph nodes, spleen, liver, and kidneys before being excreted in urine. 6 Metal ions and genotoxicity Multiple studies and research organisations have warned about the carcinogenic potential of metal-on-metal hips. 7 That cobalt and chromium ions lead to genotoxic changes both in laboratory settings and in animals was described in scientific journals over 30 years ago. 8 Cobalt too was shown to be linked to cardiomyopathy in 1966. 9 However, the link to cancer is not proved. From left to right: Large diameter metal-on-metal hip implant highlighting wear pattern caused by toggling on models with short tapers; Chris Bulstrode, orthopaedic surgeon, Oxford University, tried to warn the Department of Health about overzealous innovation; Cobalt-chromium can release metal ions that can seep into local tissue causing reactions which destroy muscle and bone; Nick Freemantle, professor of clinical epidemiology: "We shouldn't be in this position where there's so much uncertainty" In 1990, the World Health Organization International Agency for the Research on Cancer released a monograph listing hexavalent chromium as a proved carcinogen; trivalent chromium a potential carcinogen; and cobalt ions a probable carcinogen. 10 Only recently -- after the early failure of thousands of implants -- have tests from the London Implant Retrieval Centre, a centre that tests prostheses, confirmed that trivalent chromium is the ion being released. 11 The manufacturers were aware of the potential for genotoxicity. The BMJ and Newsnight have seen a DePuy internal memo from July 2005, that says: "In addition to inducing potential changes