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Metal-on-metal hip devices have risen to the top of the stack of causes for concern, eclipsing other devices, including leaking breast implants, according to the British Medical Journal (BMJ) and the British Broadcasting Corporation (BBC). A major reason is the metal hip devices can cause other difficulties, according to a February 28 article by Makiko Kitamura in Bloomberg News, due to exposure of patients “to high levels of toxic cobalt and chromium ions that can seep into tissues and destroy muscle and bone, leaving some patients with long-term disability.” Kitamura points out that studies have also shown, that “metal ions can seep into the bloodstream, spreading to the lymph nodes, spleen, liver and kidneys.” The BMJ and BBC examined hip devices made by Johnson & Johnson of New Brunswick, New Jersey; Warsaw, Indiana-based Zimmer Holdings Inc.(ZMH); and Smith & Nephew Plc (SN/) of London.

The rising trend for patients needing repeated procedures of hip device implantation has caused physicians and patients around the world some alarm. In August 2010, Johnson & Johnson recalled some of their hip implant devices – the ASR metal on metal model – as some patients had to have the implantation repeated when the hip joint caused painful symptoms, including metallosis resulting from toxic levels of chromium and cobalt in their bodies.

Over the years, manufacturers of hip replacement devices have increasingly used plastic in the joint design and manufacture as opposed to metal, in order to “improve movement and decrease dislocation.” According to Kitamura, while the European Union and United States both require manufacturers to prove their new products are safe for use in humans, only the U.S. Food and Drug Administration (FDA) mandates they also show devices are effective. It is believed that the EU’s pre-market studies are not as rigorous as the pre-market studies in the U.S. due to the differing approval procedures. The EU has a “decentralized network of about 70 ‘notified bodies’ which ensure that a device can be marketed—and most of those bodies are not government agencies but are for-profit companies. In the U.S., however, a manufacturer may avoid the more rigorous FDA approval process if its device is substantially similar to a device already having gone through the formal process. The recalled Johnson & Johnson (DePuy) ASR hip implant did not go through the full FDA process.

No matter the process, once approved, the device may still have defects. The trend in recalls (see, e.g., the DePuy ASR hip implant), and repeated implantation of devices, bears this out. Further, the checks and balances implemented by regulatory agencies are only as good as their design and enforcement quality. Ultimately, however, the responsibility for safety rests with the manufacturer.

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