Prior to 1976, the FDA had no control over medical devices whatsoever. During that time a limited number of metal-on-metal hip implants were marketed in the United States, despite documented concerns regarding toxicity of metal ions in the human body. In 1976 medical devices were added to the Food, Drug and Cosmetic Act, placing metal hip implants under FDA regulation. At this time metal-on-metal hip implants were categorized under a Class III or “high risk,” category. Nonetheless, the FDA made the determination to allow regulation of hip implant devices through the 510(k) fast track approval process. Metal-on-metal hip implants were not widely used during the next twenty years, however by the late 1980’s, second-generation metal hip implant designs had been introduced.
In 1990, the World Health Organization International Agency for the Research on Cancer listed trivalent chromium ions as potential carcinogens. By 1998, the FDA had approved a larger head size for metal-on-metal hip implant devices and, once again, these larger heads sailed through the 510(k) process with very little clinical testing. In 2004, many metal hip implant manufacturers modified their design by shortening the taper which connects the components to one another. This particular modification was later found to be responsible for higher failure rates, increased amounts of wear and excess levels of metal ion debris.
From this point on, many manufacturers jumped wholeheartedly on the metal-on-metal hip implant bandwagon, touting these new devices as lasting much longer than the ceramic, polyethylene or metal-on-plastic devices most commonly used. Of course patients were left to assume that the metal hip implants must be safe or their surgeons would not be recommending them. Most people also assumed that safety testing for the metal-on-metal hip implants had taken place, including clinical trials. In March, 2011, the British Orthopedic Association discussed concerns regarding the larger diameter all-metal hip implants, concluding such implants should be carefully considered by the surgeon prior to implantation and even avoided when possible.
Two months later, the FDA ordered twenty-one manufacturers of metal-on-metal hip implant devices to conduct post-market studies of their particular device, addressing metal ion debris specifically. Findings presented at the MHRA (The Medicines and Healthcare Products Regulatory Agency) in February, 2012 stressed that those with large diameter head metal implants must undergo annual monitoring for the life of the implant. Recommended tests included blood tests to determine levels of cobalt and chromium, MRI’s, ultrasound and other tests as recommended by the patient’s physician.
An article published in the British Medical Journal detailed the potential dangers of all-metal hip implants, and by March 1, 2012, the British Hip Society had recommended a ban on metal-on-metal hip implants. A study claiming that all-metal hip implants fail much more often than ceramic, polyethylene and metal-on-plastic implants was published in the Lancet on March 13, 2012. The article placed the overall revision rates for metal-on-metal hip implants at 6% within five years as compared to 1.7-2.3% for implants made from other materials. The problems associated with specific metal hip implants follows.