Once touted as a breakthrough in hip implants and widely available in New York, a recent study in the British Medical Journal (BMJ) found no advantage to metal-on-metal implants over more traditional types of hip implants that include other materials. Instead, the Federal Drug Administration (FDA)-sponsored study indicated that patients who had the metal-on-metal implants were more likely to require a second surgery on the injured hip.
The new report comes after one popular all metal hip replacement system - the ASR hip implant produced by DePuy Orthopaedic - was recalled in August 2010 due to an unexpectedly high rate of failure.
The BMJ study is a composite review that included 18 smaller studies of hip implant patients. In total, over 3,000 patients were involved and about 830,000 surgeries were documented from national registries. Those registries included England and Wales, New Zealand and Australia. The United States does not maintain a registry for hip implant surgeries.
Dangers of Metal-on-Metal Implants
Upon their introduction, the metal-on-metal hip implants were thought to be more resilient than previous systems. Older versions often use a combination of metal and plastic or polyethylene. More recently, concerns arose over possible side effects of the all metal implants, including joint dislocation, swelling, premature failure and even severe tissue damage from toxic chromium and cobalt, which can be released as the parts begin to wear over time.
The study did not identify any statistical advantage to the metal-on-metal implants in their performance of daily functions. It further found that the all-metal hip implants required replacement at twice the rate of their counterparts.
While researchers cautioned that the review was preliminary, they noted that it is unlikely a larger study would contradict the outcome that the metal-on-metal implants failed at a higher rate.
What Should Patients Do?
Following the recall of the ASR hip implant, the FDA requested that manufacturers of metal-on-metal hip implants conduct follow-up studies on patients using their devices.
Some doctors are not waiting for confirmation of a problem, as one respected orthopedic surgeon at the Hospital for Special Surgery in New York has already stopped using the all-metal implants due to the concerns. Until the final results from the manufacturers are collected and analyzed, researchers suggest that patients discuss all options with their doctors before choosing a particular hip implant.