Stemmed metal-on-metal (MOM) hip replacements were once hailed as a superior option due to orthopedists belief that the devices had a relatively low risk of dislocation and a high resistance to wear. However, a new study in The Lancet suggests that this type of hip replacement may actually have a higher likelihood of failure than the older standard, ceramic replacement hips and polythene versions.
A researcer from the University of Bristol, England, and colleagues analyzed the National Joint Registry of England and Wales which includes information on over 400,000 hip replacements, more than 30,000 of which were MOM. The procedures occurred between 2003 and 2011, and researchers followed the patients for seven years after the initial surgery.
What the researchers discovered runs contrary to previous evidence on the benefits of MOM hip replacements: Stemmed MOM replacements failed significantly more often and more quickly than any other type of replacement, with a failure rate of 6.2 percent within five years; those implants with larger heads failed even more quickly. Even worse were the results found among women, whose MOM replacements were up to four times more likely to fail than other types.
The study authors go so far as to recommend stopping all implantations of stemmed MOM hip replacements, adding, All patients with these bearings should be carefully monitored. A corresponding commentary in The Lancet explains that, with over 500,000 patients in the U.S. who currently have stemmed MOM hip replacements, this is a real matter of concern.
Yet ACSH s Dr. Elizabeth Whelan reminds people who have this type of hip implant that this study should not be cause for panic. Even though the risk is relatively higher than the risk of other kinds of implants," she notes, "the rate of failure is still low. Since 94 percent are likely to last many years, this should not be evidence to have them removed as a preventive measure, especially considering the much higher risk of actually undergoing a surgical procedure to replace the implant.
Although the commentary suggests expanding premarketing studies to include testing implants, ACSH's Dr. Gilbert Ross emphasizes that although such studies would certainly help somewhat in reducing the risks of new medical devices, requiring large, long-term studies to predict device issues such as this one would have a major chilling effect on innovation for similar new devices.