An alternative operation to hip replacements has a high failure rate, a British study suggests.

Hip resurfacing is similar to total hip replacements except the rounded top section of the thigh bone, called the femoral head, is replaced with a metal cap instead of removing it completely.

si-implant-hip-220-cp-36363

Regulators worldwide are looking at the failure rates of various types of hip implants. (Charles Rex Arbogast/Associated Press)

Hip resurfacing uses metal-on-metal bearings and is often used as an alternative to hip replacements in younger, active patients.

Authorities in Canada, the U.S. and the UK have issued warnings about full metal-on-metal hip implants, saying they may be more likely to fail and can cause tissue damage around the joint compared with the traditional metal-and-plastic type of implants.

Researchers at Bristol University in the UK compared how many total hip replacements and resurfacing implants failed over seven years, based on data from a national registry of more than 400,000 first hip replacement procedures.

About seven per cent of the operations were resurfacings.

Using smaller metal caps was associated with higher failure rates, lead researcher Dr. Ashley Blom, an orthopedic surgeon at the University of Bristol and his co-authors found.

"Resurfacing failure rates in women were unacceptably high. In view of these findings, we recommend that resurfacing procedures are not undertaken in women," Blom said in a release.

Surgery trade-offs

In women, 8.5 per cent of resurfacings had been revised by five years compared with 3.6 per cent in men, the researchers said. More than two-thirds of the procedures were done in men.

Women tended to fare worse than men even when the same  size of cap was used, Blom's team reported.

The patients weren't randomly assigned in the study. The investigators can't draw any cause-and-effect relationships. 

The study's authors said that load on the hip from activity and body mass index might make a difference to implant failure rates, adding it's hard to measure.

In a journal commentary accompanying the study in this week's BMJ, Dr. Art Sedrakyan of Weill Cornell Medical College in New York suggested that regulators and surgeons use specific and evidence-based information on the risks and benefits of hip implants when communicating with patients.

"There might be a trade-off between higher occurrence of revision and better functional outcomes, which could be important for patients who are doing more physically demanding work or participate in sports," wrote Sedrakyan, who studies medical device epidemiology.

The National Joint Registry for England and Wales funded the research.