Hip resurfacing – an alternative to total hip replacement surgery – has unusually high failure rates, according to a new study published online in The Lancet. And for that reason the study authors recommend the procedure should be used only in very carefully selected male patients, and rarely in women.

Hip resurfacing is similar to total hip replacement, or THR, except the top portion of the thighbone, or femur, is left in place and capped with a metal, dome-shaped covering. The result is a larger hip ball – called femoral head – that more closely resembles a normal joint. That capped ball then fits into a metal cup that serves as the hip socket.

Using data from the National Joint Registry for England and Wales, the observational study looked at more than 400,000 patients who underwent hip surgery between 2003 and 2011. Of these, 31,932 had resurfacings.  

Theoretically, hip resurfacing should reduce the risk of dislocation, a leading cause of joint failure (along with fractures and loosening) since the femoral head is larger than in traditional total hip replacements.

But University of Bristol researchers found the opposite. Hip resurfacing was associated with significantly higher failure rates than total hip replacement, or THR, especially in women. Failure rates were related to femoral head size, with the smallest sizes more prone to early failure.

Predicted five-year revision rates (ie: those expected to need a second surgery to correct an implant failure) ranged from 6.1 percent for women with a 46 mm femoral head to 8.3 percent for those with a 42 mm head. In comparison, women who received a traditional THR with a 28 mm head had a predicted five-year revision rate of between 1.5 and 2.6 percent (depending on the material used).

Men who underwent resurfacing with smaller-diameter heads also experienced more failures – although at about half the rate of women.

Ashley Blom, MD, a study author and professor of orthopaedic surgery at the University of Bristol, says hip anatomy, poor bone quality or the presence of osteoporosis might account for the greater number of failures in women.

Failure rates for hip resurfacing in both sexes were so high researchers recommended against the procedure in women and in men with smaller body frames.

Dr. Blom sees little room for exceptions. "The evidence that hip resurfacing gives better function is not strong," he says. "A recent paper in the BMJ [described] a randomized controlled trial that showed no difference in pain and function between hip resurfacing and [conventional] stemmed hip replacement. However, the evidence that [resurfacing] implant failure is much higher in women is very strong."