A major study finds high failure rates for this alternative to total hip replacement.By Linda Rath
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."
Resurfacing was originally targeted to active younger adults because of better wear resistance and because the preserved bone may make it easier to perform total hip replacement later on.
But according to Art Sedrakyan, MD, an associate professor at Weill Cornell Medical College in New York and an authority on comparative effectiveness research, hip resurfacing wasn't limited to this relatively small population. "Thousands of people on Medicare received these implants," he says. "Any technology adopted in the world can be adopted in very unexpected ways. That's why it's important to have clear criteria about who is going to benefit."
Dr. Sedrakyan wrote a commentary accompanying the Lancet report but was not involved in the study. In the commentary, he brings up the issue of the metal-on-metal bearings in resurfacing implants.
A growing number of serious complications including bone damage and cardiovascular and neurological problems have been linked to THR with a metal ball and socket (called metal-on-metal, or MoM) due to the microscopic metal particles that are released into the surrounding tissues and bloodstream as the ball and socket components rub together.
The current study did not look at the safety of resurfacing implants, but researchers say they could present the same risks as metal-on-metal THRs.
Dr. Sedrakyan notes – as he has in the past when speaking about the potential hazards of metal on metal hips – that there are no good studies on the long-term effects of chromium and cobalt ions produced when these metal bearings rub together.
"People get resurfacing implants at a relatively young age, and we don't know what happens after 20 or 30 years of metal ion exposure," he says. "If hip resurfacing devices are found to be unsafe, then the implications are grave."
Regulatory agencies in the U.K. advise annual checks and imaging tests for people with metal-on-metal hip systems, but no such guidelines exist in the U.S. In June, a Food and Drug Administration advisory panel took the first step by recommending that patients experiencing symptoms from all-metal hips have annual X-rays and metal ion testing.
Dr. Blom tells resurfacing patients not to worry too much, but suggests similar precautions: "If you have pain, I would advise an annual review by surgeons, have your metal levels checked and a MARS MRI of the hip," he says. A MARS (Metal Artifact Reduction Sequence) MRI cuts down on distortions to the image caused by the metal implant.
As to whether female patients should continue to undergo hip resurfacing, Thomas Vail, MD, chair of the department of orthopaedic surgery at the University of California, San Francisco, agrees with the researchers. "I would concur with the findings of the authors that indications for metal-on-metal implants should be stringently applied,” he says. “Based upon the emerging information, it would seem that the indications for metal-on-metal hip resurfacing in women are increasingly limited to surgeons with technical expertise in resurfacing and female patients with special cases where total hip replacement might be less desirable."