Two large studies being presentedin 2010 at the annual meeting of the American Academy of Orthopaedic Surgeons (AAOS), in New Orleans, are offering new information on the best hip replacement options for younger patients with worn-out hips.

Total hip replacements have been performed on older patients for long enough now that doctors say the results are usually predictable, but less is known about the best ways to replace hip joints in patients who are younger, a group that is increasingly driving demand for these procedures. 

In fact, one 2009 study projected that people younger than age 65 could account for more than half of all hip replacement patients as early as next year.

Because joint implant components wear out over time, younger patients often require what’s called a revision hip replacement surgery to replace the implant, or prosthesis.

Those second surgeries are complicated and often aren’t as successful because total hip replacement, the standard method of joint replacement, requires removing a significant amount of bone. Plus, the bone that remains has often deteriorated over time, making it hard to properly fit and anchor the replacement implant.

So a more conservative method of hip replacement called hip resurfacing, which was designed to preserve bone, has been gaining in popularity among surgeons who treat young, active patients. 

Hip resurfacing is a bit like putting a crown on a tooth instead of pulling the tooth altogether. Instead of removing the top of the femur, including the ball that fits in the hip socket, and replacing it with a ball-and-stem implant, surgeons who do hip resurfacing reshape the ball of the joint and cover it with a metal prosthesis. 

But now evidence is emerging that hip resurfacing isn’t always the best choice for younger patients.

Researchers from the University of Adelaide, in Australia, have released findings from their study of the outcomes from 12,093 hip resurfacing procedures reported to their country’s national registry.

They found that hip resurfacing has a significantly higher rate of revision than conventional total hip replacement – 5.3 percent compared to 4 percent eight years after the procedures. They say most hip resurfacing procedures need to be revised because of fractures and loosening.

Other factors that appear to influence the longevity of these procedures are the age and sex of the patient and what sort of prosthesis was used.

The lowest rate of revision was in men with osteoarthritis (OA) younger than age 55 who needed a femoral resurfacing component of 50 mm or greater. Their rate of revision – 3 percent, was the same as in people who had a total hip replacement.

“I think what this does is reinforce that resurfacing does best in younger male patients with osteoarthritis,” says Craig Della Valle, MD, an associate professor of orthopaedic surgery at Rush University Medical Center in Chicago who specializes in joint replacement. “In general, those are the same patients who do worse with a conventional total hip replacement,” he continues. “Those are the patients that run into the most problems, so it’s kind of nice that is the demographic that does the best with resurfacing.”

The study also shows that things get a bit more complicated when it comes to women.

Researchers say while at first it appears that females are at a higher risk for early failure and fracture from resurfacing, a closer look at the data shows it’s not gender, but a person’s size that actually determines that. It just so happens that smaller patients are also usually women.

“It’s size of the patient and quality of the bone, and there are technical factors at place as well,” says Dr. Della Valle. 

“If you held in your hand a 50 mm head [the part that replaces the ball of the hip joint] and a 44 or 42 head, the 50 mm head doesn’t sound that much bigger but it’s almost twice the size when you hold it in your hand because of the volume," he adds.

Edwin Su, MD, an orthopaedic surgeon at the Hospital for Special Surgery in New York City agrees. “The best candidates are men under the age of 55 as a blanket statement. But there are some women who are large boned and have good bone quality that it also seems to work well for.