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.

“The results in men are better than women. [The study] tries to explain it by size, but I don’t think that’s a complete explanation,” Dr. Su continues.

He says he feels more research is needed in this area to better answer this question.

Some Devices Have Higher Failure Rates

As studies have noted higher failure rates with certain kinds of hip resurfacing systems, one proposed explanation for the differences was that surgeons weren’t adequately trained to work with them.

But the Australian study refutes that notion, with analysis showing higher failure rates associated with certain kinds of components, regardless of the surgeons’ training and experience with them.

After 11 years, the Australian study found that of the three most commonly used implants, the ASR and the Durom have a significantly higher risk of revision than the Birmingham hip resurfacing system.

The ASR hip resurfacing system has recently been taken off the worldwide market, and DePuy, the company that makes the implants warned doctors this week about the possibility of early failure rates.

And in July 2008, Zimmer, the company that makes the Durom parts, said that it would temporarily halt sales of that product in the U.S. while they offered doctors additional training.

The Durom system has been implanted in patients in the U.S. in clinical trials, The Food and Drug Administration (FDA) has not yet approved it for general use. 

Dr. Della Valle says this research can be confusing to patients and in the end, he believes, the choice between a total hip replacement and hip resurfacing depends more on the individual than anything else.

“It really has to be somewhat customized in terms of what the patient wants because there are some very active 65-year-olds who want to run and do sports, and if their bone quality is good, I think they could be a candidate for hip resurfacing,” Dr. Della Valle explains.

“I would hate to see the technology written off, because it works well in some patients, and those are some of my happiest patients,” he continues. “But for the majority of patients, a conventional total hip replacement will be associated with a lower risk of complications and problems than resurfacing. But there is a segment of the population that benefits from the technology and has an equivalent or lower risk of revision.”

How Components Are Secured Also Affects Implant Survival

In a second study, researchers in Finland, drawing on data from that country’s joint replacement registry, found that the way components are applied to the bone – either with or without cement adhesives – appears to affect the lifespan of total hip replacements in younger patients.

They studied 4,032 cases of primary total hip replacements done on patients younger than age 55 with osteoarthritis. They found groups that had used so-called cementless stems had an 89 or 90 percent survival rate compared to cemented stems at 72 percent. Cementless cups had an 80 percent survival rate compared to 71 percent for cemented cups.

“It shows that cemented fixation is no longer the gold standard. We think we knew it but it’s nice to have confirmation,” Dr. Su says. “It continues to show that this age group, the younger age group, is challenging and we need to continue to prove outcomes in that age group.”

Dr. Della Valle agrees and says he finds these results interesting because most European countries have continued to use cemented procedures. But about 15 years ago he says most North American surgeons shifted from cemented to cementless, finding the technique easier and believing it gave the implant more flexibility.

“In North America it was a very rapid switch from cemented to cementless,” Dr. Della Valle says. “It was really almost a wholesale overnight switch, and it’s comforting to know that now there’s data from outside the U.S. that suggests that’s a good decision.”