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When a patient's hip fails him, damaged by osteoarthritis, necrosis, a fracture, an infection or other conditions to a point at which rehabilitation is beyond the control of medication, a common solution in recent decades has been to undergo total hip replacement. In the past few years, however, a newer option - and, some say, a more effective alternative - has emerged in hip resurfacing surgery.
"Resurfacing is a very conservative type of hip replacement," says Michael A. Mont, MD, director of joint preservation and reconstruction at the Rubin Institute for Advanced Orthopedics in Baltimore; he has performed the procedure more than 1,200 times since its development in the late 1990s and currently does about 200 a year. "It's analogous to a dentist capping a tooth."
The procedure is not without its skeptics, though. "The complications of this operation outweigh any possible advantages," says Paul F. Lachiewicz, MD, professor of orthopedics at the University of North Carolina School of Medicine in Chapel Hill, N.C. "I think people have underestimated what the problems are going to be in the future."
How resurfacing works
In traditional total hip arthroplasty, a surgeon removes the head (or ball) and neck of the femur, replacing them with a titanium implant. Bone is also removed from the acetabulum and a polyethylene socket in a titanium shell is cemented into the pelvis.
Total hip replacement is believed to be most effective among elderly and sedentary patients, the demographic that is most likely willing to adopt a decreased schedule of activity after the surgery. Clinical experts warn that it isn't a permanent fix and isn't intended to last an extended lifetime, since the polyethylene surface may wear down. Younger patients especially may suffer joint loosening, joint dislocation or bone loss over time, complications which may require another surgery.
In contrast, hip resurfacing, as its name suggests, largely builds on a patient's pre-existing anatomy. The femoral head is reshaped, not removed, and covered with a cobalt chrome ball on a stem that is inserted into the bone. Damaged or diseased bone and cartilage are shaved from the pelvic socket and a cobalt chrome shell is implanted within it. Hip resurfacing's proponents say patients may experience shorter recovery times than hip replacement patients - after a short hospital stay, six weeks to three months instead of three months to six months - due to the more conservative treatment.
Resurfacing's resulting patient outcomes also show an improvement over those of total replacement, says Dr. Mont. "I get more motion with resurfacing than with regular hips," he says. "I get patients who feel more normal with resurfacing." While he acknowledges that joint feeling is a quality both subjective and difficult to prove, he adds that a survey he's conducted suggests that replaced hips serve post-op patients very well, but "don't approach normal."
Since resurfacing uses a metal-on-metal device as opposed to replacement's metal-on-plastic bearing, its hardware has proved more durable in the long term and less likely to loosen. "Metal-on-metal devices have very low wear rates," says Dr. Mont. "Theoretically, they can last 20 to 30 years." Also, "because [the resurfacing component] has a large femoral head and matches the femoral head of patients within a millimeter or two, the chance of dislocation is lower," he says.
The procedure's preservation of bone mass benefits the patient in the event that subsequent surgeries are necessary. "If, God forbid, you should be in an auto accident that fractures your hip and you need revision surgery, there's still bone there," says Dr. Mont. "You can never go from a hip replacement to a resurfacing, but you can go from a resurfacing to a replacement if you need to."
At present, the technology and hardware employed in the procedure are commercially marketed by only one manufacturer, Smith & Nephew, whose Birmingham Hip Resurfacing System received FDA approval last May. Several other implant manufacturers, including BioMet, DePuy, Stryker, Wright Medical Technology and Zimmer, have devices currently undergoing clinical trials or awaiting FDA approval.
Proceeding with caution
"Do you realize that this is the third attempt at resurfacing?" asks Dr. Lachiewicz. An early attempt in the 1970s blamed its failure on the cementing of the components, he says, and a second attempt a decade later found little success with a metal-on-plastic joint. While the jury's still out on the third try, he remains skeptical. "We don't yet have a 10-year follow-up," he notes. The procedure has been performed for 10 years, but it also saw changes in the first few years in response to early difficulties. "No one's standing on their work from eight to 10 years ago," he says.
At the American Academy of Orthopaedic Surgeons' 2006 annual meeting, which was held more than a month before the FDA issued its approval, Dr. Lachiewicz argued the counterpoint view in a pair of presentations titled "Resurfacing Arthroplasy: Time to Consider It Again?" He was invited to make the case a second time - against more than one of the procedure's proponents this time - at this year's academy meeting in San Diego last month.
Dr. Lachiewicz says his objections to the procedure involve the following five concerns: the premise for its use, its limited patient population, its learning curve, its possible complications and its metal-on-metal device.
One stated premise for resurfacing, he notes, was that early total hip replacement components were prone to loosening and dislocation; but he points out that the actual data from those procedures show a low rate of failure. He also takes issue with the procedure's characterization as conservative as "more hype than reality," since it isn't minimally invasive and can involve more OR time, more bleeding and more bone removal from the socket even as it preserves bone mass on the femur.
He also questions how many patients suffering from diseased or damaged hips are actually suitable candidates for the surgery. Optimal eligibility criteria is defined as patients who are young, active men; who suffer from osteoarthritis only; who have a body mass index of 35 or below; whose legs are within one centimeter of the same length; and whose femurs are of a particular shape. "When you think about it," he concludes, "there's a very limited number of patients for whom this procedure is the right thing to do." In his own practice, he says, less than 10 percent of his hip patients would qualify.
The steep learning curve that surgeons must climb in order to master the procedure also tends to limit resurfacing's availability, says Dr. Lachiewicz. "The techniques for doing this are much more difficult for surgeons than those of conventional hip replacement," he says, since surgeons need to obtain acetabular exposure without removing the femoral head and neck and since proper component insertion requires delicate precision. Citing a study by Dr. Mont, who counted 11 femoral neck fractures and two revisions among his first 50 resurfacing patients and one fracture and one revision among his second 50 patients, Dr. Lachiewicz questions how long it will take the average orthopedic surgeon, who performs 10 hip surgeries a year, to acquire the necessary skills.
Resurfacing surgery doesn't offer a significantly lower incidence of complications such as femoral neck fracture, infection, dislocation, early osteolysis and heterotopic ossification, says Dr. Lachiewicz, and adds another concern. "I have major concerns with metal-on-metal in joints," he says. Resurfacing patients have been observed to have elevated blood and urine ion levels as a result of the device's composition and "those [levels] never seem to go away," he says.
"A lot of orthopedic surgeons feel pressure to do resurfacing," says Dr. Lachiewicz. "They feel pressure from their patients and the community." More and more medical advances are marketed directly to patients with big promises, he notes, and while successful outcomes are often possible, they aren't delivered across the board, especially when they rely on technique. "Anybody can give a pill and get the same results, but surgery is more difficult to reproduce."
Dr. Mont acknowledges many of Dr. Lachiewicz's concerns as valid points, but also argues that they're not insurmountable obstacles.
"There is a learning curve," he admits. "I had more problems at the beginning. You need to do a few of these before you get good at it." Though it's a technically challenging operation, not every surgeon will need 50 cases under his belt to master the procedure, in large part because they'll learn from surgeons who've already overcome the major difficulties. "The learning curve should be about four or five [cases] now," he says.
In his own practice, he's found that as many as 20 percent of hip patients are able to undergo resurfacing surgery with optimal results. One out of every five potential patients is not a prohibitively limited pool, he notes. It's true that resurfacing doesn't have a lower incidence of complications than replacement does, he says, but he's found that when an experienced surgeon performs both procedures, the possibility of such risks should be the same. And while "we do not know the significance of" the increased ion levels resulting from the metal-on-metal joint, "the good news is, those rates have not spiked over the past eight years" and no cancers or toxicities have been traced to them, he says.