For a growing number of patients, resurfacing a degenerative hip joint is an alternative to replacing it entirely. The essential difference between a hip resurfacing and a hip replacement is the preservation of bone in the femur.
"Our typical patients are people in their 40s and 50s who still want to play tennis or ride a bicycle, or even younger people who have developed a degenerative hip early in life," says Thomas Parker Vail, M.D., chair of Orthopaedic Surgery at UCSF Medical Center.
Patients are very interested in a procedure that will allow them to remain active and preserve options for future reconstruction, if needed. Hip replacements can wear out over time and second surgeries may be complicated once bone has been removed during an earlier procedure. Resurfacing, with a larger, closer to natural ball-and-socket size, poses less risk of dislocation than the typically smaller ball and socket used in hip replacement.
The current generation of metal-on-metal resurfacing implants—which mate a cementless, porous socket with a cemented head—has been in use for almost a decade in the United Kingdom and Australia. The ball is capped and the socket is lined with chrome-metal alloys. Since 2006, two implants have been approved for clinical practice in the United States and more are on the way.
There are no long-term data to quantify the durability of the new resurfacing implants. Vail has participated in clinical trials of two different resurfacing implants, starting in 2000, and he has been active in the design of new implants. "We still choose candidates very carefully," he says. "It's too early to say we have defined and understand all potentially adverse outcomes—but our early experience has been very positive."
Patients with osteoporosis, cysts or fragmented bones are not candidates for resurfacing, as the implant is more likely to fail. Patients who are allergic to the metal alloys used for resurfacing—chromium, cobalt, nickel and iron—also should forgo surgery. Hip resurfacing provides only limited opportunities to correct structural abnormalities, Vail notes. If a goal of surgery is to correct leg length differences or to reposition the joint, then hip replacement is the appropriate choice.
Hip resurfacing poses a small risk for femoral neck fracture, early implant loosening and exposure to metal ions. Research by Vail and others indicates that greater surgical experience minimizes risk. "Even in the best-case scenario with the most experienced surgeons, fractures of the hip below the hip resurfacing will still occur in a certain percentage of patients—it appears to be 1 to 2 percent," he says.
The surgical approach should be respectful of soft tissue attachment of the bone and try to preserve blood supply, he adds. "My preference is to use the posterior approach. I feel I can protect the gluteal muscles, and it's an approach that heals nicely and gives outstanding functional results."
In a recent clinical research study, Vail and collaborators compared outcomes for hip replacement with those of hip resurfacing for young, active patients. The study found that two years after surgery, complication rates were no different. Hip resurfacing patients had a slightly greater range of movement and a higher activity level, on average—meaning that they were testing the implants more. However, there is no proof that replacement implants are any more vulnerable than resurfacing implants to the wear and tear of high activity levels, Vail says.
A new generation of resurfacing implants is an exciting development in hip surgery. Not all patients are suited to this bone-conserving surgery. Success is predicated upon excellent surgical technique and good-quality bone. In general, the best candidates are:
Thomas Parker Vail, M.D., can be contacted at (415) 353-2808.
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