Aimed at younger patients who want to delay total hip replacement, this procedure removes only the damaged joint surfaces. The socket is replaced with a metal cup and the femoral head is shaved down and covered by a metal cap anchored by a short stem. That preserves more of the thighbone, making future revision surgery easier.

"Patients read marketing materials and want this procedure," says John Callaghan, M.D., second vice president of the American Academy of Orthopaedic Surgeons. "But the appeal of preserving bone can lead to false expectations."

Women who had resurfacing are twice as likely to need early revision than those receiving regular hip implants, chiefly due to femoral neck fractures, according to a 2008 review by the Royal College of Surgeons of England. Women might be at higher risk for such fractures because their bones are smaller and weaken at menopause.

Additional concerns include the complexity of the operation and metal-on-metal debris. Some surgeons avoid the procedure altogether, others recommend it only for younger men, and some propose it for strong-boned patients regardless of gender. But most agree that resurfacing is not advisable in patients who are likely to have weak bones—such as postmenopausal women, people over age 65, or those who score poorly on bone-density tests.