WASHINGTON - Doctors are beginning to offer a new alternative to hip replacement, one aimed at younger, athletic baby boomers who've worn out their joints too soon. Now they no longer have to wait until they hit their 60s for a fix.

A traditional artificial hip is seen on the left and the Birmingham hip is on the right in this June 14, 2006, photo taken at Barnes-Jewish hospital in St. Louis.[AP]

It's called hip resurfacing, covering a damaged hip's ball and socket with smooth metal rather than cutting away worn bone and replacing it.

The operation hit the US market last spring with Food and Drug Administration approval of the British-designed Birmingham Hip Resurfacing System. Competitors are in clinical trials here, and expected to clear FDA later this year.

It's not the first time orthopedic surgeons have tried resurfacing worn-out hips. But where earlier attempts failed, data from Europe suggest this latest approach uses longer-lasting materials - with the additional promise of a joint that may hold up to the heavy recreation of today's 40- and 50-somethings better than traditional hip implants.

"I do have people that call me and say, 'My father had hip resurfacing in 1970 and it didn't work. Why are we doing that now?'" says Dr. Michael J. Anderson, an orthopedic surgeon in Milwaukee who estimates that about 15 percent of his hip implants now are resurfacings.

His response: Comparing today's resurfacing with yesteryear's is like comparing a modern car to a Model T.

Not everyone's a good candidate, specialists caution. Resurfacing isn't for patients with thinning bones - part of the joint could break - or those who have poorly functioning kidneys that can't eliminate microscopic metal particles produced when the joint's reinforced pieces rub together.

Moreover, while patients typically recover quickly, resurfacing is harder to perform than a hip replacement, and only a small fraction of the nation's orthopedic surgeons so far are trained to do it.

But interest is growing, as evidenced by a focus on hip resurfacing at next month's annual meeting of the American Academy of Orthopaedic Surgeons - and a growing demand for hip repair from ever-younger patients.

Until now, "you might have told someone to soldier on for as long as you possibly can," because a standard hip replacement before age 60 is itself likely to wear out, explains academy spokesman Dr. Scott Rubinstein, of the Illinois Bone and Joint Institute.

With the new resurfacing option, "people may be a little more aggressive" in treating younger creaky joints, he adds.

More than 400,000 total or partial hip replacements are performed each year, a number growing as the population ages.

Typically, surgeons replace a hip by cutting off the femoral head, the joint's ball, and replacing it with a metal ball mounted on a rod implanted deep in the thigh bone. A plastic socket replaces the original. Those artificial hips can bring tremendous relief to people crippled by hip pain.

But the metal-on-plastic friction means the implants can begin wearing out in about 15 years, sooner if sports or other activities increase pressure on the joint. For the average 65-year-old, that's no problem. A 50-year-old, in contrast, could very well wear out an initial replacement and have little thigh bone left to fit another.

"You're dealing with Swiss cheese," is how hip replacement pioneer Dr. Mitchell Sheinkop describes the remaining bone.

Enter resurfacing. Surgeons lightly shave the damaged femoral ball and fit a metal ball snugly over it. That ball rolls in a metal cup reinforcing the socket. The idea: Metal-on-metal shouldn't wear out as fast, and if patients do need another replacement in 15 or 20 years, the thigh bone is largely intact.

"This resurfacing initiative has interest because we're sparing bone," explains Sheinkop, a Rush University professor and joint replacement director of the Neurologic and Orthopedic Institute of Chicago.

What's the evidence? The FDA cited studies showing the Birmingham Hip resurfacer lasted at least five years, approving its sale on condition that manufacturer Smith & Nephew Inc. continue tracking its endurance for 10 years.

Doctors differ on what age is the cutoff for resurfacing, somewhere between 60 and 65, largely dependent on the patient's bone strength. Nor do all insurers cover it. The implant costs about 20 percent more than a standard artificial hip, adding to the $35,000 tab.

Complicating the choice is that surgeons call newer artificial hips - ceramic-on-ceramic balls and sockets, or tougher plastic designs - good options for even the most active person just turning 60.

So resurfacing is emerging as a niche for the younger sports enthusiast. Dr. Marc Wiener, a Chicago-area internist, chose resurfacing when his own hip degenerated in his 40s, because it came with few restrictions on his activity. Wiener exercised before surgery to be in prime condition for physical therapy afterward - and played 18 holes of golf a month after his resurfacing, hit the basketball court at seven weeks and the tennis courts in three months.

Milwaukee's Anderson cautions that average patients shouldn't expect as much. "If you find your exercise level can increase, we like that, but I'm not going to promise you'll be playing doubles at Wimbledon next year."