What was left of Dan Sivia's ankle simply didn't work. He limped through his 30s by sheer force of will, one foot almost completely immobile from repeated broken bones and surgeries. Then a doctor offered his last hope: An ankle replacement. A what? Sivia knew about hip, knee, even shoulder replacements. But ankles?

His confusion is understandable: The first ankle replacements of the 1970s were abandoned when they couldn't withstand the pounding of daily life. A second generation in the '90s lasted longer but never became really popular.

Now the nation is embarking on a new generation of artificial ankles designed to work more like the joint you're born with, a move specialists hope finally will offer less pain and more function to thousands who hobble — although it's too soon to be sure.

"These third-generation prostheses really mimic a natural ankle, which is really what makes them different," says ankle specialist Dr. Steven L. Haddad of the Illinois Bone and Joint Institute and an orthopedic surgery professor at Northwestern University.

If the newer implants pan out, it's a market ripe for growth. More than 200,000 people seek care for ankle pain annually, with few options for the severely damaged. More than 8,000 a year get their ankle bones fused, a last-ditch treatment after years of suffering, while surgeons perform between 2,000 and 2,500 ankle replacements.

While Medicare pays for ankle replacements, which Haddad says can reach $50,000 including a three- to five-day hospital stay, many other insurers don't. And a review in September's Journal of the American Academy of Orthopedic Surgeons cautions that so far, there is little research to tell how long newer versions will last — and that few hospitals have much practice in implanting them.

But for Sivia, the surgery restored an ability to walk that the 39-year-old thought he'd forever lost. His leg was crooked from a series of breaks that began in childhood and included a crushing ankle fracture at 28. A decade of pain later, he sought out Haddad. Then he spent 17 months on crutches, with external pins holding bones in place, as Haddad rebuilt his leg. The last surgery, the ankle implant, came in July.

"When I got to rake my own lawn — I've done it three times just because I can," the Waukegan, Ill., man said with a laugh. "I'm riding my bike, I'm doing all the things everybody else is doing."

Haddad says ankle sufferers tend to move like a sidewinder snake, one foot gingerly turned out to the side while the other foot does the heavy pushing to walk. They might have standard arthritis. But usually, fractures from years earlier — sometimes broken ankles, but often broken legs that left the entire lower limb out of alignment — simply made the ankle and its cushioning cartilage wear out.

Fusion — eliminating the pain-causing friction by permanently connecting ankle bones so they won't move — is usually an easy operation, with about 5 percent who fail to heal. The disadvantage is a stiff ankle that limits the foot's range of motion and eventually causes a domino effect, wearing out smaller joints in the foot to cause more pain until they, too, are fused.

Hence the quest for artificial ankles that would allow a fully flexible foot and normal gait.

That's not an easy task. The ankle joint is smaller than the hip and knee and must absorb more force than its sister joints, Dr. Keith Wapner of the University of Pennsylvania told a recent American Academy of Orthopedic Surgeons meeting.

The Food and Drug Administration began clearing so-called third-generation ankle implants in 2005, versions that Wapner expects to last longer. Each model is slightly different but consists of two attached parts. Surgeons drill a tunnel into the lower leg bone and slide in the stem of the artificial joint. A bottom piece connects to the top of the foot. Thin plastic hooked to one side functions as cartilage. Bone then grows into the implant, holding it in place.

In Europe, doctors also can use a similar but three-piece artificial ankle, where the plastic cushion is free-floating. Amid questions about whether that approach is better or worse, the FDA is evaluating whether to allow it here.

So which is better, fusion or replacement?

It all depends on age and activity. Even if these new ankles last more than a decade as Haddad expects, someone who jogs or mountain climbs will wear theirs out faster than someone who is sedentary. Also, different patients have different risks of wound infections.

"If you're someone that does not mind having additional surgeries on your ankle in the future as a trade-off to get better function, then a replacement is a better option," Haddad tells patients. "If you want to take care of it once, you have to opt for a fusion."