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Computer Chip Gives Prosthetic a 'Leg Up' - 2002-11-15


Each year, some 200,000 Americans lose a limb, through accident or disease. Nearly three-quarters of those new amputees have lost a leg. Many choose to wear a prosthesis, an artificial leg. While advances in prosthetic design have helped make it possible for them to run, dance and even play sports again, simple tasks like walking down stairs can remain difficult and cumbersome. But new technology is changing that, as well.

Hundreds of artificial legs are made each year in the basement of Texas Scottish Rite Hospital for Children in Dallas. They're sculpted by hand from plaster of Paris. And, with special cosmetics, they can look just like a natural leg.

"This one has the horse tattoo. Someone must be a horse fan..."

But Scottish Rite's Director of Prosthetics, Don Cummings, says the latest development in his field isn't a leg that looks natural, but rather a leg that moves naturally. The C-Leg actually thinks for itself, thanks to a tiny microprocessor imbedded in a hydraulic knee. The letter "C" stands for the computer language that makes it work. "It's controlling the way the knee swings and the way the knee would react to stumbling or sudden changes in motion. Just like your hamstrings and quadriceps act to control your knee when you're walking," he says.

Mr. Cummings says sensors in the metal knee and ankle detect sudden changes in torque, like when an amputee walks on an uneven surface or is bumped into. Then, the computer chip makes nearly instantaneous adjustments to stabilize the leg and prevent the knee from buckling. That means amputees are less likely to fall and injure themselves.

That was a frequent problem for 17-year-old Eric Finger of Dallas, who lost both his legs after he contracted a form of meningitis. "I use this one type of knee that would just bend whenever you put weight on the toe, but that one didn't work out too well because whenever I'd just be standing there, if I put any weight on the toe, sometimes it would just unlock and I'd just fall down, just standing there," he says.

But earlier this year, a private patron bought Eric one of the $40,000 C-Legs. A software program helped encode the leg to fit Eric's personal settings, like height, weight and mobility. The C-Leg, with its titanium shaft, is heavier than most prostheses, so Eric, like most owners, didn't add the weight of a cosmetic shell to make it look like a natural leg.

But now, he says, he rarely loses his balance and can more easily manage the daily tasks his peers take for granted. "One thing that's really neat is being able to go down stairs, actually walk down them and not one foot at a time, just 'cause going down stairs one foot at a time, it's kinda embarrassing 'cause you slow everybody down, but with the C-Leg it's not a problem, I can just go down them," he says. "Same with slopes and any kind of terrain, really."

As he grows comfortable with his new C-Leg, Eric can change its settings just by tapping his toe, so he doesn't have to adjust the knee mechanically before he tries to rollerblade, ski, or ride a bike. He still wears a standard prosthesis on his right leg because it was amputated below the knee.

Jokingly called the Porsche of prostheses, the C-Leg was developed by a German company five years ago. It's been available in the United States since 1999. And Eric Finger is one of only 1,500 or so Americans who have one.

Prosthetist Gary Stroble, who fits and sells the C-Leg, says its hefty pricetag prevents more amputees from buying one. "It is expensive at this point," he says. "However, I feel like the more and more that it's utilized, the price should go down and we may get some other microprocessor knees that would be in competition with it."

Since the C-Leg is electronic, it has to be recharged every night. Isn't a good choice for amputees who work near water, since it can't get wet. And while the C-Leg helps amputees walk down stairs, it doesn't make it any easier to climb them. Still, Mr. Stroble believes the C-Leg represents a new direction for prosthetic legs. And its technology may even spur new applications for paraplegics, slowly blurring the line between man and machine.

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