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Prosthetic offers realistic feeling, grip

When Army Sgt. Juan Arredondo catches a football while playing with his kids, it seems even more miraculous than the New York Giants’ recent Super Bowl win.

Arredondo, 28, lost his left hand when a roadside bomb exploded near his Humvee in Ramadi, Iraq, on Feb. 28, 2005, severing his arm at the wrist.

Video

See the i-LIMB in action

“My hand was still on the steering wheel, so I grabbed it and got out,” Arredondo said. He stuck his hand in his cargo pocket, but when he presented it to the doctors back at the combat support hospital at Taqaddum, they couldn’t save it.

Scientists built him a new one.

Arredondo is the first soldier to use a new hand — the i-LIMB — that has working motors in each finger. Previous versions had only one motor that powered the thumb and two fingers.

“When they let me try it, I was like, ‘Wow, I look just like the Terminator,’ ” Arredondo said. “It’s made a big difference. There are no superpowers in the hand; it just makes life more normal.”

With his first prosthetic hand, he could move it so it formed a “C” in a pinching movement.

“That’s all it could do — just open and close,” he said. “Now, I can make a fist or wrap it around a baseball. The best part is, I can pick up my kids more naturally — under the armpits.”

In a video demonstrating the hand, he interlaces the fingers of both hands, using the mechanical fingers to emphasize points as he talks. He extends and contracts them just as he does his natural hand. The electronic hand moves gracefully, though it looks a little surreal, as if light passes through the synthetic “skin” stretched over plastic bones. That’s because the skin is semi-transparent.

The hand picks up electrical signals transmitted by the muscles in his arms to electrodes on the outside of his skin.

“Myoelectric signal has been around for a while,” said Phil Newman, head of marketing for Touch Bionics, the developer of i-LIMB. “We’re just using it with new technology.”

Newman said the idea of five working fingers became feasible after scientist David Gow created a fixed gear box that fits in the knuckles of each finger, allowing a motor to operate from the long parts of the finger.

Before, the technology was too heavy, but the new hand is made of a strong, lightweight plastic similar to what is used in cell phones.

“It weighs about the same as the old devices, which weigh less than a human hand,” Newman said. “That’s heavier than you’d think.”

A smaller hand is available for women. By the end of the month, 130 people will be using it, he said. It costs between $50,000 and $60,000, and has been on the market since July.

“The hand moves and looks very much like a human hand,” Newman said. “The psychological benefit is important — it’s quite an emotional reaction for them.”

For example, a Vietnam vet had been using a hook-and-grasp device. It doesn’t look like a hand, and the man felt uncomfortable meeting new people because he couldn’t shake hands without immediately pointing out his disability, Newman said.

Then, he was fitted with the i-LIMB. “This guy was just walking around grinning and shaking hands with everybody,” he said.

i-LIMB specialists chose Arredondo as one of their first users because after the explosion that took his real hand, he always wore his prosthetic device, Arredondo said. A lot of people who lose limbs wear the prosthetics only part of the time.

Arredondo, who works as a benefits liaison for the Wounded Warrior Project, a nonprofit group that helps severely wounded service members and veterans, said he flexes the inside muscles of his forearm to close the hand, and the outside muscles to open it. If he holds it for two seconds longer, he can move the thumb — which rotates 90 degrees.

“I can contract it as slowly or fast as I want,” he said. “I can pick up an egg without even thinking about it.”

It took a little while to figure out how tightly he should close the hand so as not to squash the egg, or a paper cup — or a human being.

“I can shake somebody’s hand without crushing it,” he said, laughing.

He’s gotten so good with it that he works on cars, goes rock-climbing and lifts weights.

“I can play sports with my kids,” he said. “I can catch a football — but I’m still working on letting go of it.”

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