A Future Reset: After losing his arm in an I.E.D. explosion in Afghanistan, Cpl. Sebastian Gallegos has adjusted to his prosthetic limb.

SAN ANTONIO — After the explosion, Cpl. Sebastian Gallegos awoke to see the October sun glinting through the water, an image so lovely he thought he was dreaming. Then something caught his eye, yanking him back to grim awareness: an arm, bobbing near the surface, a black hair tie wrapped around its wrist.

The elastic tie was a memento of his wife, a dime-store amulet that he wore on every patrol in Afghanistan. Now, from the depths of his mental fog, he watched it float by like driftwood on a lazy current, attached to an arm that was no longer quite attached to him.

He had been blown up, and was drowning at the bottom of an irrigation ditch.

Two years later, the corporal finds himself tethered to a different kind of limb, a $110,000 robotic device with an electronic motor and sensors able to read signals from his brain. He is in the office of his occupational therapist, lifting and lowering a sponge while monitoring a computer screen as it tracks nerve signals in his shoulder.

Close hand, raise elbow, he says to himself. The mechanical arm rises, but the claw-like hand opens, dropping the sponge. Try again, the therapist instructs. Same result. Again. Tiny gears whir, and his brow wrinkles with the mental effort. The elbow rises, and this time the hand remains closed. He breathes.

Success.

“As a baby, you can hold onto a finger,” the corporal said. “I have to relearn.”

It is no small task. Of the more than 1,570 American service members who have had arms, legs, feet or hands amputated because of injuries in Afghanistan or Iraq, fewer than 280 have lost upper limbs. Their struggles to use prosthetic limbs are in many ways far greater than for their lower-limb brethren.

Among orthopedists, there is a saying: legs may be stronger, but arms and hands are smarter. With myriad bones, joints and ranges of motion, the upper limbs are among the body’s most complex tools. Replicating their actions with robotic arms can be excruciatingly difficult, requiring amputees to understand the distinct muscle contractions involved in movements they once did without thinking.

To bend the elbow, for instance, requires thinking about contracting a biceps, though the muscle no longer exists. But the thought still sends a nerve signal that can tell a prosthetic arm to flex. Every action, from grabbing a cup to turning the pages of a book, requires some such exercise in the brain.

“There are a lot of mental gymnastics with upper limb prostheses,” said Lisa Smurr Walters, an occupational therapist who works with Corporal Gallegos at the Center for the Intrepid at Brooke Army Medical Center in San Antonio.

The complexity of the upper limbs, though, is just part of the problem. While prosthetic leg technology has advanced rapidly in the past decade, prosthetic arms have been slow to catch up. Many amputees still use body-powered hooks. And the most common electronic arms, pioneered by the Soviet Union in the 1950s, have improved with lighter materials and microprocessors but are still difficult to control.

Upper limb amputees must also cope with the critical loss of sensation. Touch — the ability to differentiate baby skin from sandpaper or to calibrate between gripping a hammer and clasping a hand — no longer exists.

For all those reasons, nearly half of upper limb amputees choose not to use prostheses, functioning instead with one good arm. By contrast, almost all lower limb amputees use prosthetic legs.

But Corporal Gallegos, 23, is part of a small vanguard of military amputees who are benefiting from new advances in upper limb technology. Earlier this year, he received a pioneering surgery known as targeted muscle reinnervation that amplifies the tiny nerve signals that control the arm. In effect, the surgery creates additional “sockets” into which electrodes from a prosthetic limb can connect.

More sockets reading stronger signals will make controlling his prosthesis more intuitive, said Dr. Todd Kuiken of the Rehabilitation Institute of Chicago, who developed the procedure. Rather than having to think about contracting both the triceps and biceps just to make a fist, the corporal will be able to simply think, close hand, and the proper nerves should fire automatically.

In the coming years, new technology will allow amputees to feel with their prostheses or use pattern-recognition software to move their devices even more intuitively, Dr. Kuiken said. And a new arm under development by the Pentagon, the DEKA Arm, is far more dexterous than any currently available.

But for Corporal Gallegos, becoming proficient on his prosthesis after reinnervation surgery remains a challenge, likely to take months more of tedious practice. For that reason, only the most motivated amputees — super users, they are called — are allowed to undergo the surgery.

Corporal Gallegos was not always that person.

His father, an Army veteran, did not want him to join the infantry, but it was like him to ignore the advice.

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Source: http://www.nytimes.com/2012/11/27/us/prosthetic-arms-a-complex-test-for-amputees.html?pagewanted=1&ref=technology