New prosthetic arm born from Star Wars

12:10 PM, Mar 12, 2012   |    comments
The Luke Arm prosthetic, shown during testing at Walter Reed National Military Medical Center in Bethesda, Md., allows for fine motor movement and grasping objects such as a drill and snow shovel.
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In the movie "The Empire Strikes Back," Luke Skywalker's hand is severed in a battle with Darth Vader and replaced by a futuristic prosthetic. Now science fiction is becoming science fact as the Defense Department funds the development of the "Luke Arm," which may replace limbs that veterans have lost in battle.

The lifelike arm, developed under a Defense Advanced Research Projects Agency contract awarded to New Hampshire-based Deka Research and Development, has undergone more than 4,000 hours of testing, largely in clinical trials at Veterans Affairs Department sites around the country.

"We did a lot of studies not just at Deka but with the VA," said Dr. Stewart Coulter, Deka's general manager. "One of the best things about that is that it gives us more insight and feedback into our wounded warriors, more feedback about how they want to use the arm system."

Air Force Tech. Sgt. Joe Deslauriers wowed onlookers at the Military Health System conference outside Washington, D.C., last month when he opened and closed his "hand" and wiggled the fingers. Deslauriers, who lost his legs and part of his left arm to a roadside bomb in Afghanistan, was fitted with the Luke Arm.

Deslauriers, with some help, removed the arm and showed off small sensors inside it that respond to the movement of muscles in his vestigial limb, which ends below his left elbow.

The arm is being developed as part of DARPA's Revolutionizing Prosthetics program, which began in 2005. It is intended to be a fully functional "strap-on-and-go" prosthesis.

Coulter said developers simultaneously took aim what they saw as the three problem areas in most prosthetic arms: range of motion, control schemes and sockets.

"These are the three issues that needed to be solved," he said. "If you design an arm which can pick up a gallon of milk, lift it up over your head, it doesn't do any good if the socket of the arm falls off you."

Prosthetic arms typically have two to three degrees of freedom: a hand opening and closing, an elbow bending or a wrist rotating. Most arms have low torque and provide no feedback to the user, Coulter said, adding that the Luke Arm can have up to 10 degrees of freedom - two each in the shoulder, elbow and wrist, and four in the hand - depending on the user's needs. Its hand has several different grasps, and the arm can reach over the user's head or behind his back.

Control schemes in many advanced prosthetic arms are sequential. To move the arm, one must first move the elbow, then the wrist, and then open and close the hand, as opposed to fluidly moving several joints at once. The Luke Arm utilizes foot controls that work simultaneously with controls in the socket.

Sockets typically are enveloping and tend to generate heat, which can make users uncomfortable.

The Luke Arm's socket is designed to grip tightly when the user is holding something heavy and relax when they're relaxing - watching TV or sitting at their desk.

The system also provides feedback through the socket to the vestigial limb to let the user know, for instance, how hard they are grasping an object. The grips allow for fine movement or grasping an object like a drill.

"You haven't seen a person's face light up until you see someone who hasn't used a drill in 20 or 30 years use a drill," Coulter said. "It's a pretty neat process."

One of the toughest engineering challenges was finding a way to control the system, because there were more degrees of movement than ways to provide that control. The project has developed foot controls that respond to the tilting of a foot to make the hand make complex motions forward, backward, up, down, left and right.

"Does this work perfectly all the time? No, it's not something you'd use when you're walking," Coulter said. "But if you're sitting or standing, you get a pretty good level of control."

The effort has not simply involved engineers but incorporated input from people who would use such a system. Coulter said the team performing clinical studies at VA sites worked with people of both genders and various ages to get feedback about what worked and what needed improvement.

Coulter showed pictures of Deka's "test pilots" - people using the arm while shoveling snow, putting on socks and using a screwdriver.

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