Building a Better Limb
Veterans are inspiring a big push to create thought-controlled prosthetics
The Army, which in past wars automatically discharged amputees, now lets them return to active duty once they're fit. Sgt. George Perez, a 23-year-old from Carteret, N.J., redeployed to Afghanistan as a paratrooper with the 82nd Airborne Division last year, despite having lost his left leg to a roadside bomb in 2003.
Soldiers who lose an arm in battle find themselves with less appealing options. Jonathan Kuniholm, who served as a marine in Iraq and lost his right arm below the elbow 19 months ago in an explosion, finds himself very frustrated with his state-of-the-art "myoelectric" arm, which is controlled by sensors on his own arm that read muscle contractions. "The hand can open and close, and you can rotate the wrist. But you can't do those simultaneously," Kuniholm says. Even the simplest action--picking up a pitcher and pouring water--becomes a tedious multistep process, so he often reverts to a Captain Hook-style hook. Now a biomedical engineering graduate student at Duke University, Kuniholm, 34, of Durham, N.C., is well aware of existing technologies in robotics and control systems that could be assembled into "something much more useful than what we have now."
Almost real. His wish for that arm may soon come true, thanks to the resources of the Defense Department. "When you look at what your natural hand does, it's really quite extraordinary. It's probably the most complex tool in all of nature," says Col. Geoffrey Ling, a neurologist who directs the Revolutionizing Prosthetics projects for the Defense Advanced Research Projects Agency. If Ling has his way, the arm now in development will be as flexible and attractive as a real arm. It will sense the weight and texture of objects, give the wearer a "feel" for what the arm is doing, and be able to make 22 independent motions, as opposed to the three in current prosthetic arms. Two big players in experimental engineering--Johns Hopkins University's Applied Physics Laboratory and DEKA Research & Development Corp. in Manchester, N.H., home of the Segway--were chosen to develop arms; DEKA's is to be ready for clinical trials and approval by the Food and Drug Administration by 2007, APL's by 2009.
The mechanical challenges are daunting, but the engineers and physicians leading the projects say that what really keeps them up at night is the problem of control. "I want an arm where the patient can play the piano," Ling says. "We're not talking 'Chopsticks.' We're talking Brahms."
For decades, researchers have been trying to replicate the neuromuscular control system of the human body, the path from brain to nerve to muscle that makes it so easy to pick up a coffee cup while talking on the phone and puttering around the kitchen. In 2003, Todd Kuiken, a neurologist at the Rehabilitation Institute of Chicago, took a big step toward that goal when he created an arm that moves in response to nerve impulses. Kuiken transferred shoulder nerves that direct arm function into the chest muscles of Jesse Sullivan, 59, an electrical lineman from Dayton, Tenn., who lost both of his arms after receiving an electric shock on the job in 2001. Sensors glued on Sullivan's chest pick up electrical signals from the nerves and communicate instructions to microchips and motors in the arm. So when Sullivan thinks about picking up a fork or pushing a lawn mower, the arm reacts. In July, a group of scientists announced that a paralyzed man with a "BrainGate" sensor, a silicon chip surgically implanted on the brain's motor cortex and wired to a computer, could move a cursor on the screen by thinking about moving it. He's also able to feel what he touches.
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