Building a Better Limb
Veterans are inspiring a big push to create thought-controlled prosthetics
James Stuck thinks his newest right foot is "pretty cool"; it can sense when he's headed downstairs or climbing up a slope and angle itself accordingly. A great choice for hiking. But when the 22-year-old Army specialist from New Kensington, Pa., wants to play soccer, this foot's "not quick enough to keep up." For that, he pulls on one of the five others in his arsenal. They're not "smart" like his new foot, but each has a strength, be it springiness or lightness. He chooses depending on what he plans to do: run, snowboard, play basketball, climb a tree.
Stuck lost his right leg below the knee last December, when his armored humvee hit an explosive device near Kirkuk, Iraq. At that moment, he joined a group of wounded soldiers unique in the history of battlefield medicine. Improved body armor and speedy emergency care have reduced the death rate among Americans wounded in Afghanistan and Iraq to a historic low, but the amputation rate is up by 100 percent. The result: an unprecedented wave of research on prosthetics, aimed at bringing a primitive technology into the 21st century.
A market. Until Iraq, companies had little incentive to develop high-performance prosthetics, since most of the country's approximately 1 million people missing a limb are older and often frail victims of diabetes or vascular disease. But Stuck and his comrades are young, athletic, and impatient--and have no intention of quietly retiring on disability. "Our soldiers have really inspired the research community to apply the science to help," says Lt. Col. Paul Pasquina, medical director of the amputee program at Walter Reed Army Medical Center in Washington, D.C. Much of the new research is being funded by the Defense Department--including a $48.5 million program that aims to build a "thought controlled" arm by 2009 that's as strong and agile as Luke Skywalker's in Star Wars.
Stuck is doing his bit to advance prosthetic science. In late June, he became one of two patients at Walter Reed to test the new Proprio foot, a 2.5-pound, motor-powered appendage with sensors that detect terrain changes and "artificial intelligence" that realizes the person is going upstairs, say, and bends the ankle accordingly. Other prosthetics have a fixed ankle, making stair-climbing "like walking uphill in a rigid cast," says Ian Fothergill, prosthetist at Ossur, which created the foot. The Proprio follows the hugely popular Otto Bock C-Leg, featured in Doonesbury, which was the first device to use microprocessors to control the leg's swing, thus making walking less tiring. Last year, Ossur introduced the Rheo Knee, a prosthetic that uses artificial intelligence to remember and adapt to the user's tendencies. And the company is about to unveil the motorized Power Knee, which bends and lifts as if controlled by a well-toned quad muscle. These computer-driven prostheses react too slowly for running but complement innovations such as the Flex-Foot, a spatula-shaped piece of carbon fiber that's light and springy and has some Walter Reed patients running within months of being injured.
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.
Next steps. A direct connection into the nervous system like the BrainGate should provide clearer, more varied signals than sensors glued on skin, and thus more motion control and sense of touch. But plugging wires into humans isn't as simple as plugging an electric toothbrush into the bathroom socket. Surgery always involves risks, and the implantable sensors that have been tried so far sometimes shift and damage nerves or cause infection. They also lose their ability to pick up signals over time, for reasons still unknown. Scientists now building the DARPA arms were already experimenting with different sensor designs that might solve these problems. They include BIONs, rice-size glass-encased transmitters that could be injected into a muscle to pick up electrical signals from nerves, and electrode arrays that would be implanted at the ends of peripheral nerves, which run from the spinal cord through the body, sending signals from and to the brain. "The challenge is going to be how long those interfaces will last and the risk they pose to the patient," says Stuart Harshbarger, project manager at APL. He hopes to be testing a thought-driven arm in humans in early 2008.
Kuiken, who is involved in several aspects of the DARPA projects, likens the infusion of money to "taking what I'm doing and putting it on rocket fuel." He is now studying cadavers to see if he can split nerves and create new branches, then apply the techniques to orchestrate a wider variety of motion in an artificial arm with living nerves in patients.
"I don't think anybody really knows how far we're going to get in two years," says Dean Kamen, founder of DEKA. "But I'm confident we're going to get to something that's going to put a smile on the face of a whole lot of veterans."
This story appears in the July 31, 2006 print edition of U.S. News & World Report.