A month after one of his patients made headlines as “the world’s first bionic woman,” Todd Kuiken-physician, prosthetics pioneer and Oak Park resident-headed to the Oak Park Public Library (Oct. 10) to give a lesson in rebuilding the human body.
Prosthetics, he told the audience of roughly 50 listeners (including his wife and two young sons), has long lagged behind the rest of medical science. Having lost all or part of an arm, most amputees must still rely on cumbersome-albeit reliable and inexpensive-body-powered replacements. Opening an artificial hand, for instance, means spreading the shoulders. Operating an artificial elbow requires substantial exertion and a complex harness.
Meanwhile, motorized prostheses, that respond to electric signals from contracting muscles, lose their effectiveness in amputations above the elbow. Leg amputees, who constitute 90 percent of people with missing limbs, wear “passive devices,” Kuiken said.
“You bring them along for the ride and then stand on them.”
For 20 years, he has worked to develop better, more organic and graceful prostheses. “Prosthetic technology is so primitive it amazes us,” he said. “We know we can do better.”
Five years ago, Kuiken, director of amputee services-and of the Neural Engineering Center for Artificial Limbs-at the Rehabilitation Institute of Chicago (RIC) did just that. Experimenting with a procedure Kuiken calls “targeted reinnervation,” his team of surgeons, prosthetists and biomedical engineers fitted Jesse Sullivan, a 54-year-old high-power lineman who’d lost both arms at the shoulder when he touched the wrong wire, with two new ones he could control by thought alone. “When you have an amputation, you lose the bone and the muscle, the skeleton and motors of the arm,” Kuiken said. “But the control line is the nerve, and it’s still there.” His RIC medical team grafted Sullivan’s shoulder nerves, which used to go to his arms, to spare pectoral muscle and allowed them to grow there. Four nerves, each governing a different motion, were routed to four different sites on Sullivan’s chest.
“So when he thinks, ‘Close hand,’ for instance, a little piece of the chest muscle will contract,” Kuiken said.
Electrodes on Sullivan’s skin pick up that signal and command his computerized artificial hand to close. “You can control more things at the same time-not just the hand, but the wrist and elbow, too-and in a natural way,” Kuiken said. “It’s easier and more intuitive. The muscles actually act as a biological amplifier to amplify that signal 1,000 times.”
On a screen behind him, Kuiken projected videos of Sullivan picking up and moving small objects, first with an old-fashioned artificial arm and then wearing his new nerve-controlled prosthesis. The difference in speed and nimbleness was striking.
“After two months of training, he was 2 1/2 times as fast” with the computerized arm, Kuiken said, and much more fluid. A little less than a year later, Sullivan can move his computerized arm 3 1/2 times faster. “He can throw a ball now, because he’s able to use his hand and his elbow at the same time.”
Since their experiment with Sullivan, Kuiken’s team has performed targeted reinnervation on five other patients. Most recent was “bionic woman” Claudia Mitchell, a 26-year-old former Marine whose left arm was severed at the shoulder during a 2004 motorcycle crash on an Arkansas highway. A more advanced version of Sullivan’s $4 million arms, Mitchell’s 10-pound artificial limb houses six-rather than three-motors.
Her surgery had to be updated, too: “The main challenge,” Kuiken said, “was that as a young lady, she has breasts.” To get Sullivan’s electrodes as close as possible to the nerves’ electrical signal, surgeons had removed the fat between the skin and pectoral muscle; with Mitchell, that wasn’t possible. Kuiken’s team ended up transferring her nerves to muscle high on her chest and off to the side. The surgery was a surprising success.
“There’s actually more fidelity, in that Claudia can feel individual fingers in a way Jesse can’t,” Kuiken said. “So we have much more to learn in controlling this phenomenon.”
The team has been lucky at least once before-after his surgery, Sullivan discovered an unexpected ability to move his thumbs individually. “Luck’s handy, but we’d like to do it on purpose,” Kuiken said. “We think we can do the surgery a lot better.”
He’s got other projects percolating, too. Maybe it’s possible, he said, to surgically divide each nerve and extract even more information about moving fingers and thumbs and wrists. Maybe there’s a way to adapt nerve innervation to leg amputees who make up, after all, the bulk of prosthesis patients. Certainly the artificial arms themselves can be made sturdier, nimbler, lighter. Sweat sometimes interferes with the electrodes, a problem for people like Sullivan, who likes to mow the lawn with his bionic arms.
Spurred by the thousands of veterans returning from Iraq and Afganistan with missing limbs, the Army is investing heavily, Kuiken said, in the effort to build better prostheses. “I’m not worried about early retirement,” he said. “We have lots of things to do.”
During a Q&A that followed his talk, Kuiken answered most questions with some version of “maybe.” Could the surgery work on children who haven’t fully developed? “I don’t know,” Kuiken said. “It depends on how well their nerves are grown, and that’s not well known.” Would he consider doing the surgery on amputees who are also cognitively impaired (as many war veterans are)? Not right now, Kuiken said.
“We may get to the point where doing something like targeted reinnervation would actually enable a person to use a prosthesis they couldn’t otherwise use, but that’s a risky area. I wouldn’t try that until I have done this on lots and lots of people and have a lot of experience.”
One audience member wanted to know about the potential for patients to have spatial awareness of their artificial limbs? “Proprioception”-the ability to sense location, position and orientation of a body part-“is a really complex thing,” Kuiken said, especially given that the hand alone has 30,000 sensation nerves. Somehow, Mitchell gained a touch of proprioception in one spot on her finger.
“Why did that happen? I don’t know,” Kuiken said. “How to make that happen in useful ways? I don’t know. I’d like to find out.”