Electric implants in paralyzed legs bring nerves back to life
Michael McClellan pedaled a stationary bike in his Roseville apartment last week, his paralyzed legs thrusting forward in a cycling motion as he wiped the sweat from his brow. He held two remote controllers – one for the television playing the afternoon news and another for the cutting-edge machinery controlling his lower body.
The two-hour cycling regimen is part of the daily schedule for McClellan, a 56-year-old former construction worker who became paralyzed from the hips down after a dirt biking accident in 2009. The technology, called functional electronic stimulation, has helped McClellan and dozens of other people walk, run and pedal again despite their serious injuries. In October, McClellan, a lifelong skier and biker, will continue his sporting pursuits by traveling to Switzerland for the world’s first Cybathlon – an Olympics-style competition for people who use bionic equipment to compete.
Inside McClellan’s legs are 16 silicon electrodes, which surgeons at the U.S. Department of Veterans Affairs implanted near his nerve endings in 2011. When the electrodes are turned on, they transmit electricity to his nerves, making the muscles jump to life in a way that his nervous system no longer can manage.
Researchers have been experimenting with such currents to reactivate damaged nerves since the 1960s. The method has helped paralyzed people stand and even walk, but the newest implant technology is pushing such movement even farther.
The electrodes have always been placed on skin, although they can become displaced by movement and sweat, said Ron Triolo, executive director of the Advanced Platform Technology Center at the Department of Veterans Affairs in Cleveland, who helped develop the system. Implanting electrodes near the muscles or around nerves guarantees that the shock will be consistent and accurate and give the paralyzed person more control over those areas, he said.
“What we’ve been talking about are what we call neuroprostheses,” Triolo said. “Instead of a prosthetic device that replaces a missing limb for an amputee, this is a device that takes the place of a damaged nervous system. ... It’s about triggering the right muscles in the right sequence to generate a pedaling motion in the paralyzed rider. It’s very simple for the user, but very complicated in a way that’s hidden in the technology.”
After the bursting of McLellan’s T11 vertebrae confined him to a wheelchair, he researched new technologies that might help him regain mobility. That included physical therapy as well as visiting the Berkeley Robotics and Human Engineering Laboratory to try eLegs, a powered exoskeleton that helps people walk, before getting connected to Triolo.
Shortly after meeting the team in Cleveland, McClellan underwent implantation surgery to embed 16 electrodes in his quads, hamstrings and gluteus maximus muscles. The electrodes are all controlled by a central stimulator, which is sewn into McClellan’s abdomen. With the flick of a switch, he can trigger a nerve group and watch his legs come to life. McClellan said the implants haven’t felt strange or robotic on him and he has been able to maintain much of his athleticism after the injury.
Instead of a prosthetic device that replaces a missing limb for an amputee, this is a device that takes the place of a damaged nervous system.
Ron Triolo, executive director of the Advanced Platform Technology Center at the Department of Veterans Affairs in Cleveland
“When you first do it, it makes you kind of giddy,” he said. “It’s exciting, and thrilling.”
At the upcoming Cybathlon, McClellan will be one of two Northern California men representing Team Cleveland in the functional electronic stimulation bike race for paralyzed people who have spinal cord injuries but can ride a bicycle using devices such as the one Triolo and his colleagues designed.
Mark Muhn, 59, of Morgan Hill, has also been training for the Cybathlon, although only one of the two men will compete in the race. He became paralyzed in a skiing accident in 2008.
The two men have been neck and neck with their race times all summer, with both completing the 750-meter course in about 2 1/2 minutes.
“It’s a long way to go to being perfect,” Muhn said of his bike. “But I’m taking what I can get, and I’m happy to have it. I got in at a pretty good time. Whatever we learn with me and Michael will help somebody 20 years from now when the technology is much better. This will really push the technology for the future.”
There are limitations to the innovation – muscles can take only so much stimulation before they fatigue, Triolo said. Part of the cycling team’s challenge will be finding the right combination of nerve firings to pedal the bikes, but not exhaust the riders.
Triolo and the research team have modified competition bikes that improve communication between the pedals and the rider’s electrode implants. When they first started experimenting by duct taping McClellan’s paralyzed legs to the pedals, it was difficult to get the firing muscles to stay in sync with the equipment.
“The bikes had to be adapted so that the stimulator actually knows where the pedals are at any point in time,” Triolo said. “We fit an encoder that senses the angle of the crank, and the stimulation changes depending on what that angle is. The muscles you need to push the crank when it’s at 90 degrees is different than what it is at 180 degrees.”
Triolo hopes to expand the use of functional electronic stimulation technology to stroke survivors or people with multiple sclerosis.
McClellan said the technology has been a life changer. He lives alone and cares for himself and his dog without assistance. While he can’t use the stimulator to walk around regularly, it helps him to stand up if he braces his weight on a countertop or a wall. On one occasion he used it to walk down an airplane aisle while holding onto the plane’s seat backs because he had to catch a connection and couldn’t wait for a wheelchair to arrive.
Muhn has also used his implants to power through his daily routine.
“I do walk a little bit just because I can,” he said. “I can walk around the kitchen, walk around the living room, just to get up and move. I stand for an hour at a time now. It’s incredible. It’s really incredible.”