After losing his lower right leg in a motorcycle accident four-and-a-half years ago, 32-year-old Zac Vawter has been fitted with an artificial limb that uses neurosignals from his upper leg muscles to control the prosthetic knee and ankle. The motorized limb is the first thought-controlled bionic leg, scientists at the Rehabilitation Institute of Chicago reported Wednesday in The New England Journal of Medicine.
When Vawter thinks he wants to move his leg, the brain signal travels down his spinal cord and through peripheral nerves and is picked up by electrodes in the bionic leg. Unlike robotic models currently on the market, the prosthesis allows a normal, smooth gait no matter the incline.
“It makes a phenomenal difference,” says Vawter, a software engineer from Yelm, Wash., whose right leg was amputated through the knee in 2009 after he crashed his motorcycle. Aware of the institute’s work on bionic arms, Vawter and his surgeon contacted Hargrove and the team developing the pioneering prosthesis. For nearly three years ending in October, 2012, Vawter would travel to the institute periodically.
Vawter would remove his mechanical leg, slip into the bionic one, and run through a set of experiments the scientists devised, suggesting improvements and providing feedback on what was working and what was not.
Two electrodes pick up signals from the hamstring muscle, where the nerves that had run through Vawter’s lower leg were redirected during the amputation. “So when Zac is thinking about moving his ankle, his hamstring contracts,” says Hargrove.
More electrodes pick up signals from other muscles in the residual limb. The complex pattern recognition software contained in the on-board computer interprets these electrical signals from the upper leg as well as mechanical signals from the bionic leg and “figures out what Zac is trying to do,” says Hargrove.
The U.S. Army’s Telemedicine and Advanced Technology Research Center funded the Chicago study with an $8 million grant to add neural information to the control systems of advanced robotic leg prostheses. Devising a thought-controlled bionic leg has been more challenging than a thought-controlled bionic arm, says Hargrove.
That’s because the motors must be powerful enough to provide the energy to allow someone to stand and push along — and they must be small. Also, the computer control system must be safe.
“If there is a mistake or error that could cause someone to fall, that could be potentially catastrophic, and we want to avoid that at all costs,” says Hargrove.
source: NBC News Channel