Zac Vawter’s bionic leg lets him walk up stairs with ease. That’s because it senses his brain’s instructions and moves accordingly, something that no other prosthetic leg can do.
The leg is the first of its kind to respond accurately to its user’s thoughts, according to a report published Sept. 26 in the New England Journal Of Medicine.
Vawter, now 32, was in a motorcycle accident in 2009. Doctors had to amputate his leg just above the knee.
He had heard about mind-controlled prosthetics, which had previously only been used with robotic arms. Legs are more problematic, because when they fail you are more likely to get badly injured, for instance, by falling down the stairs.
He asked about these new technologies and eventually became the “test-pilot” for a bionic leg created by Todd Kuiken’s team at the Rehabilitation Institute of Chicago. The project was partially funded by an $US8 million grant from the U.S. Army.
The bionic leg uses electrodes and a microprocessor to read Vawter’s intentions via muscle contractions in his thigh.
Normally, the brain sends electrical signals through the spinal cord to instruct muscles to move. For a leg amputee, those signals still occur, but there is no longer anywhere for that signal to go. Because of this the nerves near the amputation site tend to die off, leaving a dead circuit.
To avoid this, during the amputation, doctors rewired Vawter’s nerves so they could control muscle contractions in his thigh. This kept the nerves alive.
Within a few months of the surgery, Vawter’s nerves began carrying electrical impulses to the muscles of his thigh. When Vawter thought about curling his toes or moving his leg, his thigh muscle contracted in distinct ways.
Vawter spent hours with his rewired thigh hooked up to electrodes, while the team recorded the electrical signals produced when he thought about making certain movements with his leg. The team then used pattern recognition software to digitize and catalogue the movements.
The bionic leg was programmed to understand the signals and respond with the appropriate movement or action.
“When the patient thinks about pushing his toes into the ground, called plantar flexing or lifting, and pointing his foot up, called dorsal flexing — essentially moving his ankle — instead of causing muscle that is below his knee to contract, those nerve signals have been redirected and his hamstring contracts,” Levi Hargrove, the lead researcher on the team, told Medscape.
They’ve been working on the prosthetic and the software that goes with it for a long time, but now, it is nearly flawless — it responds correctly 98% of the time.
It has been so successful that Vawter climbed to the top of the 103-story Willis Tower in Chicago last year, according to The Chicago Tribune. Because the bionic leg is still in development, Vawter does not get to use it every day.
Even when he does wear it, the bionic leg is not yet an equivalent replacement for his real leg. Before his accident Vawter could dunk a basketball. The prosthetic isn’t good enough to let him do that yet.
“It’s in between the leg I wear every day and prior to amputation,” Vawter told Bloomberg News. “It’s a dramatic improvement over my current prosthetic, but there is still a long way to go.”
And the team is still going — they are making it lighter and quieter, and improving battery life. Right now, the leg is good for 5,000 steps or about 2.5 miles. The army wants it to be able to perform twice that.
The technology could be on the market in three to five years, according to Hargrove. But it only works with people who have had their nerves attached to muscles in their thighs.
See the prosthetic in action:
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