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exoskeletons & prosthetics
Tue June 25, 2013
Horse-inspired mechanical legs helping stroke patients walk again
A research idea that was supposed to give people super-powered legs is instead helping stroke patients and other people who can’t walk.
It’s a new medical device, using a combination of springs, cables, and Velcro. The inventors in Seattle are hoping to transform the possibility of recovery for thousands of people.
The idea started with a horse.
The reason horses can run so much faster and more efficiently than humans is not just their size. It’s also because of the tendons in their legs.
“They have these very long tendons that stretch from the hip down to the ankle, as opposed to humans who have really short tendons that just stretch across single joints.” said Brian Glaister, an engineer and co-founder of a tiny Seattle startup called Cadence Biomedical in Wallingford.
The insight about tendons—and a gee-whiz idea to make us all run like horses—came originally from a scientist in Cleveland, A.J. van den Bogert.
“[He] had an idea of, well, why don’t we put a long spring on a human and see if we can make them as efficient as a horse. They had the idea, but didn’t know how to build it or bring it to market,” said Glaister.
What happens if you put a super-tendon on a human
Van den Bogert contacted Glaister and his engineering buddy Jason Schoen, who were inventing new devices as researchers at the Seattle Veterans Administration Hospital.
They started working on a model. Pretty soon, they saw, there’s no way it could work. If you tried to put a super-strong tendon on a human, you’d crush the bones in their legs, said Glaister.
So, forget super-human strength.
On the other hand, the idea of a cable that extends from the hip to the ankle – now, that might help someone who can’t lift their leg, they realized. For example, many stroke victims have trouble with the muscles that lift your leg upward and keep your toe from dangling down.
“The hip flexor muscle is on front of hip, and it’s there to help you lift your leg off the ground,” said Glaister. “If you can’t lift your leg off the ground, you drag it behind you or you try to swing it around, and it’s terribly inefficient. So, many people just opt for a wheelchair.”
Case study: He’s able to walk the mall
Carl Simmons had a stroke five years ago, and he recovered pretty well – except for his right leg. The only technology available was a stiff, plastic boot.
“It was supposed to help me straighten my foot out. It didn’t help me with my knee or anything like that,” says Simmons, 76, of Lynnwood.
He could barely walk, using a cane. As a former runner, he was frustrated to limp along and then sit on a bench at the mall, while his wife shopped.
A specialist in Seattle, at the Center for Prosthetics Orthotics, put him in the device that Brian and Jason had invented, inspired by the horse. They call it the Kickstart Walking System.
Simmons sits in a chair to put it on, attaching black Velcro straps around his thigh and calf, and then buckling a belt around his waist. At first glance, the device look like a knee brace you might wear after surgery.
What’s unusual—and relates back to the horse—is the thick cable that runs from the belt, down the side of his leg, and into a customized New Balance shoe on his foot.
“Now I'm putting some tension into the cable,” says Simmons after standing up in the brace. He counts to ten as he tightened an adjustable gear at the hip, sort of like reeling in a fishing line.
In the middle of the cable is a spring. That allows the cable to stretch and then snap back as he swings his leg.
“It assists, no doubt about it,” he says.
Now he’s retraining himself how to take normal length strides by lifting the knee. He’s re-learning how to walk, and after just a couple weeks, he can move pretty well down a practice track in the examining room.
The progress feels dramatic to his wife, Peg Simmons. She says a few weeks ago, they couldn’t really walk together.
“I used to have to go really, really slow,” she said. “We had a situation just this past week where he was way ahead of me in the mall.”
How it works
The secret to making this whole thing work is an ordinary coiled metal spring that looks like the kind you’d find in a hardware store.
Schoen demonstrates how it works.
“As I take a step forward with my unimpaired side, I'm adding essentially more length into the spring,” he said, so that the spring stretches when you step forward, and then recoils.
“The spring recoils in such a way that it’s directed toward my hip, to help pick my leg up off the ground.”
For an unimpaired person, the pull of the spring makes your leg feel like it wants to leap forward. But it’s more like a gentle push—not nearly enough leap to help you dunk a basketball.
The Kickstart currently costs between $5,000 and $6,000 for Medicare patients; some private insurers may cover more.
It fits into a growing niche of new medical devices for people trying to recover from strokes or injuries. They're changing the idea of rehabilitation. The goal in physical therapy nowadays is to get the damaged limb moving again, by any means necessary. Over time, that can teach the brain to map a new pathway to the damaged leg or arm.
Mechanical limbs re-wire the brain
“If I'm walking, or I'm able to get to the store and I'm able go shopping, or I'm able to drive my car because I have a dynamic orthosis on that allows me to perform these activities, then I'm driving changes in my brain,” said Nancy Byl, a professor of physical therapy at the University of California, San Francisco Medical School, who has researched and tested dozens of prosthetic devices, including the Kickstart.
Those brain changes require thousands of repetitions, and it’s hard to get that much time with a physical therapist. A mechanical device lets you practice all day.
Many of the new devices are high-tech, involving computer chips and sensors that measure muscles and position. The most elaborate provide a mechanical skeleton, such as the Ekso, which can allow a paralyzed person to stand up. Those run nearly $100,000 and still await approval from the Food and Drug Administration for home use.
On the simpler end of the spectrum, the Walkaide straps onto your calf and electrically stimulates a muscle that’s not working.
The Kickstart has its niche by being low-tech, and inspired by a horse.
Carl Simmons, 76, of Lynnwood, who had a stroke in 2008, tests how much faster he can walk with Kickstart, with his orthotist Julie Schaar at the Center for Prostetics Orthotics in Seattle, WA.