Wounded Veteran Among Those Benefiting From 'Smart' Prosthetic Ankle

By Rob Hawley
WCBS 880

NEW YORK (CBSNewYork) -- Ten years ago, David Bronson's life changed forever.

Like so many American soldiers serving in Iraq, the now-retired Army sergeant was the victim of an improvised explosive device. His lower left leg had to be amputated, and he started to relearn how to live and walk with a prosthetic leg.

A lot of his thinking began to revolve around things that most people take for granted -- like how to walk on different terrain, such as grass or sand, or how to handle sidewalks that might not be perfectly flat. And Bronson says he had to think a lot about how far he could go.

"If you're going to be walking through a mall, how long you can actually walk, how long your stamina will last," he says.

He says he had to think a lot about things like that with what he calls the "dumb legs." But now he has a smart leg.

The BiOM Ankle, made by Bionx Medical Technologies in Bedford, Massachusetts, is a very smart ankle. CEO and President Dr. Charles Carignan says it has "15 different sensors that are measuring different parameters with every step that the person is taking, and that data is being processed by three different onboard computers." In a matter of milliseconds, those computers figure out how fast the patient is walking and the type of terrain. Then they can calculate just how much power the onboard motors should deliver.

All of the features of the BiOM ankle -- the flexibility in the ankle, the motors and carbon fiber spring that help replace the calf muscle that has been lost, and the computers that handle all the calculations -- set it apart from other prosthetics. Bronson says when he first got his, he was surprised by how heavy it was. But when the switch was flipped for the first time, he says he didn't even feel the weight anymore.

"It's crazy how much push-off it has and how natural it feels," he says.

And he's done just about everything with this ankle.

"I wear it every day," Bronson says. "I do everything from playing with my kids in the yard to hunting, golfing, snowmobiling."

One place where it really helps is walking down a hill. Carignan says he tells people to think about trying to walk down a hill wearing a ski boot. Since your ankle can't flex, you suddenly find yourself tipping forward. That's the way most people wearing prosthetics feel every time they try to go down a hill. But Bronson says, with the BiOM Ankle, since it flexes, "it will lay the foot all the way flat, instead of just being able to dig the heel in, so it's a much more natural gait."

All of this, of course, requires power, and the BiOM Ankle gets its power from rechargeable batteries that look a lot like the battery you plug into a cordless drill. One battery will typically give a patient about 3.5 hours of walking time. Bronson says he often carries a spare battery around. When the power is off, he says it's like a traditional prosthetic, and he can definitely feel the weight. Carignan says Bionx is looking at ways to make the batteries both more compact and last longer.

Looking down the road five to 10 years, Carignan says his company wants to tie sensors into the existing muscles and nerves of the patient so they could have more active control over how the ankle works.

"Right now, we determine what you intend to do based on how you strike the ground on your heel strike or just with your toe if you're going upstairs," he says. "What we'd like to do is to be able to have your body start to signal to the ankle what your intention is."

For his part, Bronson is looking forward to the next evolution of the BiOM Ankle. He's been working closely with the Bionx team on improvements that include everything from more movement in the ankle to being able to wear it into water.

He admits that soon after he was injured, he didn't know if he'd be able to do the things he loves, like ride a motorcycle or play hockey. But now he says he does just about everything he can think of to test his limits and the limits of the BiOM Ankle.

"I pushed through and was able to prove to myself that I can still do everything and endure it," Bronson says. "And there's nothing that really holds me back."