This smart prosthetic ankle adjusts to rough terrain

Prosthetic limbs are getting better and more personalized, but useful as they are, they’re still a far cry from the real thing. This new prosthetic ankle is a little closer than others, though: it moves on its own, adapting to its user’s gait and the surface on which it lands.

Your ankle does a lot of work when you walk: lifting your toe out of the way so you don’t scuff it on the ground, controlling the tilt of your foot to minimize the shock when it lands or as you adjust your weight, all while conforming to bumps and other irregularities it encounters. Few prostheses attempt to replicate these motions, meaning all that work is done in a more basic way, like the bending of a spring or compression of padding.

But this prototype ankle from Michael Goldfarb, a mechanical engineering professor at Vanderbilt, goes much further than passive shock absorption. Inside the joint are a motor and actuator, controlled by a chip that senses and classifies motion and determines how each step should look.

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“This device first and foremost adapts to what’s around it,” Goldfarb said in a video documenting the prosthesis.

“You can walk up slopes, down slopes, up stairs and down stairs, and the device figures out what you’re doing and functions the way it should,” he added in a news release from the university.

When it senses that the foot has lifted up for a step, it can lift the toe up to keep it clear, also exposing the heel so that when the limb comes down, it can roll into the next step. And by reading the pressure both from above (indicating how the person is using that foot) and below (indicating the slope and irregularities of the surface) it can make that step feel much more like a natural one.

One veteran of many prostheses, Mike Sasser, tested the device and had good things to say: “I’ve tried hydraulic ankles that had no sort of microprocessors, and they’ve been clunky, heavy and unforgiving for an active person. This isn’t that.”

Right now the device is still very lab-bound, and it runs on wired power — not exactly convenient if someone wants to go for a walk. But if the joint works as designed, as it certainly seems to, then powering it is a secondary issue. The plan is to commercialize the prosthesis in the next couple of years once all that is figured out. You can learn a bit more about Goldfarb’s research at the Center for Intelligent Mechatronics.