Researchers at Massachusetts Institute of Technology (MIT) have designed a prosthetic knee that mimics normal walking motion — and after successful initial results its prototype will be tested in India.

The team has built the prototype of a prosthetic knee that generates a torque profile similar to that of able-bodied knees, using only simple mechanical elements like springs and dampers.

They prototype will be tested in India, where about 230,000 above-knee amputees currently live.

The invention has the potential to revolutionise the prosthetic limb industry as good prosthetics cost several thousand dollars.

For instance, a top-of-the-line prosthetic — that incorporates microprocessors which work with on-board gyroscopes, accelerometers, and hydraulics to enable a person walk with a normal gait — can cost around $50,000.

Amos Winter, an assistant professor of mechanical engineering at MIT, said his team has developed a passive, low-tech prosthetic knee that performs nearly as well as high-end prosthetics, at a fraction of the cost.

“If we can make a knee that delivers similar performance to a $50,000 knee for a few hundred dollars, that’s a game-changer,” said Winter.

“In places like India, there’s still stigma associated with this disability. They may be less likely to get a job or get married. People want to be incognito if they can,” he added.

Most amputees in developing countries wear passive prostheses — simple, cheap designs with no moving parts.

“When you see people walk in them, they have a pretty distinctive limp,” Winter said.

In part, that’s because passive prostheses do not adjust the amount of torque exerted as a person walks. For instance, in normal walking, the knee flexes slightly, just before the foot pushes off the ground — a shift in torque that keeps a person’s centre of mass steady.

In contrast, a stiff, unbending prosthetic knee would cause a person to bob up and down with each step.

The researchers used the measurements to calculate a torque profile — the amount of torque generated by the knee during normal walking.

“Our challenge was, how you tune the torque profile to get able-bodied motion, with a passive prosthetic knee,” winter explained.

“This was a quick prototype, but so far, we are seeing good indicators of natural gait,” Winter said.

The finding was reported in IEEE Transactions on Neural Systems and Rehabilitation Engineering.

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