Researchers from Massachusetts Institute of Technology (MIT) announce that they have designed what they reportedly describe is an inexpensive prosthetic knee that can induce normal walking.

In a paper published recently in IEEE Transactions on Neural Systems and Rehabilitation Engineering, lead author Amos Winter, PhD, and the rest of his team note that they have calculated the ideal torque that a prosthetic knee should produce, given the mass of the leg segments, in order to induce able-bodied kinematics, or normal walking, according to a news release from MIT.

Winter is an assistant professor at MIT. His aim, according to the release, is to develop a passive, low-tech prosthetic knee that performs nearly as well as high-end prosthetics, but at a fraction of the cost.

Using the paper’s results, the research team has built a 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 are testing the prototype in India, where about 230,000 above-knee amputees currently live, the release explains.

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

Most amputees in developing countries wear passive prostheses — simple, cheap designs with no moving parts. 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 center of mass steady. In contrast, a stiff, unbending prosthetic knee would cause a person to bob up and down with each step, the release explains.

Winter reasoned that in order to produce a passive prosthetic knee that mimics normal walking, he would have to also mimic the changing forces, or torque profile, during normal walking. He and his team looked through the scientific literature for data on normal walking, and found a complete dataset that represented one person’s gait, including the angle of their joints, the weight of each leg segment, and the ground reaction force — the force between the ground and the foot — during a single step, or gait cycle, the release continues.

The researchers used the measurements to calculate a torque profile — the amount of torque generated by the knee during normal walking. As prostheses are generally one-third to one-half as heavy as human legs and feet, the researchers adjusted the torque profile to apply to lighter leg segments, per the release.

“If you applied healthy levels of torque to a much lighter limb, your kinematics would get all screwed up,” Winter says in the release.

“Robotic limbs are designed to dial that torque back. Our challenge was, how do you tune the torque profile to get able-bodied motion, with a passive prosthetic knee?” he continues

The researchers then looked at whether they could build a prosthetic knee to replicate the adjusted torque profile, using simple mechanical elements. Currently, the group has engineered a simple prototype that includes a spring and two dampers that act as brake pads.

The spring allows the knee to bend just before the foot pushes off the ground. At the same time, the first damper engages to prevent the leg from swinging back. The second damper engages as the leg swings forward, in order to slow it down just before the heel strikes the ground, the release continues.

Winter’s team is now testing the design with volunteers in India, per the release.

“This was a quick and dirty prototype, but so far, we’re seeing good indicators of natural gait,” Winter says in the release.

“I’m not ready to claim victory yet, but [this paper] lays out a road map that is very different than what’s been done before, which will enable us to achieve very high performance at low cost. And that’s what we’re going after,” he notes.

[Source(s): Massachusetts Institute of Technology, Science Daily]