Cheaper, high-performing prosthetic knee being tested in India

The most advanced prostheses incorporate microprocessors that work with onboard gyroscopes, accelerometers, and hydraulics to enable a person to walk with a normal gait. Such top-of-the-line prosthetics can cost more than $50,000.

Amos Winter, an assistant professor of mechanical engineering at Massachusetts Institute of Technology, is developing a low-tech prosthetic knee that performs nearly as well as high-end prosthetics, at a fraction of the cost.

Winter and his colleagues 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.

In a paper published in IEEE Transactions on Neural Systems and Rehabilitation Engineering, the team reported that it 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.

The prototype is being tested in India, where about 230,000 above-knee amputees currently live, researchers said.

“In places like India, there’s still stigma associated with this disability. They may be less likely to get a job or get married,” Winter said.

The paper’s co-authors include graduate student Murthy Arlekatti and Yashraj Narang, a PhD student at Harvard University.

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 is 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.