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This New Bionic Leg Makes Stairs and Slopes No Obstacle

"You don't have to think about walking with this leg."
June 9, 2015, 3:00pm
Image: Sheila Burt/Rehabilitation Institute of Chicago

Sculptor Terry Karpowicz was 27 when a motor accident resulted in the loss of his right leg. For years since, Karpowicz has been using computerised C-Leg prosthetic. But now, he's hoping that a new bionic will give him a wider range of motion than he's ever had before.

Karpowicz is one of seven patients who trialled the prototype leg device at a research laboratory at the Rehabilitation Institute of Chicago. In a study published today in The Journal of the American Medical Association, researchers at the institute focused on finding out how their bionic leg device could allow patients to transition smoothly between different movements.


"If you're walking and want to climb up some stairs, you have to stop at the bottom and change the configuration of your prosthesis. We've been working on using neural signals decoded through your muscles, which automatically allow a user to transition through a number of different activities," said Dr. Levi Hargrove, lead study author and director of the Neural Engineering Lab at the Rehabilitation Institute of Chicago, in an interview.

The researchers recorded electromyographic signals (EMG) using electrodes placed over each patient's nine residual limb muscles, as well as data from 13 mechanical sensors embedded on the prosthetic, while patients did everything from level-ground walking to climbing up stairs and slopes. A pattern recognition algorithm combined the EMG and mechanical signals, and was used to anticipate how the patient intended to move.

"With my C-Leg I have to make sure that I'm in the right position so that I don't strain myself. With [the bionic leg] you can climb ladders and go from kneeling to standing," Karpowicz told me on the phone. [Edit: These activities aren't currently possible with the leg but could be in the future].

Terry Karpowicz with his prosthetic leg at the Rehabilitation Institute of Chicago. Image: Ann Simon/Rehabilitation Institute of Chicago

Bionic leg prosthetics have been slowly inching their way towards the market. In May 2015, Icelandic orthopaedics company Ossur announced a "mind-controlled" bionic leg, which it aims to have on the market in three to five years. Massachusetts-based, startup BiOM, has also been working on lower-leg prosthetics since 2007. But there are still some challenges. Making an above-knee powered prosthetic is harder than a below-knee one, as researchers have to replicate the natural movements of two joints: the knee and the ankle.

"Developing a control system for legs is a little more difficult because it has to be accurate, reliable and robust. If you're controlling a bionic arm and the fingers aren't moving exactly as you'd like them to, the user may not notice the misbehaviour, or it might not bother them," said Hargrove. "However, if you're walking and the device isn't in the configuration that you want it to be in, you'll stumble and that's a potential safety risk."

The prosthetic is battery powered, lasts for around 12 hours, and can be recharged overnight. It currently weighs in at roughly ten to 20 pounds, or about the same weight as a an average male leg. Karpowicz told me that the weight took a little getting used to when he initially tried out the leg, but said that as they were still at the early stages of the trial, he couldn't complain.

"It's light years ahead of my current prosthetic leg," Karpowicz said. "You don't have to think about walking with this leg. Once you start thinking about where you're going, [the bionic leg] anticipates what you want to do."

The study published today is only based on in-lab research, But the researchers are currently carrying out a four-year US Army sponsored home trial where they are letting 15 patients try out the devices at home. The trial is aimed at turning the prosthetic into a commercial product geared towards people who have amputations resulting from military or motor vehicle accidents, cancer or diabetes.

Hargrove estimated that the initial cost of the bionic leg would be around $40,000, which he said was similar to the cost of a powered prosthetic knee or ankle. He hopes, however, to keep costs to a minimum by leveraging improvements in microprocessors in the mobile phone industry, or using 3D printing where appropriate in the future.