Walking with a Brain-Powered Bionic Leg

By harnessing the pathways of the brain, researcher Dr. Levi Hargrove is able to outfit Zac Vawter with the world’s first thought-powered bionic leg.

By Edgar Villaruel | UTS Staff Writer | SQ Online (2013-14)

The processing speed of the new iPhone 5S has everyone raving. The phone’s new A7 chip and M7 coprocessor makes surfing the web, arguably, as fast as the blink of an eye. The iPhone’s processor can upload a page in about a second, but this speed cannot compare to the brain’s ability to signal the eye to blink in a mere 400 milliseconds. No man-made technology can trump the processing power of the brain.

Imagine if your beloved iPhone apps stopped working due to a malfunction within its wiring. Even worse, imagine if you lost the ability to walk because your brain did not have the ability to send neurosignals down to your leg. This is what 32-year-old amputee Zac Vawter has to live with every single day.

While fixing an iPhone’s internal wiring can be pricey, it doesn’t compare to the mental, physical, and emotional cost of losing a limb.

Last year, Zac Vawter, climbed one of the tallest skyscrapers (2100 stairs) in the United States, giving fellow amputees a beacon of hope. How did he achieve this? By using brain power.

Firm footing: On Oct. 25, 2012 Zac Vawter, fitted with an experimental "bionic" leg, climbed the 103 flights to the top of Willis Tower in Chicago. Photo by Brian Kersey | AP Photo
Firm footing: On Oct. 25, 2012 Zac Vawter, fitted with an experimental “bionic” leg, climbed the 103 flights to the top of Willis Tower in Chicago. Photo by Brian Kersey | AP Photo

Lower-leg amputees are most commonly treated with implanted mechanical lower-leg prosthetics. However, the mechanical prosthetics available today are passive, like a spring, which means people with these devices have to use their intact limb to pull the prosthetics behind them. Motor-powered lower leg prosthetics may be another option, but are difficult to use because of the exaggerated movements required before changing activities.

Due to these difficult previous treatments, Zac Vawter was courageous enough to try something new: After losing his lower right leg in a motorcycle accident four-and-a-half years ago, Vawter agreed to be the test pilot for the first ever thought-controlled bionic leg.

How Does it Work?

Normally, when a person thinks about moving their lower limb, a signal is fired from their brain, travels through the nerves of their spinal cord, and ultimately arrives at the muscles involved to move that limb. But when an amputation occurs, nerve signals that would have gone to the knee or ankle, for instance, aren’t able to deliver their message to that muscle.

To overcome this problem, researcher Dr. Levi Hargrove from the Rehabilitation Institute of Chicago Center for Bionic Medicine performed a surgery on Vawter to redirect his nerve signals. As a result, signals that would have gone to his lower leg instead go to the healthy hamstring muscle, in the top part of his leg. Electrodes are then conveniently placed on his leg to detect electrical signals from any of the muscle contractions in his hamstring. Finally, a computer program reads the signals to interpret the patient’s control and movement.

Dramatic Improvement and Efficiency

Using the bionic leg, Vawter was able to walk efficiently on ground level, climb up ramps and stairs, and transition between activities without stopping. Most importantly, he was able to use his thoughts to change the position of his lower leg while sitting down, something that he couldn’t do with the mechanical or motorized leg prosthetics.

Vawter’s previous motor-powered prosthetic frequently interpreted his activity incorrectly 12.9 percent of the time. But by using information from the electrodes of the bionic leg, the error rate dropped to only 1.8 percent.

“Reducing this error rate is extremely important, because it can help prevent falls,” Dr. Hargrove said.

Due to the important error decrease, the efficiency of bionic legs trumps both of the two major brands of prosthetics used today.

What’s Next?

This recent development has already made a remarkable difference and impact on the treatment for amputees due to its efficiency and user response.

“It feels how I would normally walk. It’s not special training or buttons or tricks,” Vawter said, about its ease of use. “That’s a big piece of what I think is groundbreaking about this work.”

Although the cost hasn’t been determined, a version could be available to the more than one million Americans with leg amputations within the next three to five years.

The invention of the iPhone is arguably the technology breakthrough of the decade. The breakthrough of the bionic leg, however, can do more than the latest iPhone can claim–it can save lives. In the U.S. alone, about 113,000 lower limb amputees lose the ability to walk every year. Moreover, around 70 percent of these amputees die due to psychological trauma, infection, or accident within five years. This invention can pave the way for ongoing treatment with other patients like Zac Vawter, or victims of cancer, cardiovascular diseases, car accidents, and even veterans who were injured in service.

To see the bionic leg in action, watch coverage on The Verge.