An article published in the September 26 issue of the New England Journal of Medicine (NEJM) describes using electromyographic (EMG) signals to improve control of a lower-limb prosthesis through natively innervated and surgically reinnervated residual thigh muscles. The rate of error, including the risk of falls, was reduced from 12.9 percent with a standard robotic leg prosthesis to 1.8 percent with the neuro-controlled powered prosthesis, according to the article. While the researchers expected the leg to operate more smoothly, the magnitude of the benefit was unexpected, they wrote.
Vawter using the neuro-controlled powered prosthesis. Photograph courtesy of RIC.
Levi J. Hargrove, PhD, from the Center for Bionic Medicine, Rehabilitation Institute of Chicago (RIC), Illinois, and colleagues from Northwestern University, Chicago, Illinois, and the University of Washington, Seattle, worked with Zac Vawter, a 32-year old with a transfemoral amputation, to test the effect of EMG signals to improve prosthetic control.
The researchers redirected two severed nerves into Vawter’s hamstring, giving him the ability to use the nerves to produce electricity to then move his knee or ankle. Hargrove et al. found that the reinnervated muscles generated strong EMG signals, and each attempted motion generated distinct signal patterns. The EMG signals were decoded with a pattern-recognition algorithm and combined with data from sensors on the prosthesis to interpret Vawter’s intended movements, providing him with robust and intuitive control while walking, and seamless transitions between level ground, stairs, and ramps. Vawter was also able to reposition the prosthetic leg while he was seated.
The NEJM article is the culmination of continued testing and improvements to prepare the device for clinical application, which may be available within three to five years, Hargrove said in an interview with Bloomberg News.
Vawter began using what researchers from RIC called the first “thought-controlled bionic leg” in November 2012, described in The O&P EDGE article, “RIC Unveils TMR-Controlled Bionic Leg.”
