RIC Announces Preliminary Results Demonstrating Neural Control in Lower-Limb Amputees

The Rehabilitation Institute of Chicago (RIC), Illinois, has announced preliminary results demonstrating real-time neural control of knee and ankle motions for lower-limb amputees. Results from the early-stage research, authored by Levi Hargrove, PhD, research scientist at RIC's Center for Bionic Medicine, were published in the April 20 issue of the Journal of the American Medical Association (JAMA).

"Our preliminary results demonstrate successful neural control of both the ankle and knee joints and represent a significant step in our efforts to develop a neural-controlled prosthetic leg for the millions of people living with lower-limb loss worldwide," Hargrove said. "There is much work to be done, but what we have found is a meaningful sign for a future of more advanced prosthetic control and artificial limbs for lower-limb amputees."

With lower-limb amputees forming a large portion of the amputee population, there is a significant unmet need for the development of a neurally controlled prosthetic leg. However, RIC notes that there are challenges in transitioning the current bionic technology for upper limbs to lower limbs due to some inconsistencies in recording neural, or electromyographic (EMG), signals. While research to-date has provided some insight into overcoming these challenges, additional studies are needed to evaluate and develop a novel lower-limb neural interface.

Hargrove's research investigates real-time neural control in four lower-limb amputees and four non-amputee control participants, measuring the EMG signals in nine lower-limb muscle sites during lower-limb movement. Through real-time tests, all participants were instructed to move a virtual lower limb through a variety of motion patterns on a computer screen. Metrics were based on accuracy of movement, the time it took to complete the motion, and the percentage of successfully completed motions.

Results from the trial showed all participants were able to control their knee and ankle from neural information measured in the thigh. The average motion completion rate for knee and ankle movements (knee flexion/extension and ankle dorsiflexion/plantarflexion) was 97.2 percent for amputee patients and 95.1 percent for control participants. The average motion completion times for knee and ankle movements were 2.53 seconds for amputee patients and 1.94 seconds for control participants. The average accuracy of movement rates were 91 percent for amputee patients and 89 percent for control participants.

Findings from Hargrove's study complement RIC's work in providing upper-limb amputees with neural control of prostheses, through its targeted muscle reinnervation (TMR) procedure and development of a neutrally controlled bionic arm. TMR, pioneered in 2002 by Todd Kuiken, MD, PhD, director of RIC's Center for Bionic Medicine and director of Amputee Services at RIC, is a surgical procedure that reroutes brain signals from nerves severed during amputation to intact muscles, allowing patients to control their robotic prosthetic devices by merely thinking about the action they want to perform. According to RIC, the procedure has benefitted more than 50 upper-limb amputees worldwide.

"These findings in JAMA also showed that real-time ankle control was attainable by only using EMG signals from the thigh muscles, leading me and my colleagues to believe that TMR surgery may not be necessary for amputees to regain control of knee and ankle movements with prostheses," Hargrove said. "We look forward to applying these findings to our continued research investigating neural control in lower-limb amputees and the future development of advanced physical knee and ankle prostheses."