Robotic leg prostheses tend to be simpler than artificial arms because they require fewer degrees of freedom of movement. Because legs tend to be used in a repeating pattern when walking, powered prostheses have usually been designed to sense the wearer’s movement and react to that; they haven’t been truly reactive to the amputee’s direct intentions. Now researchers from Rehabilitation Institute of Chicago (RIC) are reporting in the New England Journal of Medicine the development of a leg prosthesis that senses electromyographic (EMG) signals from already innervated and surgically reinnervated muscles of the thigh to control its motion.
The leg actually combines data about its position and movement along with the EMG signals to infer how the person wants the leg to move. The new leg automatically adjusts between different walking scenarios, moving appropriately whether climbing stairs, ramps, or just navigating a flat surface.
The case study focuses on RIC research subject Zac Vawter, a lower-limb amputee who underwent targeted muscle reinnervation surgery – a procedure developed at RIC and Northwestern University – in 2009 to redirect nerves from damaged muscle in his amputated limb to healthy hamstring muscle above his knee. When the redirected nerves instruct the muscles to contract, sensors on the patient’s leg detect tiny electrical signals from the muscles. A specially-designed computer program analyzes these signals and data from sensors in the robotic leg. It instantaneously decodes the type of movement the patient is trying to perform and then sends those commands to the robotic leg. Using muscle signals, instead of robotic sensors, makes the system safer and more intuitive.
“The bionic leg is a big improvement compared to my regular prosthetic leg,” stated Vawter. “The bionic leg responds quickly and more appropriately, allowing me to interact with my environment in a way that is similar to how I moved before my amputation. For the first time since my injury, the bionic leg allows me to seamlessly walk up and down stairs and even reposition the prosthetic by thinking about the movement I want to perform. This is a huge milestone for me and for all leg amputees.”
Report in New England Journal of Medicine: Robotic Leg Control with EMG Decoding in an Amputee with Nerve Transfers