Research ArticleNEUROPROSTHETICS

Proprioception from a neurally controlled lower-extremity prosthesis

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Science Translational Medicine  30 May 2018:
Vol. 10, Issue 443, eaap8373
DOI: 10.1126/scitranslmed.aap8373

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A leg up for neuroprosthetics

Amputation severs bone, nerves, and muscles used for limb movement, limiting an amputee’s ability to sense and control a prosthesis. Here, Clites et al. tested autologous muscle-nerve interfaces created at the time of below-knee amputation in a human subject. Compared to four subjects with traditional amputations, the subject who received two agonist-antagonist myoneural interfaces in his residuum (which were connected via synthetic electrodes to his powered prosthesis) exhibited greater joint placement control and reflexive behavior during stair walking. The subject noted little delay between intentional activation of the muscles in his residuum and movement of his prosthesis and expressed a strong sense of embodiment (identifying the prosthesis as part of him). Agonist-antagonist myoneural interfaces could help restore natural sensation to prosthetic joints.

Abstract

Humans can precisely sense the position, speed, and torque of their body parts. This sense is known as proprioception and is essential to human motor control. Although there have been many attempts to create human-mechatronic interactions, there is still no robust, repeatable methodology to reflect proprioceptive information from a synthetic device onto the nervous system. To address this shortcoming, we present an agonist-antagonist myoneural interface (AMI). The AMI is composed of (i) a surgical construct made up of two muscle-tendons—an agonist and an antagonist—surgically connected in series so that contraction of one muscle stretches the other and (ii) a bidirectional efferent-afferent neural control architecture. The AMI preserves the dynamic muscle relationships that exist within native anatomy, thereby allowing proprioceptive signals from mechanoreceptors within both muscles to be communicated to the central nervous system. We surgically constructed two AMIs within the residual limb of a subject with a transtibial amputation. Each AMI sends control signals to one joint of a two-degree-of-freedom ankle-foot prosthesis and provides proprioceptive information pertaining to the movement of that joint. The AMI subject displayed improved control over the prosthesis compared to a group of four subjects having traditional amputation. We also show natural reflexive behaviors during stair ambulation in the AMI subject that do not appear in the cohort of subjects with traditional amputation. In addition, we demonstrate a system for closed-loop joint torque control in AMI subjects. These results provide a framework for integrating bionic systems with human physiology.

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