Novel Surgical Technique Advances Proprioception

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A study, published in Science Translational Medicine on May 30, describes how a surgical agonist-antagonist myoneural interface (AMI) was used to give a subject with a transtibial amputation the sense of the position of his prosthetic limb and improved control over his prosthesis compared to a group of four subjects who had traditional amputation surgery.

The study's first author, Tyler Clites, a Massachusetts Institute of Technology (MIT) graduate student, recently won the Lemelson-MIT Student Prize for the AMI approach, a novel surgical technique for limb amputation and a complementary prosthetic control system that gave the subject proprioception, or the sense of the relative positioning of his  prosthesis.

The AMI is 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 a bidirectional efferent-afferent neural control architecture. The AMI preserves the dynamic muscle relationships that exist within native anatomy, allowing proprioceptive signals from mechanoreceptors within both muscles to be communicated to the central nervous system, according to the study.

The researchers surgically constructed two AMIs within the subject's residual limb. 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 study also described the subject's natural reflexive behaviors during stair ambulation, which  the other four subjects did not display. The study's authors note that their demonstration of a system for closed-loop joint torque control in AMI subjects provides a framework for integrating bionic systems with human physiology.