American Society for Peripheral Nerve

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Strategy For The Implementation Of Agonist-Antagonist Myoneural Interfaces In Amputated Residua
Shriya S Srinivasan, BS1; Maurizio Diaz,1; Matthew J. Carty, MD2; Hugh Herr, PhD1;
1Massachusetts Institute of Technology, Cambridge, MA, 2Division of Plastic Surgery, Brigham and Women's Hospital, Boston, MA

The agonist-antagonist myoneural interface (AMI) is comprised of paired muscles coapted by the tendons, such that the contraction of one muscle stretches the other. By preserving dynamic muscle relationships, the AMI allows mechanotransducers to generate afferent proprioceptive signals. Preliminary evidence from a human participant suggests that AMIs have the capacity to provide high fidelity control of a prosthetic device, force feedback, and natural proprioception; however, this technique has only been performed in a planned amputation. In this study, we investigate a dual-stage surgical procedure that enables the implementation of the AMI in patients who have already undergone a standard amputation, where definitive intraoperative identification of discrete motor fascicles may be difficult.

AMIs were constructed using single and dual stage methods (n=5, murine model). In the first surgery of the dual-stage method, the sciatic nerve was transected and dissected. Each branch was placed into a free muscle graft and secured to superficial fascia, in close proximity to the predicted antagonist graft. After a brief period of reinnervation, extensor-flexor grafts were identified and linked to form an AMI in a subsequent surgery. Five weeks post-operatively, we performed electrophysiological, mechanical and histological studies to evaluate the ability of the AMIs to perform efferent and afferent signaling, and generate proportionally coupled strains.

Mechanical, electrophysiological and histological evidence showed that a dual-stage surgery was viable in creating AMIs capable of graded afferent/efferent signaling, with no significant difference from the single-stage group. Strain rates, atrophy, and reinnervation were not negatively impacted by a dual-stage approach. Graded force production further validated the ability of the dual-stage AMI to overcome any limiting contractile conditions of the muscle, including elasticity/compliance constraints due to scarring and minimized fiber length. We elicited H-waves in regenerative grafts, suggesting the incorporation of the AMI into physiological reflexive loops.

The dual-stage surgical method makes possible the creation of regenerative AMIs from unidentified nerve fascicles for multiple prosthetic DOF within a residual stump. Results demonstrate robust healing, revascularization, reinnervation and graded efferent and afferent signaling of AMIs. This surgical method represents a step towards restoration of dynamic functionality for persons with amputation to potentially avail bidirectional prosthetic control and natural proprioceptive feedback.

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