American Society for Peripheral Nerve

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A Novel Use for Partial Skeletal Muscle Grafts in Regenerative Peripheral Nerve Interfaces for Prosthetic Control
Shoshana L. Woo, MD; Melanie G. Urbanchek, PhD; Xin Zheng, BS; Michelle Leach, PhD; Jana D. Moon, BS; Paul S. Cederna, MD; Nicholas B. Langhals, PhD
Plastic Surgery, University of Michigan, Ann Arbor, MI

Objective: Nonvascularized partial skeletal muscle grafts are notorious for their limited force-generating capacity and tendency to degenerate in the absence of reinnervation. Accompanied by peripheral nerve implantation, however, partial muscle grafts survive and transmit detectable electromyographic (EMG) signals capable of prosthetic control. Our study investigated partial muscle graft survival in the construction of regenerative peripheral nerve interfaces (RPNIs) and further characterized their electrophysiological properties across various muscle donor sites.

Methods: Twenty adult male F344 rats were assigned to 1 of 5 groups based on muscle graft type used for RPNI construction: 1) control-whole extensor digitorum longus; 2) partial biceps femoris; 3) partial rectus femoris; 4) partial lateral gastrocnemius; and 5) partial vastus medialis. Each graft of approximately 140-mg was transferred to the thigh, wrapped in small intestinal submucosa for tissue isolation, and implanted with the transected common peroneal nerve. After 4 months of RPNI recovery, in situ EMG and force testing were performed (Figure 1).

Results: Twelve of 16 partial muscle RPNIs demonstrated detectable EMG function at 4 months. Significant differences between control (n=4) and functional partial muscle RPNIs (n=12) included average mass (11842 mg vs. 6625 mg), EMG peak-to-peak amplitude (6.72.3 mV vs. 1.51.6 mV), and maximum tetanic force (729666 mN vs. 175154 mN) (Figure 2). RPNI mass was the overriding significant predictor of EMG peak-to-peak amplitude (p<0.01). After adjusting for RPNI mass, donor muscle selection showed no correlation with partial muscle EMG signal strength.

Conclusions: Partial muscle graft RPNIs transmit detectable EMG signals with a 75% success rate at 4 months. This proof of concept underscores the potential to develop and refine partial muscle graft-based interfaces to harness peripheral nerve signals for high-fidelity prosthetic control.
Acknowledgments: This work was supported by DARPA (N66001-11-C-4190), the Plastic Surgery Foundation, and the Frederick A. Coller Surgical Society.

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