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Bilateral Regenerative Peripheral Nerve Interface Function Correlates with Hind Limb Kinematics during Treadmill Locomotion
Daniel Catalin Ursu, MS1; A. Nedic1, Cheryl A. Hassett, BS1; Jana D. Moon, BS1; Nicholas B. Langhals, PhD1; Richard B. Gillespie, PhD2; Paul S. Cederna, MD1; MG Urbanchek1
1Department of Surgery, Section of Plastic Surgery, University of Michigan, Ann Arbor, MI; 2Mechanical Engineering, University of Michigan, Ann Arbor, MI

Introduction: Regenerative Peripheral Nerve Interfaces (RPNIs) are neurotized autologous free muscle grafts equipped with electrodes to record myoelectric signals for prosthetic control. In vivo characterization of voluntary RPNI signaling is critical when designing prosthetic device controllers. RPNIs are known to reliably produce high fidelity electromyography (EMG); however, RPNI signaling has not been matched with joint movements during walking when foot flexor and extensor signals are provided by RPNIs. We seek to define the relationships between Control and RPNI group signaling using kinematics and joint gait analysis during volitional treadmill walking.

Methods: Three experimental groups of two rats were devised (Figure 1): Control, rat hind limbs remained intact; RPNI, rat left extensor digitorum longus and right soleus muscles were transferred to the ipsilateral thigh and reinnervated with the transected peroneal and tibial nerves, respectively; Denervated, rats underwent peroneal and tibial nerve transections. In all groups, bipolar wire electrodes were positioned on the muscles. Evaluations occurred 4-5 months post-surgery. Rats walked on a treadmill. A synchronized videography system was used to identify hip, knee, ankle, and toe joint angles bilaterally, with acquired EMG. Within each group, normalized joint angles and EMG were cross-correlated.

Results: Control and RPNI group EMG signals were periodic with gait. Control group hind limb movements were normal with normal EMG signal periodicity. RPNI and Denervated groups exhibited compensated gaits with marked inability to dorsiflex or plantarflex the left and right hind feet. RPNI signal periodicity had different timings from Control due to gait compensations (Figure 2). EMG was highly repeatable within rat and within left and right legs (Control: r=0.88; r=0.91) and (RPNI, r=0.75; r=0.79); but, RPNI signaling was of lower amplitude than controls. Cross-correlation of the EMG from Control and RPNI groups indicated RPNI signaling predicts peroneal and tibial nerve firing that is proportionally similar to Control. The Denervated group demonstrated low amplitude random signaling, unrelated to gait.

Conclusion: This study determined that in vivo EMG signaling of Control and RPNI rats is periodic and highly correlated with hind limb joint angles during walking. EMG signaling by RPNIs correctly matched with compensations during walking.

Acknowledgments: DARPA (N66001-11-C-4190)


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