Plastic Surgery Research Council
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PSRC 60th Annual Meeting
Program and Abstracts

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Adjacent Antagonistic RPNIs produce Independent Signaling for Prosthesis Control
Andrej Nedic, MSE, Daniel Ursu, MS, Ian Sando, MD, Jana Moon, BS, Cheryl Hassett, BS, R Brent Gillespie, PhD, Nick Langhals, PhD, Paul Cederna, MD, Melanie Urbanchek, PhD.
University of Michigan, Ann Arbor, MI, USA.

PURPOSE:
Regenerative Peripheral Nerve Interfaces (RPNIs) are neurotized muscle grafts that transduce peripheral nerve action potentials into electrical signals suitable for prosthesis control. A single RPNI controls a single movement. At least two independent RPNIs are required for agonist/antagonist control; however, it is unknown whether signals from adjacent RPNIs are independent. Our purpose was to determine whether two, adjacent RPNIs, with one neurotized by a foot dorsi-flexor nerve and the second neurotized by a foot plantar-flexor nerve produce independent signaling, capable of simultaneous prosthesis control.
METHODS:
RPNI (n=3) and Control (n=4) rats were studied. RPNI rats had two muscle units grafted from the left hind limb to the ipsilateral thigh; one was neurotized with the transected tibial nerve, the other by the transected peroneal nerve. Both RPNI units had bipolar electrodes sutured onto the muscle. Control rats had bipolar electrodes implanted onto the soleus and extensor digitorum longus left leg muscles. While walking on a treadmill, rats were videographed and raw EMG signals were simultaneously recorded. Video and EMG recordings were synchronized to gait phases. Rectified EMG was integrated, normalized to time, and expressed as percent of total stepping cycle activity for each stance and swing. Data are 16 stepping cycles for each rat.
RESULTS:
EMG activity for RPNI and Control rats displayed alternating patterns of activation during stance and swing (Fig 1). As expected, we found significantly greater tibial nerve (plantar-flexor) activity during stance compared to swing and greater peroneal nerve (dorsi-flexor) activity during swing compared to stance for RPNI and Control rats (p<0.00001) (Fig. 2). Out of 96 stepping cycles the tibial nerve reinnervated RPNI was active 95 times and the peroneal nerve reinnervated RPNI was active 92 times--99.0% and 95.83% sensitivity, respectively. Independence was found for RPNI activation by comparing tibial nerve reinnervated muscle activity during stance to peroneal nerve reinnervated muscle activity during stance. The strength of the significant difference indicates signaling is independent (p<0.00001). The same significant difference was found for tibial nerve reinnervated RPNI swing compared to peroneal nerve reinnervated RPNI swing (p<0.00001). Independent activity was also found for the Control group muscles.
CONCLUSION:
Adjacent RPNI units, tibial nerve reinnervated RPNI muscle and peroneal nerve reinnervated RPNI muscle, independently activate during quadripedal stepping cycles. Sensitivity of activation was excellent indicating the RPNI will activate when expected. These data support RPNI independence and the feasibility of using RPNIs to provide agonist/antagonist signaling for dexterous prosthetic control.
ACKNOWLEDGEMENT:
DARPA (N66001-11-C-4190).


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