154. Functional Motor Restoration Following Chronic Axotomy With Delayed Regenerative Peripheral Nerve Interface (RPNI) in a Rat Model

PURPOSE: Approximately 2 million people in the United States are affected by limb loss, many of whom have physical impairments and activity limitations. The Regenerative Peripheral Nerve Interface (RPNI) is a surgical technique that allows individuals to restore extremity function by real-time control of myoelectric prosthetic devices. RPNI is created by implanting a transected peripheral nerve into an autologous skeletal muscle graft. Following amputation, the successful regeneration of axons across the injury site is critical, yet prolonged denervation from an appropriate distal target can severely compromise functional outcomes. Substantial delays in the implantation of RPNI may be detrimental to prosthetic control, leading to a progressive decline in the regenerative ability and meaningful functional recovery of chronically axotomized neurons. This study aimed to determine regenerative capacity and signal amplification ability of RPNIs implanted after 3 and 6 months of chronic axotomy in a rat model. METHODS: Eighteen Lewis rats were randomly assigned to one of three groups (n=6/group): (1) Prophylactic RPNI, (2) chronic axotomy with 3-month delayed RPNI, or (3) chronic axotomy with 6-month delayed RPNI. After a three-month maturation period, electrophysiologic analyses were conducted to record compound muscle action potentials (CMAPs). RPNIs were then harvested for immunohistochemistry and gene analysis to evaluate muscle reinnervation, the extent of axonal regeneration, and inflammatory markers and cellular senescence in the graft microenvironment. RESULTS: All RPNIs remained viable over the maturation period and the wet RPNI muscle weight did not differ between the groups (p=0.8174). Electrophysiological testing of RPNI recorded amplified CMAP amplitudes. No significant difference was observed in peak-to-peak CMAP amplitudes between prophylactic RPNI (14.07±1.67 mV), 3-month delayed RPNI (14.10±2.98 mV), and 6-month delayed RPNI groups (10.59±1.33 mV) (p=0.478). CONCLUSION: RPNIs can mitigate the adverse impact of chronic axotomy and elicit biologically amplified signals to restore extremity function in the setting of chronic axotomy and delayed treatment.