Exploring Reinnervation within the Regenerative Peripheral Nerve Interface Through the Perspective of the Neuromuscular Junction

Chang Gung Memorial Hospital, Linkou Branch, Taoyuan, Taiwan

Chen KW, Cederna P

INTRODUCTION: The Regenerative Peripheral Nerve Interface (RPNI) is a strategy for preventing neuromas after amputation and has the potential to act as a neural signal transducer, enabling amputees to control myoelectric prostheses. However, further investigation is needed to understand how neuromuscular junction (NMJ) innervation is established in RPNIs.

MATERIALS AND METHODS: RPNIs were conducted in C57BL mice utilizing free extensor digitorum longus (EDL) muscle grafts placed in the femoral region that were neurotized in different manners: 1) Traditional RPNI innervated by PN, 2) Double fascicular (DF) RPNI innervated by PN dividing into two fascicles and plugging in different locations of the muscle grafts. Control groups were in situ EDL muscles that had 3) intact PN innervation or 4) PN cut and primarily repaired. The endpoint assessments were conducted at 12 weeks postoperatively with target muscle weight measurement (mg), compound muscle action potential (CMAP) (mV), and whole-mount immunofluorescent (IHF) staining.

RESULTS: RPNI, when compared to the PN cut and repaired group, showed significantly decreased muscle weight (8.0 ± 1.4 vs 10.0 ± 1.0 mg) and CMAP (6.0 ± 1.7 mV vs 8.1 ± 0.6 mV) (p<0.05). DF- RPNI demonstrated target muscle weight (11.0 ± 2.1 mg) and CMAP (7.5 ± 0.6 mV) comparable to the healthy EDL muscles and the PN cut and repaired group. IHF staining showed 81.1% and 70.5 fully innervated NMJs in the healthy EDL and PN cut and repaired group; conversely, partially innervated NMJ was the main method of innervation in RPNI (44%) and DF-RPNI (53%).

CONCLUSIONS: Traditional RPNI showed decreased NMJ innervation with more partially innervated NMJs compared to the control groups but was sufficient to transduce neural signal. Dividing the neural source and implantation into different locations of the target muscle graft leads to improved muscle function.