Targeted muscle reinnervation attenuates neuropathic pain and neuroma development in a rat model of tibial nerve transection.

BACKGROUND: Peripheral nerve injuries often lead to painful neuroma formation and chronic neuropathic pain, and the optimal surgical strategy for prevention remains debated. Targeted muscle reinnervation (TMR), regenerative peripheral nerve interfaces (RPNI), and nerve-in-muscle implantation (NIM) are surgical techniques developed to mitigate neuroma-related pain, but their relative efficacy has not been compared systematically. This preclinical study compared TMR, NIM, and two RPNI variants in a rat tibial nerve transection model to identify which approach best reduces neuroma formation and pain. METHODS: Sprague-Dawley rats underwent right tibial nerve transection and were randomized into five groups: control (no repair), NIM, W-RPNI (wrapped RPNI), E-RPNI (embedded RPNI), or TMR. Behavioral outcomes including gait analysis (CatWalk), mechanical hypersensitivity (von Frey test), thermal hyperalgesia (Hargreaves test), and neuroma tenderness were assessed over 12 weeks. At week 12, distal nerve stumps and L4-L5 dorsal root ganglia (DRG) were harvested for histological evaluation, immunohistochemistry/immunofluorescence, and molecular analyses (qRT-PCR and Western blot) targeting pain- and inflammation-related biomarkers. RESULTS: By 12 weeks, TMR-treated rats showed the most robust improvements, including significantly longer stance duration, larger paw contact area, near-baseline withdrawal thresholds, and minimal neuroma tenderness, whereas untreated controls developed gross neuromas and persistent hypersensitivity. TMR also preserved organized nerve architecture with orderly axonal regeneration and minimal collagen I/III fibrosis at the stump. Molecular assays confirmed that TMR markedly attenuated nociceptive and inflammatory signaling, with TMR rats exhibiting the lowest expression of pain-related mediators (c-Fos, TRPA1, TRPV1, CGRP, NPY, BDNF) and pro-inflammatory/fibrotic markers (galectin, α-SMA, IL-1β, TNF-α, TGF-β) in nerve and DRG tissues. Conversely, the anti-inflammatory cytokine IL-10 and axonal ion pump subunits ATP1A2/ATP2B1 were significantly upregulated with TMR. Outcomes for the two RPNI groups were similar to each other and generally intermediate between TMR and control. CONCLUSION: TMR was superior to RPNI variants and NIM in preventing neuroma formation and alleviating neuropathic pain in this animal model. These findings support TMR as a promising surgical strategy to mitigate post-amputation neuroma pain.