Mystacial Pad Allotransplantation: A Novel Vascularized Composite Allotransplantation Model for Evaluating Functional Recovery

Background: Current methodological approaches in vascularized composite allotransplantation (VCA) research demonstrate significant limitations in functional recovery assessment, necessitating endpoint histological evaluation and exhibiting inadequate correlation with human hand transplantation physiology. This investigation establishes a novel mystacial pad transplantation (MPT) model incorporating advanced neuroimaging technologies to enable comprehensive real-time functional assessment of sensorimotor recovery mechanisms. Methods: Fifteen 8–12-week-old Lewis rats underwent allogeneic orthotopic MPT from Brown Norway donors with serial evaluations extending to 3 months post-transplantation. Functional recovery assessment utilized blood oxygen level-dependent (BOLD) functional magnetic resonance imaging to evaluate cortical activation patterns. Vascular integrity was monitored through high-resolution ultrasound biomicroscopy, while peripheral nerve regeneration was quantified through histomorphometric assessment of myelinated axon density at neural coaptation sites. Results: Surgical procedures achieved an 80% success rate with standardized microsurgical techniques. BOLD signal responses demonstrated significant cortical activation (p-values ranging from 10⁻⁵ to 10⁻⁸) in contralateral S1BF, S2, and S1ULp regions. Ultrasound biomicroscopy revealed patent vascular anastomoses without transplant vasculopathy throughout the observation period. Histomorphometric quantification demonstrated 11% and 37% myelinated axon reduction at coaptation and distal sites respectively, with electron microscopic examination confirming successful nerve regeneration characterized by appropriate Schwann cell presence and robust myelination patterns. Conclusions: The mystacial pad transplantation model provides validated methodological capabilities for investigating functional recovery mechanisms in vascularized composite allotransplantation research through real-time assessment integration, with demonstrated correlation between incomplete anatomical regeneration and substantial functional recovery indicating cortical neuroplasticity compensation mechanisms that inform clinical transplantation outcome optimization strategies.