Continuous Facial Nerve Monitoring in Porcine Model: Analysis of Nerve Injury Mechanisms

Introduction: Facial nerve (FN) injury is a major source of complications in parotid gland and FN-related head and neck surgery, including common injury mechanisms such as traction injury, clamping injury, and thermal injury. This study aims to establish a porcine experimental model using continuous FN monitoring to demonstrate the electrophysiological and histological characteristics of different FN injury mechanisms.

Methods: In the experiment with live piglets (n=6), which included a total of 12 sides, there were 12 superior FN branches and 12 inferior FN branches were continuously monitored by NIM Vital system. The electromyographic (EMG) changes of the FN during clamping injury (n=2), thermal injury (n=2), and traction injury (n=2), the EMG changes during the 30-minute recovery period, and the histological findings of the injured nerve segment were analyzed. To evaluate the feasibility and accuracy of FN monitoring in porcine animal experiments in each side, branch, and mechanism.

Results: Continuous FN monitoring was successfully implemented in each FN branch, recording nerve injury and EMG signal changes within 30 minutes. For thermal and clamping injury, the EMG signals decreased rapidly and showed no significant improvement within 30 minutes. In contrast, traction injury showed a slightly longer onset of signal decrease, with a 23% to 75% signal recovery within 30 minutes. Histological results indicated an increase in lymphocytes around the injured nerves. In traction injury, structural damage was located in the epineurium area, whereas in clamping and thermal injury, structural damage can be located in the epineurium area, with more lymphocyte infiltration, and thrombus formation were observed.

Conclusions: In parotid gland and FN-related head and neck surgery, the electrophysiological and histological changes in common nerve injury mechanisms can be more comprehensively understood through animal experimental models. This study establishes the feasibility of a porcine animal model of FN injury that can subsequently be used as a model for quantifying nerve injury mechanisms.