A Novel Rat Model for Muscle Regeneration and Fibrosis Studies in Surgical Lip Repair

OBJECTIVE: Lip muscle undergoes suboptimal regeneration after surgical repair, but the mechanism underlying this observation remains obscure. This study provided a rat model to investigate lip muscle regeneration after surgical intervention. DESIGN: This work provided a detailed description of the rat orbicularis oris muscle anatomy, and a surgically injured model was established based on the muscle anatomy. MAIN OUTCOME MEASURES: Morphological and histological features of the rat orbicularis oris muscle were characterized. The processes of myogenesis and fibrogenesis were examined between the untreated and surgically injured groups. RESULTS: Rat orbicularis oris muscle is encapsulated by the vermilion and oral mucosa. Although it remains a thin layer of flat muscle with tight myocutaneous and myomucosal junctions, if accessed properly, the rat orbicularis oris muscle could be isolated as a cylindrical muscle bundle with considerable size, facilitating further surgical manipulations of the muscle fibers. Muscles in steady state and after surgical intervention demonstrated distinct molecular features in the myogenesis and fibrogenesis processes, which were quantifiable in tissue section analysis. CONCLUSION: The orbicularis oris muscle dissection procedures and injury model provided in this work clarify the rat lip muscle anatomy. The injury model offered a platform to analyze the effects of surgical interventions commonly used in lip repair on orbicularis oris muscle regeneration.