Biomechanical Integrity Following Hemimandibulectomy With Free Fibular Flap Reconstruction Under External Impact Loading - An In Vitro Study.

Abstract

Introduction: Hemimandibulectomy for aggressive mandibular pathology results in significant functional and structural loss, necessitating reconstruction. The fibular free flap, although the gold standard, introduces biomechanical disparities that may alter the mandible's response to traumatic forces. While previous studies have focused on masticatory stress, the impact of high-energy trauma remains underexplored. This study aimed to evaluate and compare the biomechanical response of normal and fibula-reconstructed mandibles to external impact forces using finite element analysis (FEA), focusing on stress distribution and fracture-prone regions.

Materials and methods: Computed tomography-derived three-dimensional models of a normal mandible and a fibula-reconstructed mandible post-hemimandibulectomy were developed. Standardised impact loads of 2000 N were applied at the symphysis and mandibular body. Material properties were assumed to be linearly elastic and isotropic, and von Mises stress (VMS) analysis was performed to evaluate load response patterns.

Results: The normal mandible demonstrated symmetrical stress distribution, with peak values at the bilateral condyles and predictable contralateral transfer under lateral loading. In contrast, the reconstructed mandible exhibited elevated and asymmetrical stress, particularly at the condylar necks, graft-host interfaces and fixation zones, indicating increased susceptibility to mechanical failure, especially under lateral loading.

Discussion: Fibula-reconstructed hemimandibles show distinct biomechanical vulnerabilities under high-impact loading, particularly at the graft-host interface and condyles. These findings highlight the need for reinforcement strategies, optimised fixation planning and patient counselling regarding trauma risk. Strategic reinforcement at the graft-host junction and consideration of condylar load redistribution may help reduce fracture risk under traumatic conditions.