Contribution of the Anterior Talofibular Ligament on Ankle Joint Stability: A Finite Element Study

Category: Ankle; Basic Sciences/Biologics Introduction/Purpose: Ankle sprains typically occur when the ankle twists inward, with 73% involving damage to the ankle's lateral ligaments, and 20-40% progressing to chronic ankle instability (CAI). Repairing the anterior talofibular ligament (ATFL) has shown favorable outcomes postoperatively for CAI, suggesting the crucial role of the ATFL in ankle stability. However, it still remains unclear how the ATFL contributes to ankle stability. The present study aims to clarify the contribution of the ATFL to ankle stability through a three-dimensional (3D) finite element analysis of an anatomical foot model. Methods: We constructed a 3D finite element model of the human foot by extracting foot bones and the outer surface of the foot from computer tomography images, which were then meshed with tetrahedral elements. Material properties of bones and soft tissues were assigned based on existing literature. Ligaments surrounding the ankle and foot joints, as well as the plantar aponeurosis, were represented using tension-only truss elements. Surface-to-surface contacts between bones were modeled with a frictionless contact approach. The proximal ends of the tibia and fibula were anchored in the space, while external forces were applied to the calcaneus in the anterior and medial directions. We calculated the resulting translational and rotational movements of the foot bones in response to these forces. To examine the role of the ATFL in ankle joint stability, we repeated the calculations with the ATFL removed from the foot model. Results: When anterior external forces were applied, both the intact and ATFL-removed models exhibited forward talus translation and inversion rotation. However, in the latter, these movements were notably more pronounced due to the absence of the ligament connecting the distal fibula to the talus in the anteroinferior direction. The talus exhibited differing displacement patterns from the early stages of forward loading in the ATFL-removed model. Similarly, under the medial external force, larger talus inversion was observed in the ATFL-removed model. The present study demonstrated that the ATFL plays a crucial role in maintaining stability of the ankle joint when external forces are applied in the forward and/or medial directions to the foot. Conclusion: The ankle joint movements observed in the ATFL-removed model were consistent with what is seen in clinical settings and supported by existing research. The direction of talar displacement during loading seems to be linked to the structure of the ATFL, suggesting ankle joint instability. These findings enhance our understanding of the effects of ATFL on CAI and may provide insights into the underlying pathology of ankle joint disorders associated with ATFL injury.