Introduction <p>Ankle sprains are common sports-related injuries, and recurrent sprains may lead to chronic ankle instability (CAI). The mechanical and geometric properties of lateral ankle ligaments are crucial for joint stability. This study investigated how variations in Young’s modulus and thickness of the lateral ankle ligaments influence ankle stability.</p> Methods <p>A finite element model of the ankle was developed, in which the thickness and Young’s modulus of the anterior talofibular ligament (ATFL), calcaneofibular ligament (CFL), and posterior talofibular ligament (PTFL) were individually varied. Anterior stiffness and inversion stiffness were assessed via simulated anterior drawer and talar tilt tests.</p> Results <p>For the ATFL and PTFL, both anterior and inversion stiffness increased with greater Young’s modulus and ligament thickness. For the CFL, increases in Young’s modulus and thickness only enhanced inversion stiffness. The Young’s modulus–thickness–joint stiffness relationship for the ATFL was best described by a sigmoid-like curve, while those for the CFL and PTFL were best fitted with polynomial curves.</p> Conclusion <p>Variations in Young’s modulus and thickness of the ATFL, CFL, and PTFL significantly affect ankle joint stability. The fitted Young’s modulus–thickness–joint stiffness functions may provide valuable reference data for the clinical diagnosis and treatment of CAI.</p> Graphical Abstract <p></p>