Abstract: BACKGROUND: Ligament rupture and defect of the lateral or medial malleolus caused by high-energy injuries are common challenges in foot and ankle surgery. Their neighboring core tendons are often used as grafts to reconstruct the deficient ligaments. It is of paramount importance to investigate the mechanical properties of such tendons in the context of ligament defects to provide a suitable donor tendon.
OBJECTIVE: To investigate the interactive dynamics and biomechanical alterations among their core tendons during ankle joint motions under varying degrees of lateral or medial malleolar ligament defect.
METHODS: Based on CT imaging data of the left foot of a 50-year-old healthy male, a surface stereolithography model was extracted and constructed using MIMICS software. After Geomagic Wrap software was employed to fit the surfaces, a bone-cartilage-ligament-tendon ankle complex model incorporating varying degrees of ligament deficiencies was created within SOLIDWORKS software. Finite element analysis was then conducted using Ansys Workbench software, and the model’s validity was verified through a simulated anterior drawer test. Following validation, the mechanical response of the ankle under the conditions of internal and external rotation, as well as inversion and eversion, was simulated. The variation and distribution patterns of the maximum Von-Mises stress in the peroneus brevis and longus tendons, as well as the anterior and posterior tibial tendons, were observed.
RESULTS AND CONCLUSION: (1) In the anterior drawer test, the maximum talar displacement reached 5.208 5 mm, which was similar to the data in the previous literature, thereby the effectiveness of the model was validated. (2) Under four loading conditions, the defect of unilateral single-bundle ligaments exerted minimal influence on the maximum stress of adjacent core tendons, whereas the defect of unilateral multi-bundle ligament significantly increased the maximum tendon stress. Except for the consistently high stress across segments of the anterior tibial tendon, the high-stress regions in the long and short peroneal tendons and posterior tibial tendon were concentrated at their distal ends near the insertions. (3) Regarding the defect of the lateral malleolar ligament, the maximum stress and its variation in the peroneus brevis tendon during inversion and internal rotation were higher than those in the peroneus longus tendon. During inversion under the condition of the defect of the anterior talofibular ligament, the maximum stress in the short peroneal tendon increased by 0.951 2 MPa compared to that of normal condition, while that in the long peroneal tendon decreased by 0.065 1 MPa. Under the condition of the defect of the calcaneofibular ligament during internal rotation, the maximum stress in the short peroneal tendon increased by 2.352 9 MPa, while the maximum stress in the long peroneal tendon decreased by 0.269 2 MPa. (4) During eversion and external rotation under the defect of medial malleolar ligament, the variations in the maximum stress of the anterior and posterior tibial tendons were complex and depended on the type of ligament defect. Notably, full-thickness ligament defect significantly augmented the maximum stress in both tendons.

Key words: ankle joint, tendon, ligament defect, neighboring core tendon, finite element analysis, biomechanics