Abstract: BACKGROUND: Of ankle sprains and ankle ligament injuries, nearly 85% involved the lateral collateral ligaments, and the mechanism of injury was ankle varus during plantar flexion. Between 20% and 40% of patients with acute lateral ankle sprains develop persistent pain and chronic lateral ankle instability, resulting in excessive translation and rotation of the talus, accelerated cartilage wear and joint degeneration.
OBJECTIVE: To explore the effects of different types of lateral ankle collateral ligament injury models on ankle joint stability and contact strain of talus dome cartilage through finite element modeling. 
METHODS: The DICOM file of CT scan data of the ankle joint of a 27-year-old volunteer was imported into the finite element software for three-dimensional reconstruction and surface fitting, and then mesh division was carried out to establish a complete finite element model of the ankle joint containing bones, articular cartilage and ligaments. The changes of the ankle joint stability and talus cartilage contact strain were compared under four different conditions: normal, anterior talofibular ligament injury, calcaneofibular ligament injury and anterior talofibular ligament + calcaneofibular ligament injury. 
RESULTS AND CONCLUSION: (1) In the anterior drawer test, the anterior talar translation of anterior talofibular ligament injury and anterior talofibular ligament + calcaneofibular ligament injury was significantly greater than that of normal and calcaneofibular ligament injury (P < 0.05), but there was no significant difference between anterior talofibular ligament injury and anterior talofibular ligament + calcaneofibular ligament injury and between normal and calcaneofibular ligament injury (P > 0.05). (2) In the talus tilt test, the talus tilt angle of calcaneofibular ligament injury and anterior talofibular ligament + calcaneofibular ligament injury was significantly larger than that of normal and anterior talofibular ligament injury, but there was no significant difference between calcaneofibular ligament injury and anterior talofibular ligament + calcaneofibular ligament injury, and between normal and anterior talofibular ligament injury. (3) In the unipedal standing test, compared with the normal model, the above three injury models changed the contact strain distribution of talus dome cartilage and shifted the peak value from the anterolateral side to the anteromedial side of the talus dome, resulting in the increase of anteromedial pressure of talus dome cartilage, and the comparison of the peak values was: anterior talofibular ligament + calcaneofibular ligament injury > anterior talofibular ligament injury > calcaneofibular ligament injury > normal, and the peak value of anterior talofibular ligament + calcaneofibular ligament injury was significantly higher than that of anterior talofibular ligament injury and calcaneofibular ligament injury. (4) The results confirmed that the injury of the lateral collateral ligament of the ankle would lead to the loss of ankle stability and the increase of peak contact strain of anterior medial cartilage, revealed the relationship between chronic lateral ankle instability and ankle osteoarthritis, and concluded the necessity of repairing or reconstructing anterior talofibular ligament and calcaneofibular ligament, which provided a theoretical basis for surgical treatment of chronic lateral ankle instability. 

Key words: ankle lateral collateral ligament, ankle joint, finite element, biomechanics, anterior talofibular ligament, calcaneofibular ligament