Background
By establishing a three-dimensional finite element model of supination and external rotation ankle injury, the stress characteristics of the posterior ankle joint surface can be obtained, and complete analysis of the corresponding stress on the lateral ankle can be examined.
Methods
Thin-layer computed tomography (CT) images of normal ankle joints in the supination and external rotation non-weight-bearing states were selected, a three-dimensional data model of each ankle joint, including the ligament, was established, and whether different degrees of injury were coexistent with lateral ankle fracture was analysed by the finite element method. A load was applied to examine different ankle joint stress values and pressure distributions on the surface of the posterior ankle joint.
Results
When a load was applied, the maximum stress was located at the point of attachment of the anterior tibiofibular ligament to the tibia. When the anterior tibiofibular ligament was removed and the lateral malleolus was intact, the maximum stress (271.2 MPa) was located at the attachment point of the posterior tibiofibular ligament to the tibia, and the maximum pressure of the posterior ankle joint surface was 2.626 MPa. When a lateral malleolus fracture was present and the same load was applied, the maximum stress (82 MPa) was located on the fibular fracture surface, and the maximum pressure of the posterior ankle joint surface was 7.787 MPa. The posterior tibiofibular ligament was then removed completely from the lateral malleolus, and the maximum stress (132.7 MPa) was located at the point of attachment of the posterior tibiofibular ligament to the fibula, and the maximum pressure of the posterior ankle joint surface was 4.505 MPa. When a lateral malleolar fracture was present, the maximum stress (82.72 MPa) was located on the fibular fracture surface, and the maximum pressure of the posterior ankle joint surface was 8.022 MPa.
Conclusion
This study shows that reconstruction of the lateral malleolus in supination-external rotation ankle injury significantly affects the stress distribution at the posterior malleolar joint surface. When reconstruction of the lateral malleolus is complete, the pressure distribution of the posterior malleolar joint surface can be significantly reduced. The results highlight the significance of reconstruction of posterior malleolar fractures and posterior tibiofibular ligament stability.