By establishing a three-dimensional finite element model of ankle injury arising from supination and external rotation, the stress characteristics of the posterior malleolar surface can be obtained, and analysis of the corresponding stress on the lateral ankle can be conducted. Thin-layer computed tomography images of normal ankle joint in the supination and external rotation nonweight-bearing states was selected, to construct a three-dimensional data model of each ankle joint. A load was applied to examine different ankle joint stress values and pressure distributions on the surface of the posterior ankle joint. A 600 N vertical compressive and 10 Nm internal rotation load was applied in Stage III (removing the anterior tibiofibular ligament and the posterior tibiofibular ligament) of SER (supination-external rotation). When the lateral malleolar was intact, 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 malleolar surface was lower than 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 malleolar surface was 8.022 MPa. This study shows that reconstruction of the lateral malleolus in supination-external rotation ankle injuries significantly affects the stress distribution at the posterior malleolar joint surface. Through this reconstruction, the pressure distribution of the posterior malleolar joint surface can be significantly reduced.

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 conducted.Methods Thin-layer computed tomography (CT) images of normal ankle joints in the supination and external rotation nonweight-bearing states were selected, a three-dimensional data model of each ankle joint, including the ligament, was established, and whether different stages of injury coexisted 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 malleolar 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, upon which 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 disappearance of pressure concentration helps reduce the stresses associated with posterior ankle fracture. At this time, the rotational stress imposed by posterior ankle fracture is significantly higher than the vertical stress; the former should be the focus of clinician attention to ensure optimal healing.

No abstract