Effects of the screw positions at the tibiofibular syndesmosis on the stress distribution at the ankle: a finite element analysis

Abstract

Objective To analyze the effects of 2 different screw positions on the stress distribution at the ankle in three-dimensional finite element models of screw fixation of the inferior tibiofibular syndesmosis.Methods Helical CT scan images of the right foot of a 30 year-old male volunteer were obtained.Software (Mimics,SolidWorks and Simulation) was used to reconstruct three-dimensional bone structures,to simulate ligamentous connections and to generate articular contacts in 3 finite element models of normal ankle,screw fixation for tibiofibular syndesmosis injury with screw placement at 2.5 cm and 5.0 cm above the tibiotalar joint respectively.Loads were applied in simulations of the ankle at the neutral position with single-foot standing,internal rotation and external rotation for calculation of the stress distributions at the ankle.Results Screw fixation with 2 different placement positions decreased the stresses on the periarticular ligaments of the ankle but increased the stresses on the crural interosseous membrane.The stresses on the fibular attachment point of the proximal crural interosseous membrane increased to 28.91MPa and 27.76MPa respectively in the load simulation under internal rotation of the ankle.The contact forces at the major articulations were reduced.The contact forces in the load simulation under internal rotation of the ankle decreased to 136.55N and 120.14N between the tibia and talus,and 42.68N and 39.33N between the fibula and talus; the contact forces in the load simulation under external rotation of the ankle decreased to 167.93 N and 158.17 N between the tibia and talus,and 39.47N and 40.21N between the fibula and talus,respectively.Conclusion The three-dimensional finite element models of screw fixation of the inferior tibiofibular syndesmosis show that 2different screw placement positions will lead to changes in the stress distribution at the ankle but the differences are not significant between the 2 positions. Key words: Internal fixation; Biomechanics; Finite element analysis; Inferior tibiofibular syndesmosis injury