Biomechanical Effect Of Anterior Talofibular Ligament Injury In Weber B Lateral Malleolus Fractures After Locking Plate Fixation:A Finite Element Analysis

Objective: To determine the biomechanical effect of anterior talofibular ligament injury in Weber B lateral malleolus fractures after locking plate fixation.Method: A three-dimensional model was established based on CT images from a healthy volunteer.The simulation of lateral malleolus fracture,and the modeling and assembly of plate were completed by referring to characteristics of Weber B lateral malleolus fractures,as well as the technical characteristics of open reduction and internal fixation of lateral plate.Operating conditions were set up for groups A-D as follows: in group A,anterior&posterior inferior tibiofibular ligaments and anterior talofibular ligament all remained intact(ALL KEEP);in group B,anterior& posterior inferior tibiofibular ligaments were detached,while anterior talofibular ligament remained intact(CUT ATiF/PTiF);in group C,anterior&posterior inferior tibiofibular ligaments and anterior talofibular ligament were all detached(CUT ATiF/ATaF/PTiF);in group D,anterior& posterior inferior tibiofibular ligaments remained intact,while anterior talofibular ligament was detached(CUT ATaF).The proximal end of the model was restrained in all four groups,200 N of upward force and 100 N of backward force were applied at anterior of talus head in order to simulate the dorsiflexion of ankle joint.Biomechanical differences of the lateral plate were observed under various conditions of different ligament ruptures.Results: The maximum stress value of the plate in group A was the smallest,while that in group C was the largest.The maximum stress value in group B was larger than that in group A;and that in group D was obviously larger than that in group A.The location of maximum stress in group D was displaced from the posterior edge of the plate to the anterior edge of the plate,which was different from those in the other three groups.Conclusions: The anterior talofibular ligament injury is a major contributing factor to the stress of locking plate fixation following Weber B lateral malleolus fracture.It should be considered as an essential risk factor for evaluation of the stability in these fractures.