| BackgroundAnkle sprain is a common sports-related injury, which share a proportion of25%of the sports injury. As many as85%of the ankle sprains are caused by an inversion force, resulting in injury to the lateral ankle ligaments. The lateral ankle ligaments are important structures contribute to the stability of ankle. The injury of the anterior talofibular ligament (ATFL) and calcaneal-fibular ligament (CFL) will lead to a lateral instability of the ankle joint. Symptomatic ankle instability may develop in as many as20%of patients after a severe inversion ankle injury.The traditional orthopedic biomechanical experiment uses the animal model or cadaver specimens as object of the study. However, the proper animal model for ankle joint hasn't been established and the cadaver specimens are difficult to obtain. The cadaver specimen has great advantages in physical similarity, however, its biomechanical properties of the tissue changes gradually and different specimens have different biomechanical properties, which decreased the reliability of the control study.With the development of the computer technology, the finite element analysis (FEA) has soon become a modern method of the biomechanical studies. Such methods allow simulation of the forces acting on the model and approximate calculations of these forces at various points throughout the model. An advantage of such numerical studies lies in the precise control of loading, motions, boundary conditions and structural alterations in parametric studies of the joint response. Stress and strain in a structure can be solved exactly with analytical means for simple geometric shapes with homogenous material properties. Due to these reasons, the FEA method becomes an important supplement to the traditional biomechanical experiments.The geometry of the ankle joint was input into a MRI scan voxels, and then it was transformed into the elements of a high resolution FE model in the Mimics and ANSYS. The model includes the distal tibia and fibular, the whole talus and calcaneus and articular cartilage. The ligamentous structures were modeled with single or multiple link elements in the ANSYS. The anterior translation of the talus in the anterior drawer test was used for verification and sensitivity analysis. Ankles with injured and reconstructed ligaments were simulated. We tried to figure out which nonanatomic tenodesis reconstruction is the best method to cure the CAI. This test will provide a reliable theoretical basis for the treatment of CAI. Part one:The establishment and verification of finite element model of human ankle jointObjective:Construct a3-diamensional finite element model of ankle joint and check the validity of the model, which provides a platform for the next study.Methods:Chose a healthy volunteer and used MRI to get spinal successive scanning with layer thickness of1millimeter of the ankle joint. The images were saved as a form of Dicom. Used the Mimics to form a3-diamensional geometric model of ankle joint, and divided mesh in Magics. Then imported the model into ANSYS and assign the mesh with specific materials attribute. The ligamentous structures were modeled with single or multiple link elements in the ANSYS. Compared the published data and predicted kinematics in the anterior drawer test. Use the anterior translations of the talus to do verification and sensitivity analysis.Results:1. The predicted anterior translation of the talus (ATT) in the anterior drawer test was similar to those data from previous experiments.2. The ATT decreased with the increase of the ankle flexion angle and the highest laxity of the ankle was detected in the neutral position. Only the anterior talofibular ligament (ATFL) cutting resulted in significantly increased laxity in our model. The ATFL was the primary ligament to resist the anterior drawer force.Conclusion:1. Based on Dicom document with MRI scanning, used software of Mimics and ANSYS, we constructed a finite element model of ankle joint. The model included the distal tibia and fibular, the whole talus and calcaneus, articular cartilage and the ligaments surround the ankle joint.2. Comparisons between published data and the predicted kinematics under similar conditions demonstrated its good performance and accuracy. The sensitivity analysis of the model showed it was sensitive to the change of the parameters of the ligament. It provides a digital platform for the next study.Part two:The finite element analysis of the lateral ligaments' biomechanical contribution to the ankle stabilityObjective:To make use of the model constructed in upper chapter in analyzing the lateral ligaments' biomechanical contribution to the ankle stability.Methods:1. Removing the lateral ligaments to simulate the lateral ligaments injured ankle. 2. Simulated the ADT:applied an incremental anterior force from50N up to150N on the calcaneus with axial force on the tibia, calculated the ATT and the force in the ligaments.3. Limited the movement of the tibia and fibula, fix the ankle at different flexion angles, then applied an inversional torque of1.7NM on the calcaneus, calculated the talus tilt (TT) and the force in the ligaments.4. Limited the movement of the tibia and fibula, fix the ankle at different flexion angles, and then applied an internal rotational torque of3.4NM on the calcaneus, calculated the internal rotation angle of talus and the force in the ligaments.Results:1. Only the ATFL cutting resulted in significantly increased laxity in the ankle. The talocrural joint laxity is similar between the combined ATFL/CFL injured ankle and ATFL injured ankle. The difference in anterior drawer flexibility between injured and intact ankles significantly decreased when the axial load is bigger than300N. The ATFL carried the largest forces resisting the anterior drawer force.2. The inversonal instability significantly increased only when the CFL was injured. The injury of the ATFL will not lead to obvious inversonal instability. The CFL carried the largest forces resisting the inversional torque together.3. The internal rotation instability significantly increased when the ATFL was injured. The ATFL carried the largest forces resisting the internal rotation torque.Conclusion:1. The ATFL was the primary restraint to ADT motion at the ankle joint. Under an anterior drawer force of100N at neutral position, the ATT≥6mm and ΔATT>2mm suggest the injury of the ATFL2. The ankle has the largest laxity in the neutral position in the ADT. When the axial force is bigger than300N, the bony configuration became the major factor stabilized the ankle joint.3. The inversonal test was not sensitive to figure out the injury of the ATFL. The CFL was the major restraint to resist the inversion of the ankle. The inversional instability increased obviously only when the CFL was injured. The normal TT≤4°and TT≥12°suggest the injury of ATFL and CFL4. The ATFL was the primary restraint to internal rotation of the ankle. The normal TR≤4°and TR≥8°uggest the injury of ATFL.Part three:The finite element analysis of the Evans,Chrisman-Snook and Watson-Jones procedures in stabilizing the ankle joint for the patient of chronic ankle instability.Objective:Simulated the Evans,Chrisman-Snook and Watson-Jones procedures in the model of lateral ligament injured ankle. Compare the stability of the ankle with different nonanatomic tenodesis reconstruction.Method:1. According to the clinical approaches, construct the Evans, Chrisman-Snook and Watson-Jones reconstruction models.2. Simulated the ADT:applied an incremental anterior force from50N up to150N on the calcaneus, calculated the ATT in different reconstruction models.3. Applied an inversional torque of1.7NM on the calcaneus, calculated the TT and the force in the ligaments and reconstructed tendons.4. Applied an internal rotation torque of3.4NM on the calcaneus, calculated the TR and the force in the ligaments and reconstructed tendons.Results:All three reconstructions increased stability over the ATFL and CFL deficient state, but the effectiveness of each procedure was dependent on the direction of the stress applied (inversion, internal rotation or anterior translation) and the position of the ankle in dorsiflexion-plantarflexion. The Watson-Jones procedure had advantages with other nonanatomic tenodesis reconstruction methods. Conclusion:1. The Evans,Chrisman-Snook and Watson-Jones reconstruction models was successfully constructed based on the ATFL and CFL injured model.2. Finite element analysis showed that the Watson-Jones procedure had advantages with regard to anterior and rotational stabilities as well as ligaments and grafts stress in comparison with other nonanatomic tenodesis reconstruction methods.3. No nonanatomic tenodesis reconstructions could completely restore the values for ankle flexibility to normal. The nonanatomic tenodesis reconstructions could not be chosen as the first choice in the treatment of CAI.
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