| Background and ObjectiveAs a major difficulty in the treatment of irreducible atlanto-axial dislocation in upper cervical diseases,most patients have symptoms and signs of spinal cord compression of different degrees.There was no significant change in the dislocation of these patients in dynamic cervical x-ray position,and effective reduction could not be achieved by large-weight skull traction under preoperative routine and(or)general anesthesia.Up to now,there are no relevant finite element modeling cases.In this paper,we intended to explore the development method of three-dimensional nonlinear finite element model for irreducible atlanto-axial dislocation,and calculate the ranges of motion and stress distribution of the model under the position of flexion,extension,lateral flexion,and rotation,so as to provide reference of biomechanical data for subsequent scientific research and clinical development.Methods1.The finite element model was developed with detailed anatomy from high-resolution computed tomographic images of the occiput to the cervical C3 from a healthy male subject.The images data were saved in Dicom format,and then imported into the Mimics 21.0 software for reconstructing a three-dimensional geometric model of the upper cervical spine,and the model data files of different segments were respectively exported into STL format.They were then imported into the Geomagic 2021 software for surface treatment and characteristics optimized to develop a model with solid surface into which was imported SolidWorks 2021 software in STEP format for assembly and defect treatment.Finally,the finite element analysis software named Ansys 2021 was used to get the results.2.The three-dimensional ranges of motion of the model under various working conditions were compared with in vitro cadaver experiment and published literature data to verify the validity of the model.3.Based on the validated three-dimensional nonlinear finite element model of normal upper cervical spine and a typical clinical case,the primary model was modified carefully to develop a three-dimensional nonlinear finite element model of irreducible atlanto-axial dislocation combined with os odontoideum.Then we verified the validity of the model by comparing with the ranges of motion of the normal group as well as clinical data.ResultsWe successfully developed a three-dimensional nonlinear finite element model of normal upper cervical spine,of which validity had been verified.And on this basis,we successfully developed a three-dimensional nonlinear finite element model of irreducible atlanto-axial dislocation with os odontoideum named the pathological model,which was considered with good degree of imitation,according to a typical clinical case.It has 101019 units and 193726 nodes.There was no significant change in ranges of motion of the atlanto-occipital joint of the pathological model compared to the normal group in various working condition.The ranges of motion of atlanto-axial joint in flexion,extension and rotation of the pathological model were increased to different degrees compared to normal group,and the increment was respectively 3.1°,2.9°,9.9°(one side).The maximum stress of the pathological model were larger than those of the normal group during flexion,the increment was 2.25 MPa,which were located in the area near the joint surface of C2-3.The stress changes in different degree under other working conditions.ConclusionsThe model of irreducible atlanto-axial dislocation developped in this study based on the finite element method has good degree of imitation and is in line with the typical clinical case.The relevant modeling method can be used to help develop such complex models in the future.At the same time,the biomechanical data measured in this experiment can provide reference for subsequent scientific research and help clinicians to come up with more reasonable,effective and individualized therapeutic countermeasures. |
PDF Full Text Request