Finite Element Mechanical Analysis Of Different Types Of Atlantoaxial Subluxation In Young Children

Objective:（1）To establish a C₀-C₂three-dimensional finite element model of occipitoatlantoaxial complex（OAC）and atlantoaxial subluxation（AARS）in children,and to observe and analyze the stress of each tissue structure under different working conditions by finite element method.（2）The purpose of this study is to study the influence factors and degree of stress on bone,joint and related ligaments caused by atlantoaxial subluxation in the occipital atlantoaxial complex,and to provide theoretical basis for clinical treatment of various types of atlantoaxial subluxation in the occipital atlantoaxial complex in young children.Methods:By establishing four geometric models of atlantoaxial subluxation in young children,meshing,reconstructing the occipitoatlantoaxial complex and atlantoaxial joint-related bone（including bone compact,bone cancellous,cartilage,bone-cartilage junction,articular process,etc.）and related ligaments and other structural grids,and performing mechanical calculation and stress analysis.Results:The atlanto-occipital subluxation types of the four Fielding-Hawkins subtypes were successfully modelled and the maximum Mises stresses in the C₀,C₁and C₂vertebral segments were found to exist in the atlanto-occipital collateral ligament in the anterior flexion,posterior extension,left flexion,right flexion,left rotation and right rotation conditions.It was found that the atlanto-occipital collateral ligament had the maximum vertebral stress value in anterior flexion,the interatlanto-occipital ligament had the maximum vertebral stress value in posterior extension,and the atlanto-occipital tuberosity had the maximum stress in left flexion,right flexion,left rotation and right rotation;the maximum tensile stress of the ligaments related to the occipito-atlanto-axial complex was found to exist in the collateral ligament in anterior flexion and the apical ligament of the odontoid in posterior extension,and the transverse atlanto-occipital ligament in left flexion,right flexion,left rotation and right rotation The maximum tensile stresses were found in the transverse atlantoaxial ligament in left lateral flexion,right lateral flexion,left rotation and right rotation.Conclusion:（1）In this study,four finite element models of International Fielding-Hawkins classification were successfully established,and mechanical analysis could be carried out under six loads of flexion and extension,lateral flexion and rotation.（2）The overall stress cloud diagram showed that the stress concentration points of C₀,C₁and C₂were located at the junction of the middle and lower 1/3 of the axis vertebral body under the conditions of flexion,extension,lateral flexion,right flexion,left rotation and right rotation,and there was another stress concentration point located on both sides of the anterior arch of the atlas under the rotation condition.（3）The maximum Mises stress under each working condition in the four types:the maximum Mises stress was located in the atlanto-occipital ligament during flexion;during extension,they were located in the atlantooccipital ligament,and C₂was located at the bottom of the vertebral body.Under the conditions of left flexion,right flexion,left rotation and right rotation,it was located in the atlanto-occipital joint,and C₂was still located at the bottom of its vertebral body.（4）The maximum tensile stress of the ligament in the four types:in the flexion condition,it is located in the nuchal ligament;in the extension condition,it is located in the apical ligament;in the lateral flexion and rotation conditions,it is located in the transverse ligament of the atlas.（5）The stress cloud diagram of each type under different working conditions shows that the model can successfully simulate the occipitoatlantoaxial complex of 5-year-old children.The geometric similarity is good,and the model is real and effective,which provides theoretical basis for different internal fixation methods and rehabilitation brace design.