Design And Finite Element Analysis Of Customized Atlantoaxial Lateral Mass Intervertebral Cage

Objective To design a customized atlantoaxial lateral mass intervertebral cage and evaluate its biomechanical properties to provide a reference for the development of an individualized surgical plan for patients with basilar invagination and atlantoaxial dislocation.Methods Collect thin-slice CT data of the upper cervical spine of a patient with basilar invagination and atlantoaxial dislocation,and use specialized 3D modeling software to reconstruct a geometric 3D model of the basilar invagination and atlantoaxial dislocation.First,simulate reduction to obtain a simple posterior instrumented occipitocervical fixation model,and then use reverse engineering to fit the shape and size of the lateral mass intervertebral cage to the reduced atlantoaxial facet joint,obtaining a personalized cage.Using finite element analysis,establish a finite element model(BI-AAD model)of the upper cervical spine(C0～C3)with basilar invagination and atlantoaxial dislocation,as well as an occipitocervical fixation finite element model(OF model),verifying the validity of the models.Calculate the range of motion(ROM)in the atlantoaxial segmental,vertebral displacement peak,Von Mises stress distribution of the occipitocervical fixation system,the customized cages,and atlantoaxial facet joint surfaces under six different conditions of flexion,extension,left and right bending,and left and right rotation for the OF+Cage model and compare it to the OF model.Results ROM of the atlantoaxial joint segment during various physiological neck movements predicted by the BI-AAD model and OF model showed similar results to previous research reports,indicating that the models are effective.The OF+Cage model demonstrated greater reductions in the ROM of the atlantoaxial joint segment after surgery during six different movements,including forward flexion,back extension,right and left lateral bending,and right and left rotation,with decreases of 95.52%,89.75%,96.27%,97.03%,98.07%,and98.04%,respectively,which were all greater than those observed in the OF model.The peak vertebral displacement decreased by 93.05%,88.55%,92.47%,94.06%,97.38%,and 97.55%,respectively,compared with the preoperative period,also compared with the OF model.Compared with the OF model,the peak stresses in the occipital plate were reduced by 27.43%to 94.17%,the titanium rods by 64.83% to 96.01%,and the pedicle screws by 45.11% to92.66% in the OF+Cage model under each direction of motion.The peak stresses of the custom-made cage in the OF+Cage model ranged from 7.53 MPa to 21.08 MPa,while the peak stresses observed in the articular surfaces of the lateral blocks of the cardinal vertebrae ranged from 4.10 MPa to 10.29 MPa.These stress levels were low,and no abnormal stress concentrations were observed.Conclusion Finite element models for upper cervical vertebrae(C0～C3)with basilar invagination accompanied by atlantoaxial dislocation,as well as for occipitocervical fixation,were successfully established and verified as effective for medical finite element analysis.The personalized design of the atlantoaxial lateral mass intervertebral cage was achieved through reverse engineering.Following reduction,there was a complete match between the cage and the atlantoaxial lateral mass joint.The biomechanical stability of the customized atlantoaxial lateral mass intervertebral cage is excellent.When combined with the occipitocervical fixation system,it significantly improves the stability of the atlantoaxial joint and reduces the stress level of the occipitocervical fixation system.Additionally,it has good anti-subsidence ability.