| [Objective]The biomechanical characteristics of three different posterior atlantoaxial nail implantation methods in the upper cervical spine under the condition of severe osteoporosis（SOP）were analyzed by finite element method,To provide biomechanical theoretical basis for the selection of surgical procedures for atlantoaxial（C1-C2）instability patients with SOP.[Methods]CT scan of upper cervical spine was performed in a healthy adult male,and the images were obtained.Through mimics19.0、Geomagic Studio2017、Abaqus6.14-3 and other relevant medical image software,process CT images,divide grids,assign materials,establish a normal upper cervical finite element model,and verify the effectiveness of the model.Then,through the finite element preprocessing software,reset the material properties,remove the atlantoaxial transverse ligament and cruciate ligament,and simulate the atlantoaxial（C1-C2）instability model of SOP.Based on the C1-C2instability model of SOP,three different methods of posterior atlanto bilateral pedicle screw（B-C1PS）+axial screw implantation were established:Bilateral pedicle screw of axis（B-C2PS,model A）;Bilateral lamina screws of axis（B-C2TL,model B）;B-C2PS combined with B-C2TL（model C）.The C1-C2joint range of motion and C1displacement of the three models under flexion,extension,lateral bending and axial rotation were analyzed,and the stress distribution of C2screws on different internal fixation models was studied by extracting stress nephogram.[Results]The established normal upper cervical spine model C1-C2joint range of motion has a good correlation with the experimental data of previous published articles,and the model verification is effective.On the C1-C2finite element model of SOP,there was significant difference in C1-C2joint range of motion between the three internal fixation models and the instability model（P<0.05）.The C1-C2joint motion of model C under flexion and extension、side bending and rotation conditions is reduced by0.8%,8.5%and 4.4%respectively compared with model A,and 13.6%,12.7%and 3.5%respectively compared with model B;The displacement of C1under different working conditions of internal fixation model C is smaller than that of internal fixation models A and B.On the C1-C2instability finite element model of SOP,the stress nephogram of three internal fixation methods shows that the maximum stress of axis screw under combined fixation of C2screw is smaller than that of single fixation:the maximum stress value of model C axial lamina screw under each working condition is less than that of model B lamina screw,and the maximum stress value of model C axial pedicle screw under each working condition is less than that of model A pedicle screw.The stress distribution of model C is mainly concentrated in the root of C2PS and the connection between atlantoaxial pedicle screw and screw rod.[Conclusion]Under SOP conditions,model C internal fixation is more stable than models A and B,and the range of motion and displacement of atlantoaxial joint are smaller.Compared with models A and B on the stress nephogram,the maximum stress of model C axial screw under different working conditions is dispersed,which is less prone to postoperative fatigue loosening and prolapse than model A and B axial screws.Model C can be used as a surgical option for patients with C1-C2instability complicated with SOP... |
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