Three-Dimensional Finite Element Analysis Of Retropharyngeal Cervical Hook-Plate(RCHP)

ObjectiveTo establish a finite element model of the C_1-3-3 Retropharyngeal cervical hook-plate?RCHP?system and analysis the biomechanical properties such as stress distribution and three-dimensional activity of RCHP compared with the pedicle screw system to verify its biomechanical properties.Method1.A 27-year-old adult healthy male was selected as a volunteer,the CT data of his upper cervical vertebra?C0-C3?was collected and input into the cervical vertebra image into the 3D reconstruction software to perform reverse engineering reconstruction work.After a series of image processing such as smoothing,grinding and denoising,and establishing structures such as intervertebral disc and facet joint,a complete three-dimensional solid model of the upper cervical vertebra was generated.The obtained 3D model was meshed,the mesh quality was corrected afterwards.After the articular surface was extracted,the annulus fibrosus and nucleus pulposus were divided as well as the cartilage endpates were abstracted,a three-dimensional finite element model of the intact normal upper cervical vertebra complex was abtained.Compared with the results of in vitro biomechanical experiments of Panjabi et al^[1-3],the finite element model of the C0-C3 created by Brolin et al^[4]which was validated under the same loading conditions and boundary setting conditions,the validity of our model was verified.2.On the basis of establishing a normal and effective three-dimensional finite element model of C0-C3 vertebrae,model of lesion?defect?of axis vertebral body,the RCHP model,the nail rod model?atlas lateral mass screw+C3 pedicle screw model?were further established.The angular displacement of the four models was compared through the finite element method.Combined with C1-C3 and internal fixed stress data and stress cloud map to analyze the stress distribution,the biomechanical properties of C_1-3-3 RCHP and its internal stress distribution were analysed.Result1.Establishment and validation of finite element model of upper cervical spine:The normal upper cervical spine model was loaded with 1.5Nm load,the activities of the C0-C1 segment of the normal upper cervical finite element model under the conditions of flexion,extension,rotation and lateral flexion were 20.15°,18.80°,6.03°,8.56°,respectively.C1-C2 segments were 11.57 degrees,14.87 degrees,6.25degrees and 18.65 degrees,respectively,the C1-C2 segments are 11.57°,14.87°,6.25°,18.65°,respectively,the C2-C3 segments are 3.15°,2.05°,3.64°,1.27°,respectively.It was basically consistent with the literature data,which confirmed the validity and correctness of the normal upper cervical vertebra model.2.Finite element analysis of RCHP system for the treatment of lesion of axis vertebral body?such as tumors,tuberculosis,fractures,etc.?:The two sets of internal fixation models established on the defect model could effectively reduce the activity of C1-C2 and C2-C3segments and provide better stability.The RCHP model was reduced at C1-C2 by 88.6%,76.5%,96.2%,and 84.9%,respectively,under the conditions of flexion,posterior extension,lateral flexion,and rotation;at C2-C3 segment,the activity degree was reduced by 88.9%,93.0%,98.7%,and 86.5%in each working condition.The nail rod model was reduced at C1-C2 segment,and the mobility was reduced by 94.0%,99.5%,81.7%,and 92.7%under the conditions of flexion,posterior extension,rotation as well as lateral flexion,respectively.at C2-C3 segment,the activity-related pivot defect model was reduced by 96.9%,96.7%,98.4%,and 94.8%,respectively,under various conditions.The stability of the two internal fixation models was significantly stronger than the normal model and the defect model;compared with the nail bar model,the stability of the RCHP model was slightly stronger under lateral flexion conditions;but under the conditions of flexion,posterior extension and rotation,the stability of the RCHP model was slightly inferior to that of the nail rod model.In terms of stress,the maximum stress of RCHP under the conditions flexion,posterior extension,rotation as well as lateral flexion were 141.81Mpa,610.52Mpa,414.69Mpa and 238.39Mpa,respectively.The stress of the hook plate connection part is relatively stressed?including pressure,bending,twist?,and the stress peak was mainly located here.It means that the hook plate connection part is the relatively weak area of the RCHP.Conclusion?1?The finite element model of normal upper cervical spine established in this experiment is real and effective,and can be used for biomechanical research.?2?The hooked titanium plate model can be used to stabilize the lesions of the axis,its stability is weaker than the posterior nail rod fixation system under the conditions of flexion,posterior extension,and rotation.?3?The phenomenon of excessive local stress exists in the joint of hook plate,which provides a basis for further design and improvement.