| The upper cervical spine and occipito-cervical (joint between skull andatlas) have special anatomical structure, also known as the occipitoatlantoaxialcomplex (C0-C2). Its stability is mainly dependent on the ligaments and muscle,so its range of motion (ROM) is larger. The experimental data in literature showthat the ROMs of cervical spine in flexion/extension and axial rotation are40%and60%respectively, which are concentrated in the occipito-cervical withimportant physiological function. Development of modern transportationindustry, sports, and long-term chronic fatigue and other reasons lead to a lot ofcervical vertebra disease. Lesions of occipito-cervical include rheumatoidarthritis, cancer, and tuberculosis, etc. Trauma injury of occipito-cervicalincludes vertebral fracture, ligament, intervertebral disc rupture dislocation, etc.The upper cervical spine injury accounted for about50%of the entire cervicalspine injury, so it has become the focus of research in the field of spine surgery.The three-dimensional geometric model was reconstructed based on theCT images of upper cervical in Mimics10.01software. The finite elementmodel (FEM) of upper cervical spine was established by using ANSYS-ICEM,Hypermesh on the basis of geometric model. The finite element mesh was imported into ABAQUS6.11to perform finite element analysis (FEA). Verticalload of40N was applied on the occiput to simulate the head weight, besides,1.5N m torque was applied on the occiput to simulate loading conditions of flexion,extension, lateral bending, and rotation with constraints of all degrees offreedom in the inferior of C3vertebral body. ROM and distribution of von Misesstress were analyzed in different loading conditions (flexion, extension, lateralbending, and axial rotation). The established FEM of cervical spine wasvalidated by comparing with the in vitro experiment data and FEMs in literature.Based on the validated intact FEM of cervical spine, the internal fixation FEMof Anterior locking plate+Cage+Bone Graft (Plate+Cage), C2pediclescrews+C3lateral mass screws (C2PS+C3LMS) for Hangman fracture, occipitalplate+C1lateral mass screws+C2pedicle screws (C1LMS+C2PS), and occipitalplate+C2pedicle screws (C2PS) for occipitocervical fusion were established,which were also validated by comparing with the in vitro experiment data andFEMs in literature.The ROM of C0-C1segment of the intact upper cervical spine in flexion,extension, lateral bending, and axial rotation were11.3°,17.0°,3.8°,5.1°, thoseof C1-C2segment were13.9°,13.5°,5.1°,30.1°，and those of C2-C3segmentwere3.1°,3.5°,4.1°,2.5°respectively, which were in consistent with the data inliterature. Two groups of Hangman fracture internal fixation models caneffectively reduce the range of motion of C2-C3segment, which could producegood stability. In comparison with the results of unstable model, the Plate+Cage model could decrease the ROM by92.4%,97.1%,96.5%and90.0%, while theC2PS+C3LMS model could decrease the ROM by88.6%,90.2%,95.7%and90.3%in flexion, extension, lateral bending and axial rotation, respectively.Plate+Cage model had a better stability than C2PS+C3LMS model in flexionand extension, while they had similar stability in lateral bending and axialrotation. The peak stress of Plate+Cage model was less than that ofC2PS+C3LMS model in all loading conditions. Stress distribution and structureof Plate+Cage model was more reasonable than those of C2PS+C2LMS, whichcould achieve the reduction, decompression, fixation and fusion in one step.Thus it is an effective operative procedure for treating typeⅡ Hangman fracture.In comparison with the results of unstable model, the C1LMS+C2PS modelcould decrease the ROM by92.4%,97.1%,96.5%and90.0%, while the C2PSmodel could decrease the ROM by88.6%,90.2%,95.7%and90.3%in flexion,extension, lateral bending and axial rotation, respectively. The immediatestability of C1LMS+C2PS model was better than that of C2PS model, whichmay improve the fusion rate in the early postoperative recovery. Stressdistribution of C1LMS+C2PS model was more reasonable than that of C2PS, forwhich the implant may achieve longer service life in the long-term postoperativerecovery.In this thesis, the FEM has high geometric fidelity, which is closer to theactual cervical spine, and the internal fixation models for Hangman fracture andoccitocervical fusion were established to be applied to the biomechanical study of cervical spine. The FEA can quantify cervical motion and stress distribution,which could make up for the lack of in vitro cadaveric experiment, and providebasis for clinical application. |
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