Establishment and validation of finite element model of ossification of cervical posterior longitudinal ligament with intervertebral fusion

[Background ]: To establish a three-dimensional finite element model of ossification of the posterior longitudinal ligament of the cervical spine with intervertebral fusion and verify its effectiveness, and provide a platform for finite element calculation and biomechanical analysis in the later stage. [Method]: Select the Department of Spinal Surgery, Linfen People's Hospital A volunteer imported 719 DICOM format images of cervical spine CT scans into Mimics modeling software to build a preliminary 3D model in the stl format, and used Geomagic Studio 2013 software to refine and refine the 3D model to smooth out noise and generate NURBS surfaces The model was then imported into the finite element analysis software Ansys workbench 15.0, adding ligaments and intervertebral discs, meshing, assigning material properties, and simulating 6 activities of the human cervical spine, and comparing them with references. [Results]: A total of 7 Cervical vertebral body, 1 thoracic vertebral body, 5 intervertebral discs and ligaments, etc., with a total of 320512 nodes and 180905 units. It has a realistic appearance, high degree of detail reduction, and ossification of the cervical longitudinal longitudinal ligament with good geometric similarity Incorporate a three-dimensional finite element model of intervertebral fusion. In flexion and extension, left and right lateral flexion, and axial rotation activity compared with references, there is not much difference. [Conclusion]: OPLL merger interbody fusion dimensional finite element model has good mechanical and geometric similarity after similarity cervical established in this study, the model can provide a platform for the latter to further biomechanical analysis.

degree of detail reduction, and ossification of the cervical longitudinal longitudinal ligament with good geometric similarity Incorporate a three-dimensional finite element model of intervertebral fusion. In flexion and extension, left and right lateral flexion, and axial rotation activity compared with references, there is not much difference.
[Conclusion]: OPLL merger interbody fusion dimensional finite element model has good mechanical and geometric similarity after similarity cervical established in this study, the model can provide a platform for the latter to further biomechanical analysis.

Background
Ossification of posterior longitudinal lligament (OPLL) is a serious type of cervical degenerative disease. Epidemiological studies have shown that the incidence rate is high in Asian populations. The etiology is currently unknown. The pathogenesis is due to bone The compressed posterior longitudinal ligament compresses the spinal cord to produce a series of symptoms of spinal canal compression [1][2] . Mild patients can show numbness of the limbs, high muscle tone, and severe cases can form paraplegia. Osteosis of the posterior longitudinal ligament of the cervical spine often requires surgery. 3 It is divided into anterior and posterior approaches or anterior and posterior approaches.Because the ossification of the posterior longitudinal ligament of the cervical spine is different from the normal cervical spine, the biomechanical characteristics are complex [3][4] . May cause related complications [5] .CT tomographic images of volunteers with ossification of posterior longitudinal ligament of cervical spine and degenerative intervertebral fusion were collected in this study, and computer-aided engineering software (Mimics 17.0, Geomagic Studio2013, Ansys workbench 15.0) A structurally complete three-dimensional finite element model was established, which provided a reliable model basis for later biomechanical analysis.

Result
The three-dimensional finite element model of ossification of the posterior longitudinal ligament of the cervical spine and intervertebral fusion established in this study includes 7 cervical vertebral bodies, 1 thoracic vertebral body, 5 intervertebral discs, and ligaments, etc., a total of 320512 nodes and 180905 units. And the appearance is realistic, the degree of detail reduction is high, and it has very 5 good geometric similarity (Fig. 7). In the comparison of flexion and extension, left and right side bending, axial rotation activity and the literature, it can be seen that there is not much difference, which was established in this institute. The model's mobility is smaller than that of the reference, on the one hand, due to the ossification of the posterior longitudinal ligament of the cervical spine, which limits the mobility of the cervical spine, and on the other hand, due to cervical 5-6 intervertebral fusion.

Conclusion
OPLL merger interbody fusion dimensional finite element model has good mechanical and geometric similarity after similarity cervical established in this study, the model can provide a platform for the latter to further biomechanical analysis. The posterior longitudinal ligament is an internal structure of the spinal canal, starting from the pivot and lowering to the sacrum, covering the back of the vertebra, the front is the vertebra, and the back is the spinal cord. The ligament is wide and narrow, and the thoracic spine is thicker than the cervical and lumbar spines. The longitudinal ligament is wider in the intervertebral disc position and in close contact with the bone [4] .Compared to the anterior longitudinal ligament, the posterior longitudinal ligament is denser and firmer than the anterior longitudinal ligament.The function of the posterior longitudinal ligament is mainly to maintain the stability of the spine and limit excessive spine Flexion 6 and extension [10] . The etiology of ossification of the posterior longitudinal ligament of the cervical spine is still unclear, and may be related to trauma, chronic strain, inflammation, cervical disc degeneration, and genetic factors. The diagnosis of ossification of the posterior longitudinal ligament of the cervical spine mainly depends on cervical CT and three-dimensional Reconstruction [11] .In addition, cervical spine mri can observe the spinal cord compression and the severity of spinal cord disease, and predict the degree of spinal cord recovery after surgery.

Discussion
The ossification of the posterior longitudinal ligament of the cervical spine combined with intervertebral fusion is different from the normal cervical vertebra morphology and biomechanics.The specific manifestations are as follows: first, the patient's cervical spine physiological curvature straightens and even recurves; second, cervical mobility Declining, the fusion of the upper and lower segments of the intervertebral segment will accelerate degeneration, and the above reasons will cause changes in the cervical biomechanics of the patient; in addition, ossification of the posterior longitudinal ligament often requires surgery, and surgery will once again change the biomechanics of the patient's cervical spine. Opll surgical approach can be divided into anterior, posterior, and anterior and posterior approaches.For multi-segment ligament ossification, posterior approach is often chosen.Postoperative approach has the advantages of short operation time, less bleeding, and fewer complications. Whether it is a single door or a double door, the risk of cervical spine instability is greatly increased due to the damage to the posterior column [12] , cervical kyphosis will occur after surgery, and axial pain complications will occur. With the level of surgical technology With the continuous improvement of the anterior approach, the indications for anterior approach surgery are also expanding, and a new improved method [13] has appeared.Although anterior approach surgery There was no systematic theoretical support, and it included computer simulation modeling, biomechanical analysis, and surgical simulation drills. Digital medicine is particularly important for the formulation of scientific and personalized surgical strategies [14] . As early as the middle and late last century, digital medicine has emerged, and by the end of the last century, with the rapid development of information technology, digital medicine has With the rapid development, based on the assistance of digital medicine, it helps to diagnose and treat many diseases. With the formation of    [7] 53.05°±11.41°89.35°±18.07°B evilaqua [8] 57.56°±10.33°68.13°±11.28°T rott [9] 57.5°76.1°t his research 46.1°61.3° Table 3 Comparison of cervical scoliosis activity and literature data Author Left turn Right turn Tali [7] 47.70°±7.71°50.10°±5.33°B evilaqua [8] 45.64°±6.54°49.11°±6.27°T rott [9] 45.5°47.6°t his research 32.4°35.4° Table 4 Comparison of cervical spine model rotation and literature data 12 Author Rotate left Rotate right Tali [7] 69.95°±8.84°71.30°±7.07°B evilaqua [8] 68.62°±8.47°64.13°±7.32°T rott [9] 71.7°78.0°t his research 63.4°60.4° Figure 1 Patient's cervical spine x-ray 13 Figure 2 CT scan of the patient's cervical spine