2022, Vol. 26 ›› Issue (33): 5265-5270

Establishment and validation of finite element model of cervical facet joint in children

He Yujie1, Li Pei2, Xue Mingming3, Li Zhijun1, Li Xiaohe1, Wang Xing1, Gao Mingjie1, Wu Chao2, Kang Zhijie4, Zhang Shaojie1, Wang Haiyan1   

Abstract: BACKGROUND: The cervical vertebra in children is not yet mature. The ligaments are relatively relaxed. The articular surface is relatively horizontal. The uncinate vertebra joint begins to develop. Therefore, the superior cervical junction area and the lower cervical vertebra in children are vulnerable to injury. It is of great significance to study the mechanical properties and injury mechanism of children’s neck for its protection and treatment.  
OBJECTIVE: The finite element model of the whole cervical vertebra of a 4-year-old child was established to compare and analyze the maximum stress value of the joint surface of each segment, so as to understand the mechanical change rule under different motion states.
METHODS: The original data of continuous cervical spine tomography images were imported into Mimics 21.0 in DICOM format to reconstruct C0-T1 respectively, imported into 3-Matic to establish a preliminary geometric model of the disc, and then processed with denoising, paving, and smoothing. The improved model was imported into Hypermesh software for mesh division. After attribute assignment, the material was imported into the finite element model displayed in ANSYS 19.2, and the boundary and load conditions were set to observe the range of motion of the joint and the stress and strain values of the joint surface of each segment.  
RESULTS AND CONCLUSION: (1) The maximum range of motion of the facet joint was C4/5 (4.71°, 4.13°, 7.21°, 7.22°) in the forward flexion, backward extension, left flexion, and right flexion, and C2/3 (9.54°, 9.65°) in the axial rotation (left rotation and right rotation). (2) The maximum stress of the disc in the right flexion state was significantly greater than that in the other motion states. The maximum stress of the disc in the forward flexion state was at C5-6 (0.235 MPa) and the maximum stress of the disc in the other states was at C6-7. The maximum stress of the disc at C2-3 segment was smaller than that at   the other segments under the six conditions. (3) Under the same vertebral articular process joint surface, maximum stress under six conditions was greater than articular process on the joint surface, increasing trend with the increase of the operation sequence. The peak was located in the stretched position C6 articular process under the joint surface (1.481 MPa) and the valley value was located in forward flexion joint surface on a C2 (0.005 MPa). (4) In conclusion, the maximum range of motion of the cervical facet joint was located at C2/3, which was negatively correlated with its maximum displacement and maximum stress. Therefore, cervical instability was more common at the upper cervical segment. At the right flexion of the cervical spine, the stress value of the disc at the C6-7 level was the greatest, which was easy to cause cervical disc herniation. The C6/7 facet joint has the largest pulling load no matter what kind of working condition it is in and it is a common site of cervical facet joint induced cervical spondylosis.
Key words: cervical spine, facet joint, preschool child, finite element, motion range, mechanical load, digital model