2023, Vol. 27 ›› Issue (9): 1365-1370

Finite element analysis of transarticular screw fixation of adolescent thoracic vertebra

He Yujie1, Kang Zhijie2, Xue Mingming3, Jin Feng4, Li Zhijun1, Wang Xing1, Xu Yangyang5, Gao Mingjie1, Li Jiawei2, Li Xiaohe1, Wang Haiyan1   

Abstract: BACKGROUND: Facet screw fixation is currently accepted as an internal fixation method. It has been extensively studied and applied in the cervical spine and lumbar spine.
OBJECTIVE: To quantitatively analyze and compare biomechanical properties of transarticular screw fixation and traditional pedicle screw fixation in adolescents using finite element method to explore the feasibility of the former in thoracic internal fixation.
METHODS: The finite element models of total thoracic vertebral pedicle screw fixation (Model A) and transarticular screw fixation (Model B) were established in 14-year-old adolescents. The original data of continuous scan thoracic vertebral tomography images were imported into Mimics 21.0 in DICOM format. T1-T12 were reconstructed and then imported into 3-Matic to establish preliminary geometric models of discs, facet joints, screws and titanium rods, and then processed with denoising, surfacing, smoothing and so on. The models were imported into Hypermesh software to carry on the grid. After attribute assignment, materials were imported into Ansys 19.2 to show the finite element model. Boundary and load condition were set. The motion range and stress of pedicles, intervertebral discs, screws, and titanium rods were observed, and whether the two had the same force and biomechanical stability were analyzed.
RESULTS AND CONCLUSION: (1) The range of motion of facet joints in all segments of pedicle screws was greater than that of facet screws in all six working conditions (flexion, extension, left rotation, right rotation, left flexion, right flexion). The maximum motion was located at T11/12 segment in the left flexion state (Model A: 0.691°; Model B: 0.563°). (2) There was no significant difference in the stress value of the pedicle between the two groups in flexion, extension, lateral flexion and left rotation (P > 0.05). In right-rotation state, the segments with significant differences (P < 0.05) were located at T3 and T6-T9, respectively, and the stress values of the model in Model A were higher than those in Model B. (3) There was no significant difference in the stress value of the superior articular process between Model A and B in flexion, extension, and lateral flexion motion (P > 0.05). In left-rotation and right-rotation states, the segments with significant differences (P < 0.05) were located at T10 and T8, respectively, and the stress values of the superior facet in Model B were higher than those in Model A. (4) The average stress value of T1-2 intervertebral disc in Model B was greater than that in Model A only in flexion forward, flexion right and rotation right, but was smaller than that in Model A under other conditions. In the overall stress cloud of titanium screw and rod, the average stress value of Model A was greater than that in Model B. (5) It is concluded that the biomechanical properties of small articular screws are similar to those of traditional pedicle screws, and posterior transarticular screw fixation in the thoracic spine can be used as an alternative fixation method.
Key words: thoracic, facet screw, pedicle, teenager, finite element analysis