A three-dimensional finite element model of lumbar sacral vertebrae was established In this study, a three-dimensional finite element model of lumbar sacral vertebrae in adolescents was established based on the data of patients with lumbar sacral vertebrae, including 22 815 elements and 12 785 nodes (Table 3). The model is highly simulated, the geometric structure is good, the appearance of the model is close to the structure of sacral lumbar data, and has a high degree of reduction (Table 3 and Figure 6)."

"

Stress analysis of lumbar vertebrae of sacral vertebrae under different working conditions in three-dimensional finite element model of adolescents When the torque of 2 N·mm was applied to the lumbar vertebra finite element model of sacral vertebrae, the stresses of L5 and S1 under lumbar vertebrae of sacral vertebrae were as follows: during flexion, the stress was mainly concentrated in the facet joint of S1Unix 2, followed by the posterior structure of each vertebra. During the extension, the stress was mainly concentrated in the S1ax 2 facet joint, and decreased in turn from S1 to upward, which was basically consistent with the flexion movement. In the left and right side flexion, the stress is mainly concentrated in the S1hip 2 facet joint, followed by the superior articular process of S1, and decreases upward from S1. For the symmetry of human body development, the stress and strain of the model under the right bending condition is the same as that of the left bending. In the axial torsion of the left and right sides, the stress is greater in the anterior part of the C2-3 vertebral body, and the stress is also obvious in the facet joint and pedicle of the opposite side of the vertebral body. For L5 and S1 vertebrae, the maximum stress appeared in the inferior articular process of the vertebrae under flexion and extension, followed by the isthmus of the pedicle of the vertebrae, and in the condition of left and right lateral bending, the maximum stress appeared in the inferior articular process of the vertebrae, followed by the superior articular process of the vertebrae, and then in the isthmus of the pedicle of the vertebrae (Figure 7)."

Strain and displacement analysis of lumbar vertebrae of sacral vertebrae under different working conditions in adolescents three-dimensional finite element model In the stress analysis of the model, the maximum strain was located in the intervertebral disc tissue under different working conditions, and the strain law was that S1 decreased upward, and the maximum displacement was located at the anterior upper edge of L4 during flexion. Under the left bending condition, the maximum strain of the model was S1Scan2, and there was little difference in stress between L4-5 and L5/S1 (Figure 7). To analyze the displacement changes of the model under different working conditions, during flexion and extension, the maximum displacement is located at the upper edge of L4, and the displacement decreases successively from L4 to the sacrum. Under the condition of left and right side bending, the maximum displacement is located at the front and upper edge of L4, and the displacement decreases successively from L4 to downward (Figure 8)."