BACKGROUND: Inherent modal analysis and harmonic response analysis on the human normal lumbosacral vertebraehave been reported, but there is a lack of comparative research on their modal analysis results before and after pediclescrew fixation.OBJECTIVE: To explore the dynamic characteristics of human lumbosacral vertebrae using three-dimensional finiteelement method.METHODS: Finite element model of lumbosacral vertebrae (L1-S1) before and after pedicle screw fixation was developedand validated based on CT images, and the modal analysis and harmonic response analysis were then conducted.RESULTS AND CONCLUSION: (1) Representative nodes were selected at the spinous process segments of L1, L3 andL5, and numbered as A, B, and C, respectively. (2) The maximum displacement of each node in Y and Z directions oflumbosacral vertebral model after internal fixation was significantly decreased compared with those of the normallumbosacral vertebral model, suggesting that screw fixation system plays a protective role in lumbosacral vertebrae, andreduces its amplitude under external load, thus diminishing its sensitivity to external load. (3) The lumbosacral vertebralmodal analysis can provide basis for further study on dynamic analysis, and the parameters such as natural frequency,modal shape and vibration amplitude of the lumbar spine have been determined.

Objective To establish the three-dimensional (3D) finite element (FE) model of thoracolumbosacral T1-S spine based on the computed tomography (CT) images of patients with scoliosis and study its dynamic characteristics. Methods The established scoliotic model was validated by axial compression and shear loading, and the predicted responses were in good agreement with the experimental data. The modal and harmonic analyses were performed using the ABAQUS software, and during the harmonic analysis, the dynamic response of the model was collected at frequencies 5 Hz and 10 Hz. Results From the modal analysis, the first fourth-order modal was extracted. The first- and second-order resonant frequencies of the model were 1.097 Hz and 1.384 Hz, respectively, and the vibration mode was longitudinal bending and lateral bending, respectively. The distribution of the second- and third-order modal resonant frequencies were 5.688 Hz and 28.090 Hz, and the vibration mode was vertical vibration and twisting around the long axis, respectively. The peak amplitude in the harmonic analysis appeared near the modal frequencies, and the average amplitude of vertebral body of the lateral convex segment was larger than that of other segments of the scoliotic spine. Under the vibration frequencies of 5 Hz and 10 Hz, the stress inhomogeneously concentrated on the concave and convex sides of the segments of the vertebral deformity as well as on the intervertebral disc. Conclusions The segments of the spinal deformity in patients with scoliosis were the weak links of their spines and more vulnerable to damage in a vibrating environment. Patients with scoliosis should avoid a vibrating environment, particularly in a sensitive frequency range. The research outcomes provide methodological assistance and mechanical analysis references for the protection, rehabilitation treatment, and clinical pathological studies of patients with scoliosis.