ABSTRACT
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.
ABSTRACT
Objective To study the correlation between the deformation and displacement trend of the lumbosacral vertebra (L1-S1) for two typical scoliosis spines under vertical loads,so as to provide the mechanical basis of treatment and prevention of scoliosis in clinic.Methods The X-ray computed tomography (CT) images of two typical scoliosis spines (Lenke-4AN type and Lenke-5CN type) were converted into 3D models,and their finite element models were then established and verified.The internal stress distribution and displacement variation of the models were calculated by the finite element software;the correlation between the lumbosacral vertebral structure and displacement of the spine was analyzed.Results Under the same boundary conditions and load cases,the stress and displacement for two kinds of lumbosacral vertebral models showed different trends.Due to its leftleaning and forward convex bending deformation as well as the relatively large lordosis angle (60°) and smaller left-leaning angle (17.37°),the Lenke-4AN type lumbosacral spine produced slightly small forward convex displacement (8.18 mm) and relatively large left-leaning displacement (0.97 mm).The Lenke-5CN type lumbosacral spine showed left-leaning and forward convex bending deformation as well,with relatively large lordosis angle(59°) and left-leaning angle (26.97°),so it produced more severe left-leaning displacement (20.65 mm) andforward convex displacement (9.22 mm).Conclusions The deformation trend of lumbosacral vertebra is closelyrelated to its structural characteristics,and different scoliosis lumbosacral vertebral structures will cause the corre-sponding deformation trend.The research findings are important for the prevention and treatment of scoliosis.
ABSTRACT
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.