Abstract: BACKGROUND: Adolescent idiopathic scoliosis is a common spinal deformity that seriously affects the physical and mental health of patients. Modal analysis will focus on analyzing the natural vibration characteristics of the thoracic spine and its stability and response under the influence of external vibration. This analysis is expected to not only enhance the understanding of the thoracic curvature of adolescent idiopathic scoliosis, but also provide new perspectives and methods for developing new treatment strategies, designing personalized braces, and evaluating surgical outcomes.
OBJECTIVE: To create a three-dimensional finite element model to evaluate the response modes of the entire thoracic spine and intervertebral discs in adolescent idiopathic scoliosis patients at different vibration frequencies, and determine the potential frequency range of injury risk.
METHODS: This study was jointly conducted at the Sixth Affiliated Hospital of Xinjiang Medical University and the School of Mechanical Engineering at the Boda Campus of Xinjiang University from June 2023 to June 2024. The research subject was a patient with severe spinal and thoracic curvature. CT images were obtained using Siemens dual source spiral CT scanning, and a fine T1-T12 three-dimensional finite element model was established using software such as Mimics, Geomagic Studio, Solidworks, and Hypermesh. Abaqus software was used to perform modal analysis on the model and obtain the maximum amplitude and corresponding vibration modes of the first 12 modes of the entire thoracic spine and intervertebral disc. 
RESULTS AND CONCLUSION: (1) The modal analysis results showed that the entire thoracic vertebrae and intervertebral discs mainly bent and twisted around the X and Y axes in the lower order modes, while increasing rotation around the Z axis in the higher order modes. (2) The T1-T3 and T6-T8 segments showed the most significant deformation and higher load burden, indicating that these regions played a crucial role in the development of scoliosis. (3) When the natural frequency was concentrated between 98.832 to 121.97 cycles/s for a long time, the vibration displacement of the entire thoracic vertebrae and intervertebral discs was large, which might lead to spinal injury. (4) Through finite element modal analysis, this study provides a scientific basis for understanding the response of the entire thoracic spine and intervertebral discs in adolescent idiopathic scoliosis patients under various vibration frequencies, thereby offering crucial insights into clinical treatment, prevention, and particularly, vibration-related protective strategies. Furthermore, by identifying the potential frequency range of injury risk, this study provides an important basis for developing vibration protection measures and optimizing spinal care strategies for adolescent idiopathic scoliosis patients.

Key words: adolescent idiopathic scoliosis, finite element modal analysis, three-dimensional finite element model, biomechanical property, injury risk