Establishment and validation of a finite element model of sacral lumbarization in adolescents

Wu Xuehai; Wang Xing; Zhang Shaojie; Xu Xuebin; Shi Jun; Wang Tieying; Li Zhijun

Abstract：BACKGROUND: Lumbar sacralization will cause changes in the vertebral body segments, resulting in low back pain during exercise. Epidemiological studies showed that the incidence of lumbar sacralization in adolescents is increasing year by year. OBJECTIVE: To establish a three-dimensional finite element model of adolescent patients with lumbar sacral vertebrae, and to analyze the mechanical properties and stress-strain rules of lumbar vertebrae under simulated normal exercise conditions, so as to provide mechanical basis for the treatment of low back pain caused by sacral lumbarization in clinic. METHODS: The CT images of a 16-year-old male teenager with sacral lumbarization were selected, and the three-dimensional model of lumbar data was established by mimics16.0, and the three-dimensional digital medical modeling method was introduced into Geomagic Studio and ANASYS WorkBench software to establish the finite element model of the lower lumbar and sacral segments of the intervertebral disc. The biomechanical test of the model was carried out by applying the moment of 2 N?mm to simulate the movement of flexion, extension, left bending and right bending after loading normal human body load, and the mechanical changes of displaced vertebrae under various working conditions were analyzed to explore the mechanical characteristics of lumbar sacral vertebrae in adolescents. This trial was approved by the Ethics Committee of Inner Mongolia Medical University (approval No. YKD2018015) on March 5, 2018. RESULTS AND CONCLUSION: During extension and flexion, the stress of L5 and S1 pedicles was significantly greater than that of scoliosis. The direction of stress change of the migration S1 pedicle was the same as that of normal adult L5 pedicle isthmus. In juvenile patients with sacral lumbarization, during lumbar spine movement, the stress on the S1 pedicle isthmus was significantly greater than that on the L5 pedicle isthmus, and the facet joints and intervertebral discs bore greater stress. It is concluded that for adolescents with complete sacral lumbarization, as the stress on the transitional vertebrae increases during lumbar activities, it is more likely to cause fatigue fractures and isthmic fissures, while the facet joints and intervertebral discs are more stressed, making them prone to regression change.