Liang Wang1, Bangke Zhang1, Shuo Chen2, Xuhua Lu3, Zhi-Yong Li4, Qunfeng Guo1. 1. Department of Orthopaedics, Changzheng Hospital Affiliated to the Second Military Medical University, Shanghai, China. 2. Biomechanics Laboratory, School of Biological Science and Medical Engineering, Southeast University, Nanjing, China. 3. Department of Orthopaedics, Changzheng Hospital Affiliated to the Second Military Medical University, Shanghai, China. Electronic address: xuhualu@hotmail.com. 4. Biomechanics Laboratory, School of Biological Science and Medical Engineering, Southeast University, Nanjing, China; Science and Engineering Faculty, School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, Australia. Electronic address: zylicam@gmail.com.
Abstract
OBJECTIVE: To develop modified finite element models to simulate degenerative lumbar scoliosis (DLS) based on the normal lumbar spine model and to investigate the facet joint force of the DLS. METHODS: A 3-dimensional finite element model of a normal lumbar spine was modified to simulate 3 different Cobb angles conditions (12.3°, 22.2°, and 31.8°). The stresses on the facet joint were calculated on both sides (right and left) of the each vertebra. Changes of stress and asymmetry in contact forces between facet joints in the development of DLS were quantitatively analyzed to better understand the development of DLS and the biomechanical forming mechanism. RESULTS: The results show that asymmetric responses of the facet joint forces exist in various postures and that such effect is amplified with larger curve. When the Cobb angle was smaller, the convex side of the facet joints suffered larger force. When the Cobb angle was larger than 20°, the concave side of the facet joints suffered larger force. In the axial-rotation cases, the facet joint compression is less often located on the ipsilateral side than the contralateral side at the same level. CONCLUSIONS: With the asymmetric loading, facet joints compressive deformation appears on the concave side, and it decreases in the effect of the facet joints to limit the vertebral rotation and listhesis. Asymmetric loading on facet joint contact forces accelerates asymmetry in the lumbar spine.
OBJECTIVE: To develop modified finite element models to simulate degenerative lumbar scoliosis (DLS) based on the normal lumbar spine model and to investigate the facet joint force of the DLS. METHODS: A 3-dimensional finite element model of a normal lumbar spine was modified to simulate 3 different Cobb angles conditions (12.3°, 22.2°, and 31.8°). The stresses on the facet joint were calculated on both sides (right and left) of the each vertebra. Changes of stress and asymmetry in contact forces between facet joints in the development of DLS were quantitatively analyzed to better understand the development of DLS and the biomechanical forming mechanism. RESULTS: The results show that asymmetric responses of the facet joint forces exist in various postures and that such effect is amplified with larger curve. When the Cobb angle was smaller, the convex side of the facet joints suffered larger force. When the Cobb angle was larger than 20°, the concave side of the facet joints suffered larger force. In the axial-rotation cases, the facet joint compression is less often located on the ipsilateral side than the contralateral side at the same level. CONCLUSIONS: With the asymmetric loading, facet joints compressive deformation appears on the concave side, and it decreases in the effect of the facet joints to limit the vertebral rotation and listhesis. Asymmetric loading on facet joint contact forces accelerates asymmetry in the lumbar spine.