Xin-Yi Cai1, Dacheng Sang2, Chen-Xi Yuchi3, Wei Cui4, Chunqiu Zhang5, Cheng-Fei Du6, Baoge Liu7. 1. Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control, School of Mechanical Engineering, Tianjin University of Technology, Tianjin, 300384, China; National Demonstration Center for Experimental Mechanical and Electrical Engineering Education, Tianjin University of Technology, Tianjin, 300384, China. Electronic address: CXY1122@hotmail.com. 2. Department of Orthopaedic Surgery, Beijing Tiantan Hospital, Capital Medical University, No.119, South 4th Ring West Road, Fengtai District, Beijing, 100070, China; China National Clinical Research Center for Neurological Diseases, No.119, South 4th Ring West Road, Fengtai District, Beijing, 100070, China. Electronic address: 1204135308@qq.com. 3. Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control, School of Mechanical Engineering, Tianjin University of Technology, Tianjin, 300384, China; National Demonstration Center for Experimental Mechanical and Electrical Engineering Education, Tianjin University of Technology, Tianjin, 300384, China. Electronic address: 1004458870@qq.com. 4. Department of Orthopaedic Surgery, Beijing Tiantan Hospital, Capital Medical University, No.119, South 4th Ring West Road, Fengtai District, Beijing, 100070, China; China National Clinical Research Center for Neurological Diseases, No.119, South 4th Ring West Road, Fengtai District, Beijing, 100070, China. Electronic address: cuicui0903@163.com. 5. Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control, School of Mechanical Engineering, Tianjin University of Technology, Tianjin, 300384, China; National Demonstration Center for Experimental Mechanical and Electrical Engineering Education, Tianjin University of Technology, Tianjin, 300384, China. Electronic address: zcqarticle@163.com. 6. Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control, School of Mechanical Engineering, Tianjin University of Technology, Tianjin, 300384, China; National Demonstration Center for Experimental Mechanical and Electrical Engineering Education, Tianjin University of Technology, Tianjin, 300384, China. Electronic address: ddccffb31@hotmail.com. 7. Department of Orthopaedic Surgery, Beijing Tiantan Hospital, Capital Medical University, No.119, South 4th Ring West Road, Fengtai District, Beijing, 100070, China; China National Clinical Research Center for Neurological Diseases, No.119, South 4th Ring West Road, Fengtai District, Beijing, 100070, China. Electronic address: baogeliu@hotmail.com.
Abstract
BACKGROUND: Understanding the biomechanical effects of cervical disc degeneration (CDD) on the cervical spine is fundamental for understanding the mechanisms of spinal disorders and improving clinical treatment. While the biomechanical effects of CDD on segmental flexibility and the posterior facets have been reported, a clear understanding of the effect of the motion loading method on facet joint forces after CDD is still lacking. Therefore, the objective of this study was to determine the effect of the motion loading method on facet joint forces after CDD. METHODS: A three-dimensional nonlinear finite element (FE) model of the cervical spine (C3-C7) was developed and validated to represent normal conditions. This normal model was modified to create six degenerative models simulating mild, moderate, and severe grades of disc degeneration at C5-C6. While under a follower compressive preload (73.6 N), a 1-Nm moment was applied to all models to determine range of motion (ROM). A displacement load was applied to all degenerative models under the same follower load, making the C5-C6 degeneration segment motion same to the ROM of C5-C6 in normal model, and facet joint forces were computed. RESULTS: Compared with the normal model, ROM of the C5-C6 degenerative segments dramatically declined in all postures with increasing degenerative pathologies in the disc. The ROM in the adjacent normal segments of the degenerative segments also declined, with the exception of C4-C5 during extension. Under a 1-Nm moment load, there were not obvious changes in facet joint forces in the C5-C6 degenerative segment with increasing grades of degeneration, but facet joint forces in the adjacent normal segments did increase. Under a displacement load, the facet joint forces of the C5-C6 degenerative segment increased with increasing grades of degeneration. CONCLUSIONS: Facet joint forces were positively correlated with the ROM of the degenerative segment, demonstrating that the motion loading method had a significant effect on facet joint forces after CDD. Loading conditions must be strictly controlled in future finite element analysis studies to improve the comparability between models built by different units.
BACKGROUND: Understanding the biomechanical effects of cervical disc degeneration (CDD) on the cervical spine is fundamental for understanding the mechanisms of spinal disorders and improving clinical treatment. While the biomechanical effects of CDD on segmental flexibility and the posterior facets have been reported, a clear understanding of the effect of the motion loading method on facet joint forces after CDD is still lacking. Therefore, the objective of this study was to determine the effect of the motion loading method on facet joint forces after CDD. METHODS: A three-dimensional nonlinear finite element (FE) model of the cervical spine (C3-C7) was developed and validated to represent normal conditions. This normal model was modified to create six degenerative models simulating mild, moderate, and severe grades of disc degeneration at C5-C6. While under a follower compressive preload (73.6 N), a 1-Nm moment was applied to all models to determine range of motion (ROM). A displacement load was applied to all degenerative models under the same follower load, making the C5-C6 degeneration segment motion same to the ROM of C5-C6 in normal model, and facet joint forces were computed. RESULTS: Compared with the normal model, ROM of the C5-C6 degenerative segments dramatically declined in all postures with increasing degenerative pathologies in the disc. The ROM in the adjacent normal segments of the degenerative segments also declined, with the exception of C4-C5 during extension. Under a 1-Nm moment load, there were not obvious changes in facet joint forces in the C5-C6 degenerative segment with increasing grades of degeneration, but facet joint forces in the adjacent normal segments did increase. Under a displacement load, the facet joint forces of the C5-C6 degenerative segment increased with increasing grades of degeneration. CONCLUSIONS: Facet joint forces were positively correlated with the ROM of the degenerative segment, demonstrating that the motion loading method had a significant effect on facet joint forces after CDD. Loading conditions must be strictly controlled in future finite element analysis studies to improve the comparability between models built by different units.