Finite element analysis of the pathological state of cervical vertebrae after vertebral displacement under the theory of Feng's spinal manipulation

HU Xiangyu; FENG Zihe; MA Weiwang; LIU Hongbo; FENG Wei

doi:10.3969/j.issn.2097-1753.2025.04.013

Abstract：Objective To explore the stress changes in cervical disc structures and balance-related components following vertebral displacement in cervical spondylosis patients,and the potential mechanisms underlying symptom relief after manual reduction.Methods A healthy female volunteer underwent thin-slice computed tomography(CT)scanning of the entire cervical spine.From these CT images,a bone model was extracted,and subsequent modeling of soft tissues culminated in the completion of a cervical spine FEA model.The model's validity was rigorously evaluated through comparison with the literature currently available.With the Z-axis rotational degrees of freedom(DOF)of the upper surfaces of C4,C5,and C6 vertebrae fixed,simulation mimicking changes in spinal mechanical environment after vertebral displacement were observed.Specifically,the lower surface of the C7 vertebral body was constrained,and a 73.6 N follower load was applied to the upper surface of the C3 vertebral body.Under leftward rotation conditions,the peak stress and distribution patterns in zygapophysial joint and intervertebral discs were meticulously analyzed.Results A finite element model of the C3-C7 cervical spine was established,incorporating a total of 20 ligament groups across five types:the anterior longitudinal ligament(ALL),posterior longitudinal ligament(PLL),ligamentum flavum(LF),supraspinous ligament(SL),and interspinous ligament(IL).The vertebral bodies were primarily composed primarily of tetrahedral elements,while the intervertebral discs and facet joints were primarily modeled with hexahedral elements.The entire model consisted of 351 188 nodes and 183 241 elements.The average range of motion of each segment of the model was basically consistent with the results of published research data.When the Z-axis rotational degrees of freedom of the upper surfaces of the C6,C5,and C4 vertebrae were fixed successively,the peak stress of the bilateral facet joints and intervertebral discs changed significantly compared with the untreated group.The peak stress of the bilateral facet joints of C3-C4 in the C5 fixation group decreased slightly compared with the untreated group,while the peak stress of the bilateral facet joints of C4-C5 increased significantly.Under other conditions,compared with the untreated group,the overall stress of the facet joints below the fixed segment decreased compared with the untreated group,while the overall stress above the fixed segment increased.The peak stress and distribution characteristics of the bilateral facet cartilage from C3 to C7 were mainly concentrated on the opposite side of rotation,with the right cartilage of C3-C4 as the stress concentration point.The peak stress and distribution characteristics of the intervertebral discs from C3 to C7 were mainly concentrated on C4-C5,but after fixing the Z-axis degree of freedom of the upper surface of C4,the peak stress of the intervertebral discs became C3-C4.Conclusion The reduction in rotational degrees of freedom caused by vertebral displacement can lead to obstruction to of biomechanical transmission throughout the cervical spine.The range of motion in the segments below the affected vertebra decreases,while the segments above the affected vertebra compensate by increasing their range of motion to accomplish the overall coupled movement of the cervical spine.This compensatory mechanism accelerates the degeneration of the segments above the affected vertebra.