| Objective: Cervical instability was described as the cervical vertebra can not maintain the normal relative position of the functional units of the spine under physiological load,generating abnormal activities and deformation,the spinal cord and irritating the spinal nerve roots were comprised,causing symptoms such as numbness of the limbs and neck discomfort,and may also stimulate sympathetic nerve endings in surrounding tissues cause symptoms of sympathetic disorders such as dizziness,palpitations,eyelids,and tinnitus.Common causes are trauma,degeneration,congenital malformations,and tumors.With the increasing trend of the global population aging,degenerative lower cervical instability has gradually appeared in clinical practice,but its biomechanical principles are still not very clear,and it is important to further clarify its mechanism.The finite element method was first applied to the calculation of the structural strength of aircraft in the field of engineering mechanics.It was first introduced into the field of biomechanics in 1972.With the development of computer hardware,the improvement of finite element analysis software and the rapid advancement of medical imaging technology,the finite element method has been fully utilized in almost all fields of biomechanics.In the past 50 years of development,the finite element model has evolved from a simple two-dimensional model to a complex three-dimensional model,from simple linear parameters to more simulated nonlinear models,from simple bone models to today's Related muscles,ligaments,spinal cords,etc.can be simulated.Compared with traditional experimental models such as corpses and animals,the advantages of finite element analysis are very significant,and their reproducibility is extremely high.It can be repeated on the same model;accurate expression of complex geometric shapes;very convenient modification of attribute parameters,respectively Simulate the physiological and pathological states of a certain structure;in the postprocessing,the displacement,rotation,stress changes and other related data of any point can be accurately and efficiently extracted without destroying the model.The purpose of this study was to reconstruct the lower cervical vertebrae model by finite element method,and to analyze the influence of structural degeneration of ligaments and intervertebral discs on the stability of the lower cervical vertebrae,whether the reduction of intervertebral space would reduce the ability of intervertebral foramen and the spinal canal stenosis associated with the lower cervical vertebrae.The study of unstable spinal cord compression provides a theoretical basis for the prevention of degenerative lower cervical instability and assists in early diagnosis and treatment.Methods: The first part: The established three-dimensional nonlinear finite element model contains a total of 60,435 nodes and 153,155 units,of which 56,950 are hexahedral units(C3D6),95,950 tetrahedral units(C3D4),and 255 truss units(T3D2).Using the same boundary conditions and loads as the in vitro mechanical experiments,the measured ROM is compared with the reports in the literature.The results are basically the same,the data is highly consistent,and the verification model can simulate the movement of the lower cervical structure.The results are accurate and available.In related biomechanical studies.The second part: after the ligament degeneration,the ROM of each segment of the cervical vertebrae increased to different extents,especially in the flexion and tilting(P<0.01),but the ROM change was not obvious when rotating(P>0.05).).The influence of the stress distribution on the endplate,nucleus pulposus and annulus structure: it showed a similar trend to the change of ROM.The nucleus pulposus,the annulus fibrosus and the endplate stress of each segment in the flexion and extension exercises increased to varying degrees(P<0.05),the stress of the nucleus pulposus of each segment increased(P<0.05),while the structural stress did not change during rotation.In the model simulating the third degree of cervical disc degeneration,the curvature of the cervical vertebrae became straight due to the loss of the height of the intervertebral space.After the degeneration of the intervertebral disc,the activity of each segment was gradually decreased with the degeneration and increased(P<0.05).The activity of normal and primary degeneration was basically the same during the extension exercise(P>0.05).At the second stage of degeneration,the activity activity decreased significantly(P<0.05),and the second-level degeneration to the third-level degeneration activity did not change much(P>0.05).The changes in activity under the rotational motion and the lateral bending motion are basically similar,and the ROM is reduced in each level of degeneration(P<0.05),and after the second degree is converted to the third degree of degeneration,that is,the activity of the intervertebral space is reduced.The decline is obvious.The stress distribution of the nucleus pulposus was similar under different movements,and the majority of the differences were significant(P<0.05).The stress was the smallest in normal structure,the stress was the largest in the first stage degeneration,and the stress redistribution occurred.C34 intervertebral disc nucleus Stress concentration.The fiber ring stress did not fluctuate with the degree of degeneration in the rotational motion(P>0.05),but the peak appeared in different segments.In other exercises,the stress decreased with the degree of degeneration(P<0.05)..The endplate stress appeared to increase gradually with the increase of degeneration in the flexion movement(P<0.05),and the peak of C56 segment appeared in the third-stage degeneration in the extensional movement.There was no significant difference in the degeneration stress of other grades.(P>0.05).The degree of degeneration with the increase of the degree of degeneration in the roll and the rotation motion increased(P<0.05),and the stress peak of the rotational motion appeared in the C2-C4 segment.The third part: the loss of intervertebral space will lead to the reduction of the inner diameter of the intervertebral foramen,resulting in the occurrence of intervertebral foramen stenosis In the normal intervertebral space model,the cervical forward flexion can increase the minimum internal diameter of the intervertebral foramen,and the intervertebral foramen decreases during the posterior extension.In the rotational motion,the intervertebral foramen on one side of the rotation axis(clockwise to the right)are reduced,and the other intervertebral foramen is enlarged.A similar situation occurs in the lateral bending motion.On the present side(right side when left tilted),the intervertebral foramen enlarges and the intervertebral foramen of the curved side decreases.In the model of height loss of the intervertebral space,the effect of most exercises on the intervertebral foramen is similar to that in the normal intervertebral space model.The degenerative model(reduced 1/3 and 2/3)showed little change in the area of the intervertebral foramen of the intervertebral foramen in the lateral bending motion,which may be related to the reduction of the intervertebral space and the lower part of the small joint.Health contact,lack of further compression space.The fourth part: by using the soft tissue expansion and the inner growth of the lamina on the posterior surface of the intervertebral disc,the inner diameter of the spinal canal was reduced,and the mild(1MM)and severe(2MM)cervical spinal stenosis models were successfully established.In the anterior and posterior translational and anterior flexion of the severe cervical spinal stenosis group,there is contact between the spinal cord model and the proliferative epiphysis or the intervertebral disc.In similar cervical vertebrae,the spinal cord is compressed and the limbs appear.Neurological symptoms such as numbness and bradykinesia.Results: The first part: The established three-dimensional nonlinear finite element model contains a total of 60,435 nodes and 153,155 units,of which 56,950 are hexahedral units(C3D6),95,950 tetrahedral units(C3D4),and 255 truss units(T3D2).Using the same boundary conditions and loads as the in vitro mechanical experiments,the measured ROM is compared with the reports in the literature.The results are basically the same,the data is highly consistent,and the verification model can simulate the movement of the lower cervical structure.The results are accurate and available.In related biomechanical studies.The second part: after the ligament degeneration,the ROM of each segment of the cervical vertebrae increased to different extents,especially in the flexion and tilting(P<0.01),but the ROM change was not obvious when rotating(P>0.05).).The influence of the stress distribution on the endplate,nucleus pulposus and annulus structure: it showed a similar trend to the change of ROM.The nucleus pulposus,the annulus fibrosus and the endplate stress of each segment in the flexion and extension exercises increased to varying degrees(P<0.05),the stress of the nucleus pulposus of each segment increased(P<0.05),while the structural stress did not change during rotation.In the model simulating the third degree of cervical disc degeneration,the curvature of the cervical vertebrae became straight due to the loss of the height of the intervertebral space.After the degeneration of the intervertebral disc,the activity of each segment was gradually decreased with the degeneration and increased(P<0.05).The activity of normal and primary degeneration was basically the same during the extension exercise(P>0.05).At the second stage of degeneration,the activity activity decreased significantly(P<0.05),and the second-level degeneration to the third-level degeneration activity did not change much(P>0.05).The changes in activity under the rotational motion and the lateral bending motion are basically similar,and the ROM is reduced in each level of degeneration(P<0.05),and after the second degree is converted to the third degree of degeneration,that is,the activity of the intervertebral space is reduced.The decline is obvious.The stress distribution of the nucleus pulposus was similar under different movements,and the majority of the differences were significant(P<0.05).The stress was the smallest in normal structure,the stress was the largest in the first stage degeneration,and the stress redistribution occurred.C34 intervertebral disc nucleus Stress concentration.The fiber ring stress did not fluctuate with the degree of degeneration in the rotational motion(P>0.05),but the peak appeared in different segments.In other exercises,the stress decreased with the degree of degeneration(P<0.05)..The endplate stress appeared to increase gradually with the increase of degeneration in the flexion movement(P<0.05),and the peak of C56 segment appeared in the third-stage degeneration in the extensional movement.There was no significant difference in the degeneration stress of other grades.(P>0.05).The degree of degeneration with the increase of the degree of degeneration in the roll and the rotation motion increased(P<0.05),and the stress peak of the rotational motion appeared in the C2-C4 segment.The third part: the loss of intervertebral space will lead to the reduction of the inner diameter of the intervertebral foramen,resulting in the occurrence of intervertebral foramen stenosis In the normal intervertebral space model,the cervical forward flexion can increase the minimum internal diameter of the intervertebral foramen,and the intervertebral foramen decreases during the posterior extension.In the rotational motion,the intervertebral foramen on one side of the rotation axis(clockwise to the right)are reduced,and the other intervertebral foramen is enlarged.A similar situation occurs in the lateral bending motion.On the present side(right side when left tilted),the intervertebral foramen enlarges and the intervertebral foramen of the curved side decreases.In the model of height loss of the intervertebral space,the effect of most exercises on the intervertebral foramen is similar to that in the normal intervertebral space model.The degenerative model(reduced 1/3 and 2/3)showed little change in the area of the intervertebral foramen of the intervertebral foramen in the lateral bending motion,which may be related to the reduction of the intervertebral space and the lower part of the small joint.Health contact,lack of further compression space.The fourth part: by using the soft tissue expansion and the inner growth of the lamina on the posterior surface of the intervertebral disc,the inner diameter of the spinal canal was reduced,and the mild(1MM)and severe(2MM)cervical spinal stenosis models were successfully established.In the anterior and posterior translational and anterior flexion of the severe cervical spinal stenosis group,there is contact between the spinal cord model and the proliferative epiphysis or the intervertebral disc.In similar cervical vertebrae,the spinal cord is compressed and the limbs appear.Neurological symptoms such as numbness and bradykinesia.Conclutions:(1)This study successfully established a three-dimensional nonlinear finite element model by CT scan data,the mesh is detailed,the material properties are real and reliable,and the validated model can be applied to cervical biomechanics research.(2)The decrease in intervertebral disc height caused by degeneration of the intervertebral disc can directly lead to changes in cervical curvature.In daily life,the neck should be prevented from excessive flexion for a long time.In the anterior cervical surgery,the height of the inner plant/bone graft should be properly selected,and the normal intervertebral space height should be restored as much as possible to maintain normal physiological curvature.Degenerative changes of the lower cervical spine are a very complicated process.Changes in each structure promote or cancel each other out.The strength of a certain structure needs to be increased by other structures to maintain the stability of the cervical spine.(3)Maintaining the height of the intervertebral space is important for maintaining the patency of the intervertebral nerve root canal and preventing cervical spondylotic radiculopathy.In the anterior cervical discectomy and bone graft fusion,the intervertebral foramen should be thoroughly and fully decompressed.Pay attention to choose the appropriate Cage model,properly support the high intervertebral space,enlarge the nerve root canal area,and provide sufficient passage space for the cervical nerve root to prevent the nerve root from being compressed again after the segment continues to degenerate.(4)Cervical spinal stenosis can aggravate excessive hyperactivity of the intervertebral space when the lower cervical spine is unstable.For the spinal cord compression stimulation,spinal cord compression can occur when the small slip and rotation occur,and the dynamic pressure should be vigilant in clinical practice.Dynamic MRI can assist in the diagnosis and treatment of such diseases. |
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