The Exploration Of The Relationship Between The Cervical Facet Tropism And Cervical Disc Herniation Based On Imaging And Finite Element Analysis

Part 1 The exploration of the relationship between the cervical facet tropism and cervical disc herniation based on imaging BackgroundMany studies have demonstrated the association between facet tropism and disc herniation in the lumbar spine.Some of them have shown a greater risk of lumbar disc herniation on the side of the more coronal facet joint interface.However,little is understood about the association of facet tropism with cervical disc herniation.ObjectiveThe purpose of our present study is to explore the relationship between the cervical facet tropism and cervical disc herniation.MethodsNinety-six patients with single-level cervical disc herniation(20 cases of C4-C5,50 cases of C5-C6,and 26 cases of C6-C7)at the First Affiliated Hospital of Guangzhou University of Chinese Medicine from June 2015 to December 2020 were included in the CDH group of this study.Another fifty age-matched and gender-matched healthy participants who accepted physical examinations were enrolled as the control group.They all underwent a CT scan of the cervical spine.The sagittal angles of facet joints on both sides of the cervical spine were measured and recorded on CT images.The data of the two groups were collected and counted.The CDH group mainly included age,gender,responsible segment of disc herniation,location distribution of disc herniation and both sides of sagittal angle of cervical facet joint.The control group mainly included age,gender,and both sides of sagittal angle of cervical facet joints at C4-5,C5-6 or C6-7.Results(1)Compared with the control group,the number of cases of facet tropism in the C4-5,C5-6,C6-7 segments in the CDH group was significantly more(p=0.021,p=0.001,p=0.015,respectively).Moreover,the difference of left and right facet joint angles was significantly larger than that of the corresponding segments in the control group(p=0.001,p=0.002,p=0.028,respectively).(2)In CDH group,the facet joint angle on the herniated side was significantly larger than that on the non-herniated side(p=0.000,p=0.000,p=0.037,respectively).ConclusionsCervical facet tropism is associated with cervical disc herniation,and the side with the larger facet joint angle is at higher risk of herniation.Part 2 The exploration of the influence of cervical facet tropism on the stress of intervertebral disc annulus based on finite element analysisBackgroundOur previous clinical studies showed that facet tropism was associated with cervical disc herniation and larger facet angle with respect to the sagittal plane were more prone to disc herniation,no biomechanical tests to explain this conclusion.Therefore,we use finite element analysis to investigate the biomechanical association between facet tropism and cervical disc herniation and the relationship between the facet orientation and the herniated side of cervical disc herniation.ObjectiveThe purpose of our present study is to investigate the biomechanical impact of the facet tropism on the stress of annulus fibers of disc and the relationship between the facet orientation and the herniated side of cervical disc herniation.MethodsThe CT scans of a 25 year-old male volunteer was used to construct the finite element model.Firstly,a cervical model from C3 to C7 was constructed.The model was verified using the data from previously published study.Secondly,the facet orientations at the C5-C6 level was altered to simulate the facet tropism with respect to the sagittal plane.Five models,F70,F80,F90,F100,F110 were simulated with different facet joint orientations(70°,80°,90°,100°,110° facet joint angle at the left side respectively and 90°facet joint angle at the right side)at C5-6 facet joints(F90 is a symmetric model).In each model,the stress of annulus fiber and facet joint were investigated under four pure moments and combined loading.Results(1)Five models did not differ in the annulus fiber stress under flexion,extension,lateral bending,left rotation and flexion combined with left rotation moment.But under right rotation and flexion combined with right rotation moment,the larger the facet joint angle with respect to the sagittal plane,the greater the pressure in the annulus fiber.Compared with F90 model,the annulus fiber stress of F70,F80,F100,F110 model increased by-24.86%,-11.41%,16.65%,35.16% under right axial rotation and-9.99%,-6.63%,19.47%,54.39% under flexion combined with right axial rotation moment.It is worth noting that the maximum stress of annular fibers is concentrated on the left posterolateral side under flexion combined with right rotation moment and on the right posterolateral side under flexion combined with left rotation moment.(2)Compare the maximum stress of the annulus fibers between in flexion combined with left rotation and flexion combined with right rotation in each model,we found that in F90 model,there was little difference in the maximum stress between the left posterolateral and right posterolateral annular fibers during such movement,while the difference was obvious in F80 and F100 model,and the difference was more obvious in F70 and F110 model.In the F70 and F80 models,the maximum stress of right posterolateral annulus fibers under flexion combined with left rotation moment was larger than the left posterolateral annulus fibers under flexion combined with right rotation moment,and in the F100 and F110 models,the maximum stress of left posterolateral annulus fibers was larger than the maximum stress of right posterolateral annulus fibers.(3)These is almost no pressure on the left side of facet joint under the flexion,left rotation,and flexion combined with left rotation moment.The five models just had little effect on the left side of facet joint stress under extention and lateral bending moment,but the F90 model was subjected to the least pressure compared to the other models under the right rotation and flexion combined with right rotation moment.In addition,there is almost no pressure on the right side of facet joint under the flexion,right rotation,and flexion combined with right rotation moment.The five models just had little effect on the right side of facet joint stress under extention,lateral bending,the left rotation and flexion combined with left rotation moment.ConclusionsCompared with the left and right facet joints,the bigger the facet joint angle is,the larger the stress on the annulus is under the contralateral rotation or the contralateral rotation combined with flexion,and the maximum stress is concentrated on the posterolateral disc of the ipsilateral facet joint.Cervical facet tropism is prone to uneven stress of intervertebral disc annulus,which increases the risk of intervertebral disc injury.