Clinical Significance And Mechanical Study Of‘Tendon-bone Imbalance’in Intermediate Vertebral Collapse After 2-level ACDF

Objective1.To determine the occurrence of‘tendon-bone imbalance’in intermediate vertebral collapse after 2-level ACDF,and to investigate its clinical significance,mechanism,risk factors.2.To observe the correlation between‘tendon-bone imbalance’in intermediate vertebral collapse and TCM syndrome type after2-level ACDF,and to discuss the significance of TCM intervention in its prevention and treatment.3.To observe the therapeutic effect of stick assisted manipulation on axial pain after 2-level ACDF.4.To clarify the mechanical mechanism of intermediate vertebral collapse after 2-level ACDF.Methods1.Clinical studyA retrospective study was conducted to analyze the patients who underwent 2-level ACDF treatment with 4-screw ZP or CP due to cervical spondylosis in the First Affiliated Hospital of Guangzhou University of Chinese Medicine from March 1,2018 to June 31,2021.Studies were included after inclusion and exclusion criteria.The age,gender,BMI,L1-4 BMD,NDI,JOA,Axial pain VAS score,dysphagia,Traditional Chinese medicine(TCM)syndrome types,the overall physiological curvature of the cervical spine,the physiological curvature of the surgical segment,the incidence of intermediate vertebral body collapse,the interbody fusion,and the occurrence of adjacent segment degeneration were analyzed in the two groups of patients.On this basis,the cases in the ZP group were divided into the collapse group and the non-collapse group for further comparison,and the cases in the collapse group were analyzed one by one to explore the risk factors and mechanisms of the disease.The significance of TCM intervention in the prevention and treatment of intermediate vertebral collapse after 2level ACDF were discussed by combining TCM syndrome type and pathogenesis.The patients with postoperative neck pain were divided into the stick assisted manipulation group and control group according to treatment mode.The VAS scores of axial pain before and after treatment were compared between the two groups.2.Finite element studyA detailed nonlinear three-dimension intact finite element model was developed using computed tomography scan data of the cervical spine(C2-T1)of a male volunteer.The geometry was established by Mimics software and optimized on the Geomagic Studio software,then output in a stereolithography(STL)format and was assembled by the Solidwork software.Hypermesh was used to generate meshes and assign materials,properties,and contact relationships.A three-dimensional finite element(FE)intact cervical model(C2-T1)was constructed and validated.The intact finite element model was then modified to build ACDF models and imitate the situation of endplate injury,establishing two groups of model(ZP、IM-ZP和CP、IM-CP).The physiological compressive load 73.6 N,and moment 2 Nm were applied at the superior of the vertebra C2,and the inferior endplate of the T1 vertebra was constraint for all degrees of freedom.Simulate cervical motion such as flexion,extension,lateral bending and axial rotation and compare degree of motion(ROM),upper and lower endplate stress,fusion fixation device stress,C5 vertebral body stress,intervertebral disc internal pressure(IDP)and the ROM of adjacent segments in models.Results1.Clinical study resultsA total of 57 patients were included in this study,including 27 patients in the ZP group and 30 patients in the CP group.There were no statistically significant differences in age,gender,BMI,L1-4 BMD,NDI,JOA,overall physiological curvature of cervical spine,physiological curvature of surgical segment,and distribution of TCM syndrome types between the two groups.Postoperative NDI scores improved over time in both groups(P<0.001),the NDI score of CP group was significantly improved compared with that of ZP group,and the difference was statistically significant(P=0.008).JOA scores improved over time in both groups(P<0.001),but there was no significant difference in JOA score between the two groups(P=0.314).The overall physiological curvature of the cervical spine and the physiological curvature of the surgical segment were significantly improved in both groups after surgery,but with pass of time,there was a greater trend of loss in the ZP group.The overall physiological curvature loss score of the cervical spine at the last follow-up and the surgical segment curvature loss score of the two groups were significantly higher in the ZP group than in the CP group(P<0.001,P=0.033).At last follow-up,there was no significant difference in the incidence of interbody fusion and adjacent segment degeneration between the two groups.However,the incidence and degree of axial pain were higher in ZP group.During the whole observation period from immediately after operation to the last follow-up,4 cases of intermediate vertebral collapse occurred in the ZP group,while no case of collapse occurred in the CP group,with statistical difference between the groups(P<0.05).In the ZP group,both the collapse group and the non-collapse group obtained satisfactory JOA and NDI scores(P<0.05),and there was no statistical difference between them.The incidence of axial pain(P=0.028)and VAS score(P=0.002)in the collapse group were significantly higher than those in the non-collapse group at the last follow-up.There were significant differences in axial pain distribution between the two groups one month after surgery(P=0.023).In the collapse group,axial pain was distributed in the posterior neck region,while in the non-collapse group,axial pain was distributed in the posterior neck region,shoulder-neck junction region,and scapular region.The distribution of TCM syndrome types between the two groups were significant difference(P=0.046).All cases in collapse group were deficiency of liver and kidney,while deficiency of liver and kidney,Qi stagnation and blood stasis,phlegm and dampness blocking collages were included in non-collapse group.Further deterioration of intermediate vertebral collapse was not observed in all of the 4 cases 6 months after surgery.In postoperative cervical pain cases,the axial pain VAS score of stick assisted manipulation group was significantly better than that of the control group(P<0.05).3.Mechanical research resultsUnder flexion and extension conditions,stress of the lower endplate of C5 is significantly greater than that of C4 in all the four modelsCompared with CP groups,greater range of motion(ROM)of surgical segment,more stress on endplates,fusion fixation device and C5 vertebral body during flexion,extension,lateral bending and axial rotation were observe in ZP groups.No significant difference was found between IM-CP model and CP model in the ROM of surgical segment,stress of endplates,fusion fixation device stress and C5 vertebral body stress,as well as IDP,ROM in the adjacent segments.The stress distribution diagram showed that the stress of the two models was evenly distributed on the plate and screw.Compared with the CP model,endplate stress of the ZP model is significantly higher in the flexion,extension,lateral bending and axial rotation conditions.Compared with ZP model,endplate stress of IM-ZP is significantly increased in the flexion,extension,lateral bending and axial rotation conditions(stress of C4 lower endplate increased by 23.0%,22.0%,6.6%and 10.2%,respectively.Stress of C5 upper endplate increased by 19.0%,11.6%,18.9%,20.7%,respectively.Stress of C5 lower endplate increased by 22.8%,19.1%,17.9%and 6.2%,respectively.Stress of C6 upper endplate increased by 8.4%,12.7%,16.2%and 7.8%,respectively.).The stress distribution diagram showed that the endplate stress of both the ZP model and the IM-ZP model was concentrated in the front 1/3 of the endplate,and the stress at the junction of the endplate screws was the highest.When compared with the ZP model,during flexion,extension,lateral bending and rotation,stress of C4/5 segment screw in the IM-ZP model increased by 41.2%、22.4%、15.1%、19.1%prospectively,while stress of C5/6 segment screw,stress of cage in C4/5,stress of cage in C5/6,stress of C5 vertebra,IDP in C34 segment and IDP in C67 segment increased by(26.9%、13.5%、8.1%、25.9%),(12.8%、15.9%、23.3%、21.1%),(19.1%、11.0%、39.0%、18.7%),(41.6%、58.0%、45.8%、23.7%),(18.7%、22.6%、36.5%、33.1%)and(44.5%、55.1%、31.6%、22.7%),prospectively.Conclusion1.Compare to 2-level ACDF using CP,collapse of the intermediate vertebra is more likely to occur using ZP due to mechanical characteristics.Decreased BMD,intraoperative injury of the anterior edge of endplate,excessive distraction,and preoperative stenosis of the intervertebral space are potential risk factors for intermediate vertebral collapse after 2-level ACDF using ZP.2.Intermediate vertebral collapse affects the efficacy by increasing incidence and severity of axial pain,losing physiological curvature of cervical spine,and increasing the risk of implant-related complications.3.Deficiency of liver and kidney is the main syndrome type of intermediate vertebral collapse.Intermediate vertebral collapse might be treated or prevented by TCM based on tendon-bone balance theory.4.Stick assisted manipulation can achieve better efficacy than traditional manipulation using hand only in treating axial pain after 2-level ACDF.