Radiographic And MRI Features Of Cervical Alignment And Its Predictors In Adolescent Idiopathic Scoliosis

Adolescent idiopathic scoliosis(AIS)is essentially three-dimensional deformity of the spine.While the coronal plane is the diagnostic criteria of AIS,sagittal curvature change is an important character and a complex issue as well.The structure and function of the cervical region make it suspectable to the disorders of thoracic and lumbar alignment,which inevitably lead to a much higher incidence of abnormal cervical curvature in AIS patients than that in asymptomatic peer.Long-term abnormal cervical curvature is closely related to dysfunction of cervical dynamics which can increase the longitudinal cord tension,reduce blood supply and induce the cervical spondylotic myelopathy.In hence,the cervical curvature of AIS patients has been received increasing concern.Although its clinical significance had been questioned by the showing of many studies reported no relationship between cervical curvature and neck pain,abnormal cervical curvature is still an unignored disorder in AIS patient for the reason of causing severe cervical spine disorders in his adulthood.At present,the researches of cervical curvature in AIS were mainly focused on X-ray parameters,cervical disc degeneration in MRI got little attention.The relationship between cervical curvature and cervical disc degeneration in AIS patients was still not clear.Furthermore,several studies were conducted attempting to illustrate the compensatory mechanism between cervical sagittal alignment and other sagittal parameters in AIS,nevertheless,the results remained controversial.In this paper,to tackle the problems above,we firstly offered a more reliable description of the characteristic of cervical curvature in AIS patients by grouping according to the cervical morphology and analyzed its associated coronal and sagittal spinal-pelvic parameters in AIS patients.Then we assessed the situation of cervical disc degeneration in AIS patients and analyzed its correlation with cervical curvature.We found that the connection between the two aspects above could be a vicious cycle that promotes each other and both sides are mutually causative.Finally,we discovered the importance of postoperative thoracic alignment correlated with cervical alignment by analyzing the correlations of preoperative,postoperative and follow-up CLA and corresponding other sagittal parameters,respectively.The correction of thoracic curvature by surgery was helped to the improvement of postoperative and follow-up cervical kyphosis.Our study explored the compensatory mechanism of cervical alignment based on the feature of preoperative and postoperative sagittal parameters of AIS patients and identified the parameters that could forecast the cervical sagittal alignment after long-term follow-up.These results could provide specific guidelines for developing individual surgical plans.The whole study was divided into three parts:Part Ⅰ: Radiographic feature and parameter analysis of cervical curvature in adolescent idiopathic scoliosisObjective.The purpose of this study was to evaluate the radiographic features of cervical curvature in AIS patients and its relevance with other spinal-pelvic parameters.Method.A retrospective study was performed on 92 AIS patients treated by posterior spinal fusion in Xijing Hospital of the Air Force Medical University between July 2012 and November 2016.The patients were classified according to the Lenke curve type,Lenke lumbar spine modifier and Lenke sagittal thoracic modifier,and divided into normal cervical curvature group and abnormal cervical curvature group by JOA classification.Several spinal-pelvic parameters were measured on preoperative X-ray,including coronal parameters like main structural curve Cobb angle(MSA),proximal thoracic curve Cobb angle(PTA),T1 tilt angle(T1T),distance between C7 plumb line and center sacral vertical line(C7PL-CSVL),cervical sagittal parameters involving lordosis angle(CLA),C2-7 sagittal vertical axis(c SVA),C2 Slope(C2S)and T1 Slope(T1S),and other spinal-pelvic parameters containing upper thoracic kyphosis angle(UTKA),main thoracic kyphosis angle(MTKA),global thoracic kyphosis angle(GTKA),lumbar lordosis angle(LLA),pelvic tilt(PT),pelvic incidence(PI),sacral slope(SS),sagittal vertical axis(SVA),cervical thoracic pelvic angle(CTPA),T1 spino-pelvic inclination(T1 SPi)and T1 pelvic angle(TPA).The spinal-pelvic parameters were compared between two groups.Pearson correlation analysis and stepwise multilinear regression analysis were performed to analyze the relevance between the cervical curvature with other parameters.Results.The preoperative CLA of AIS patients in our study was-4.8 ± 15.4 degree,65.2% of AIS patients had abnormal cervical curvature.CLA(P<0.05),C2 Slope(P<0.05),T1 Slope(P<0.05),UTKA(P<0.05),MTKA(P<0.05)and GTKA(P<0.05)in abnormal CLA group were significantly different from that in normal CLA group.Pearson correlation coefficient showed that preoperative CLA had a strong correlation with C2 S,T1S and GTKA,had a moderate correlation with UTKA and had a weak correlation with MTKA and SVA.Neither statistical difference of coronal curvature and parameters in two groups nor correlation between coronal parameters and CLA had been found in our study.Stepwise multilinear regression analysis showed that preop CLA= 2.060-0.884 × preop T1 S + 0.860 × preop C2 S.Conclusion.Compared with asymptomatic peer,the proportion of abnormal cervical curvature was higher in AIS patients.The cervical curvature was related to some local sagittal parameters including C2 S,T1S,UTKA,MTKA and GTKA,and global sagittal parameter,namely SVA.While the coronal curvature and parameters were irrelevant with cervical curvature statistically.Part Ⅱ: Assessment of cervical disc degeneration and its relevance with cervical sagittal alignment in adolescent idiopathic scoliosisObjective.The aim of this study was to assess the cervical disc degeneration in adolescent idiopathic scoliosis(AIS)and to analyze its relevance with cervical curvature and other sagittal parameters.Method.A retrospective study was performed on 92 AIS patients treated by posterior spinal fusion in Xijing Hospital of the Air Force Medical University between July 2012 and November 2016.The patients were divided into normal cervical curvature group and abnormal cervical curvature group by JOA classification.The degree of cervical disc degeneration was accessed on preoperative cervical MRI by Pfirrmann grade.A novel scoring was calculated to quantify the degree of cervical disc degeneration.The cervical disc degeneration was compared between two groups.Spearman correlation analysis was performed to analyze the relevance between the cervical disc degeneration and sagittal parameters including CLA,c SVA,C2 S,T1S,UTKA,MTKA,GTKA,LLA,PT,PI,SS,SVA,CTPA,T1 SPi and TPA.Logistic regression analysis and receive operator characteristic(ROC)curve were performed to define the predictors of cervical disc degeneration.Results.42 patients(45.7%)in our study had cervical disc degeneration,with the highest proportion at C5/6 and lowest proportion at C2/3.The rate of cervical disc degeneration in abnormal curvature was 55.0%,which was higher than that in normal cervical curvature group(28.1%,p=0.016).Spearman correlation coefficient showed that the degree of cervical disc degeneration had a correlation CLA,C2 S,T1S,UTKA and GTKA.Logistic regression analysis showed that CLA was a risk parameter for cervical disc degeneration.ROC curves showed that patients with CLA≥-3.6° were more likely to have cervical disc degeneration.Conclusion.Compared with asymptomatic peer,the proportion of cervical disc degeneration was higher in AIS patients.The results showed a close relationship,an interaction and mutual influence between the cervical disc degeneration and cervical sagittal alignment.Abnormal cervical curvature was a risk factor for cervical disc degeneration.Part Ⅲ: The change of cervical curvature during postoperative follow-up and its related factors in adolescent idiopathic scoliosisObjective.The aim of this study was to analyze the sagittal compensatory mechanism of the cervical spine by the change of radiographic sagittal parameters before and after posterior spinal fusion and to define radiographic alignment parameters that can forecast the cervical sagittal alignment after long-term follow-up.Methods.A retrospective study was performed on 92 AIS patients treated by posterior spinal fusion in Xijing Hospital of the Air Force Medical University between July 2012 and November 2016.According to the change of CLA at 2-year follow-up vs preoperative,patients were divided into 4 groups,including normal Preop CLA-normal follow-up CLA group,normal Preop CLA-abnormal follow-up CLA group,abnormal Preop CLA-normal follow-up CLA group and abnormal Preop CLA-abnormal follow-up CLA group.Sagittal alignment parameters of spinal-pelvic were measured on immediate postoperative and 2-year follow-up X-ray,including cervical sagittal parameters involving CLA,c SVA,C2 S and T1 S,and other spinal-pelvic parameters containing UTKA,MTKA,GTKA,LLA,PT,PI,SS,SVA,CTPA,T1 SPi and TPA.Preoperative and follow-up sagittal parameters were compared among each group.Pearson correlation analysis,stepwise multilinear regression analysis,ROC curve and odds ratio were performed to define the predictors of cervical sagittal alignment and evaluate its power of predict.Results.The 2-year follow-up CLA of AIS patients in our study was-6.8 ± 14.8 degree,59.8% of patients had abnormal cervical sagittal alignment.The patients were divided into 4 groups including normal Preop CLA-normal follow-up CLA group(18 cases),normal Preop CLA-abnormal follow-up CLA group(14 cases),abnormal Preop CLA-normal follow-up CLA group(19 cases)and abnormal Preop CLA-abnormal follow-up CLA group(41 cases).Pearson correlation coefficient test showed that preoperative,postoperative and 2y follow-up CLA was correlated to corresponding C2 S,SVA,T1 S,UTKA,MTKA and GTKA.Stepwise multilinear regression analysis showed that follow-up CLA= 26.406 – 1.021 × postop GTKA + 0.124 × preop CLA.Furthermore,ROC curves showed that postoperative GTKA ≤ 34.3 degree was predictive of abnormal cervical curvature after longterm follow-up(OR=16.1).Conclusion.Thoracic curvature was closely correlated with cervical curvature in long-term follow-up.And its correction by surgery helped the improvement of postoperative cervical kyphosis.