| BackgroundIdiopathic scoliosis(IS)is a three-dimensional deformity that usually affects the coronal and sagittal planes of patients.For a long time,the main goal of the treatment and surgical strategy of spinal deformity correction is to correct the scoliosis deformity on the coronal plane and prevent the further development of the disease.However,with the continuous progress of spinal deformity research,a large number of studies have shown that there is a significant correlation between the pain and activity limitation of IS patients and their spinal sagittal deformity.Therefore,more and more attention has been paid to the correction of sagittal deformity in recent years,and it has been confirmed that it is very important to improve the long-term quality of life and treatment satisfaction of patients.Among them,the change of cervical sagittal curvature plays a key role in affecting the arrangement of thoracolumbar spine and pelvic tilt.At the same time,the deterioration of cervical sagittal curvature will also cause pain.Therefore,correctly evaluating the influencing factors of cervical curvature is one of the key measures to improve the prognosis of patients.T1 slope,as one of the key radiological parameters,has become an important parameter to evaluate cervical balance in many studies.It is helpful to understand the cause and origin of cervical deformity in patients with IS.However,on the X-ray lateral film,T1 vertebral endplate is often blocked due to the influence of anatomical position and obesity.On the X-ray film of IS patients,in addition to the above factors,due to the imbalance of sagittal plane of spine and the existence of spinal deformity,T1 slope is more difficult to be clearly displayed than ordinary people.At the same time,in the postoperative imaging evaluation,the visibility of T1 slope will be more disturbed due to the existence of upper thoracic implants.Therefore,it is worth studying to find new sagittal parameters that can replace T1 slope in patients with IS and verify the feasibility of evaluating cervical sagittal balance instead of T1 slope.This study intends to use C7 slope instead of T1 slope to evaluate the sagittal balance of cervical spine in patients with IS during long-term follow-up.ObjectiveThe purpose of this study was to explore whether C7 slope can be used instead of T1 slope in patients with IS when T1 vertebral endplate is not visible on cervical X-ray lateral film.In addition,further analyze the risk factors of cervical kyphosis during the follow-up,and verify whether C7 slope can replace T1 slope to evaluate the sagittal balance of cervical spine in patients with IS.MethodsFrom January 2009 to December 2020,we retrospectively analyzed 132 IS patients with is who underwent posterior spinal fusion in our hospital After excluding patients with invisible vertebral endplates,the upper C7/lower C7/upper T1 vertebral endplates of 71 patients were all visualized on lateral cervical spine radiographs preoperatively,postoperatively,and at last follow-up.The main curve angle(MA),cervical lordosis(CL),upper C7 slope,lower C7 slope,T1 slope,upper thoracic kyphosis(UTK),main thoracic kyphosis(MTK),lumbar lordosis(LL),sagittal vertical distance of the spine(SVA),cervical spine(CSVA),pelvic tilt(PT),pelvic incidence(PI),and sacral slope(SS)were measured on the full-length positive and lateral X-ray film of the spine.At the same time,the basic baseline data of the patients were collected.Pearson correlation coefficient was used to evaluate the correlation strength between upper C7 slope and T1 slope,and lower C7 slope and T1 slope.Through the upper and lower slopes of C7,simple linear regression analysis is used to generate linear regression equation to predict T1 slope.The patients were subsequently divided into cervical kyphosis group and cervical lordosis group according to their cervical curvature status at the last follow-up,and the differences in the parameters between the two groups were compared by the independent samples t-test.The preoperative and postoperative variables with statistically significant differences were included in the binary logistic regression analysis(forward method)to identify the independent risk factors associated with cervical kyphosis at the postoperative follow-up for IS patients.Using R to construct nomogram for visual analysis and the receiver operating characteristic curve(ROC)was used to analyze and compare the prediction models to explore whether C7 slope can replace T1 slope to predict the sagittal balance of cervical spine at the last follow-up.ResultsAccording to our statistics,the visibility rate of the C7 upper endplate was 93.9%before operation,94.7%after operation,and 92.4%at the last follow-up.The lower C7 endplate’s visible rate was 77.3%before operation,75.0%after operation,and 73.5%at the last follow-up.The visible rate of T1 upper endplate were 60.6%,56.8%and 59.1%before operation,after operation and at the last follow-up,respectively.Linear regression analysis showed that the upper C7 slope and T1 slope in IS patients,regardless of preoperative(r=0.876,P<0.01),postoperative(r=0.858,P<0.01),last follow-up(r=0.895,P<0.01)and overall(r=875,P<0.01);There was also a significant strong correlation between lower C7 slope and T1 slope before operation(r=0.881,P<0.01),after operation(r=0.887,P<0.01),follow-up(r=0.935,P<0.01)or overall(r=0.903,P<0.01).Among the included patients,37 patients with CL less than 0° at the last follow-up were included in the cervical kyphosis group,and 34 patients with CL greater than 0° at the last follow-up were included in the cervical lordosis group.Bringing the indicators of significant differences between the two groups(P<0.01)into the binary logistic regression analysis revealed that the preoperative CL and the postoperative T1 slope/upper C 7 slope/lower C7 slope were independent risk factors for the cervical kyphosis at the last follow-up after surgery in IS patients.ROC analysis showed that the three prediction models and nomograms constructed by postoperative T1 slope,C7 upper slope,C7 lower slope and preoperative CL had a strong predictive effect on the occurrence of cervical kyphosis during follow-up(AUC=0.87,0.87 and 0.85),and there was no significant difference between the models(P>0.05).ConclusionThere was a significant strong correlation between upper or lower C7 slope and T1 slope in patients with IS.In the prediction of cervical kyphosis in the last follow-up of IS patients,preoperative CL and postoperative T1 slope,upper and lower C7 slope are independent risk factors.The three models and nomograms constructed by postoperative T1 slope,C7 upper and lower slope and preoperative CL have strong predictive effect.Among them,because of the higher visibility rates on upper C7 slope,we prefer to use the upper C7 slope to replace T1 slope.In conclusion,when the T1 vertebral endplate is not visible on the lateral X-ray film of the cervical spine in patients with IS,the C7 slope can replace the T1 slope and achieve the predictive effect of evaluating the sagittal balance of the cervical spine. |
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