Influence Of The Location Of Kyphotic Apical Vertebra On Spino-pelvic Sagittal Plane With Adult Spinal Deformity

Background.The incidence rate of adult spinal deformity(ASD)is becoming increasingly high due to the aging of society.Spinal sagittal alignment has been demonstrated to play a more important role in pain and functional disability than coronal alignment.Therefore,it is essential to identify a feasible assessment method to evaluate the spinal sagittal shape for ASD patients.The kyphotic apical vertebra(KAV)can reflect the location of deformity;meanwhile,different locations of KAV could affect regional spinal alignment and cause according compensatory mechanisms,leading to a specific global spinal shape eventually.Therefore,KAV can assess the spino-pelvic sagittal plane as a new parameter.However,the research about KAV is little at home and abroad.This study would research the influence of KAV on spino-pelvic sagittal plane.Objective.The aim of this study was to explore the influence of KAV on the local and global spino-pelvic sagittal alignment,to research the corresponding compensatory mechanisms based on different locations of spinal deformity,and to investigate its reliability as a spino-pelvic sagittal parameter.Methods.Patients with spinal diseases were enrolled in this retrospective study from Shandong Provincial Hospital between January 2017 and August 2018.The radiographic diagnosis of ASD was defined by the presence of at least one of the following conditions:coronal Cobb angle more than 20°,sagittal vertical axis(SVA)more than 50 mm,pelvic tilt(PT)more than 25°,or thoracic kyphosis(TK)more than 60°.The exclusion criteria were(1)fresh vertebral fractures,(2)spinal tumors or infection,(3)ankylosing spondylitis,or(4)neurological and neuromuscular diseases.Full-spine lateral standing radiographs were obtained from all ASD patients.The following parameters were also measured:thoracic kyphosis(TK),thoracolumbar kyphosis(TLK),lumbar lordosis(LL),lower lumbar lordosis(LLL),sacral slope(SS),pelvic tilt(PT),pelvic incidence(PI),pelvic compensatory rate(PT/P1),pelvic incidence minus lumbar lordosis(PI-LL),sagittal vertical axis(SVA),and T1 pelvic angle(TPA).The location of the KAV of each subject was recorded by two spinal surgeons to assess the reliability of the method.Intraclass correlation coefficient(ICC)analysis was performed to assess the imterobserver and intraobserver reliability of KAV assessment.According to the different location of KAV and diverse spinal shapes,all subjects were divided into 2 types:I type(no KAV)and II type(KAV exists).I type was divided into 2 groups based on spinal shape:A group(SVA 50mm)and B group(SVA>50mm).Ⅱ type was divided into 4 groups based on the location of KAV:upper thoracic group(T1≤KAV<T5),thoracic group(T5 KAV<T10),thoracolumbar group(T10≤KAV<L2),lumbar type(L2≤KAV≤L5).A two-sample t test or one-way analysis of variance(ANOVA)was used for comparisons of radiographic parameters among the different groups.The statistical significance threshold was set at P<0.05.Results.165 patients(age range:19-74 years old)with ASD were enrolled in this retrospective study.Among the patients,there were 75 males and 90 females,and the mean age was 50.5 ± 14.6 years old.The interobserver and intraobserver reliability of the KAV measure revealed excellent agreement(ICC=0.990 and 0.984,respectively).Significant differences in major radiographical parameters were observed among different types of deformities,which allowed distinct types of spinal deformities to be distinguished.Conclusion.For ASD patients,there exist respective characters in the spino-pelvic plane of different KAV location.The KAV can reflect the location of deformity;meanwhile,different locations of KAV could affect regional spinal alignment and cause according compensatory mechanisms,leading to a specific global spinal shape eventually.A new assessment method based on the KAV location provides greater feasibility and reliability in evaluating spinal sagittal shape for ASD.