Three-Dimensional Analysis of Thoracic Apical Sagittal Alignment in Adolescent Idiopathic Scoliosis

Study Design. Retrospective review of a series of adolescent idiopathic scoliosis patients. Objective. To perform a 3-dimensional (3D) analysis of patients with thoracic scoliosis to identify differences in the thoracic sagittal alignment measured from the standard lateral projection as compared to the true lateral view. Summary of Background Data. It has been difficult to clinically obtain radiographs in the planes of maximum spinal deformity. Recently, 3D models of the spine have been developed using biplanar radiographic reconstructions that allow a more accurate assessment of spinal alignment. Methods. Three-dimensional spinal reconstructions using biplanar radiographs were used to evaluate the apical thoracic sagittal profile. A measurement of sagittal curvature from 2 vertebral levels above and below the thoracic apex (5 vertebrae) was recorded from the standard lateral view. The 3D reconstructions were then rotated to achieve a true lateral view of the apical thoracic vertebra and the sagittal apical curvature was remeasured. The difference in the 2 measures of sagittal thoracic apical alignment was compared using repeated measures ANOVA, and then correlated to the coronal thoracic Cobb magnitude using a Pearson correlation analysis (P < 0.05). Results. Sixty-six adolescent idiopathic scoliosis patients with right thoracic scoliosis (Cobb averaged 47 degrees +/- 10 degrees) were evaluated. The apical thoracic sagittal curvature in the standard lateral view averaged 11 degrees +/- 10 degrees of kyphosis (range: -8 degrees to 38 degrees). This was statistically greater (P < 0.001) than the apical sagittal curvature in the true lateral view that averaged 1 degrees +/- 9 degrees ( range: -23 degrees to 22 degrees). The standard lateral view was rotated an average of 13 degrees +/- 4 degrees to achieve the ideal lateral view of the thoracic apex. Conclusion. This 3D analysis of thoracic scoliosis demonstrated a consistent loss of kyphosis within the 5 thoracic apical vertebrae. The true apical sagittal profile was found to be overestimated by an average of 10 degrees as compared to the perceived alignment from standard lateral radiographs.