Three-dimensional analysis of thoracic apical sagittal alignment in adolescent idiopathic scoliosis.

Methods: 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.

Background: 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.

Conclusions: 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.