Factors of thoracic cage deformity that affect pulmonary function in adolescent idiopathic thoracic scoliosis

STUDY DESIGN. This clinical study examined the association between pulmonary function and thoracic cage deformities in scoliosis. OBJECTIVE. To determine the factors in spinal and thoracic cage deformities that affect pulmonary function in scoliosis. SUMMARY OF BACKGROUND DATA. Pulmonary function in scoliosis has generally been evaluated in terms of lateral spinal curvature. No previous report has evaluated changes in pulmonary function taking into consideration measurements reflecting not only spinal curvature but also thoracic cage deformities, although scoliosis is a three-dimensional deformity. METHODS. A total of 109 patients (mean age, 14.2 years) with adolescent idiopathic right thoracic scoliosis (mean lateral spinal curvature, 37.7°) had full assessment of pulmonary function and a radiographic evaluation from radiographs of the whole spine, Moiré topography, and thoracic computed tomography. RESULTS. Multiple regression analysis (stepwise method) was performed at each vertebral level from T3-T12 to identify the factor that most strongly affects %VC. The correlation coefficient was highest at T9 and next highest at T8, with values of 0.641 (r = 0.411, P < 0.0001) and 0.625 (r = 0.390, P < 0.0001), respectively. At T9, multiple regression analysis showed that the sagittal diameter of the thoracic cage and the total lung area were identified as factors that most strongly affect %VC. Similarly, the sagittal diameter of the thoracic cage and the rotation angle to the sagittal plane were identified at T8. CONCLUSIONS. The factors that reduced %VC were the sagittal diameter of the thoracic cage, total lung area and vertebral rotation at the T8 and T9 levels.