The effects of the three-dimensional deformity of adolescent idiopathic scoliosis on pulmonary function

Utilizing 2D measurements, previous studies have found that in AIS, increased thoracic Cobb and decreased thoracic kyphosis contribute to pulmonary dysfunction. Recent technology has improved our ability to measure and understand the true 3D deformity in AIS. The purpose of this study was to evaluate which 3D radiographic measures predict pulmonary dysfunction.

One hundred and sixty-three surgically treated AIS patients with preoperative PFTs (FEV, FVC, TLC) and EOS^® imaging were identified at a single center. Each spine was reconstructed in 3D to obtain the true coronal, sagittal, and apical rotational deformities. These were then correlated with the patient's preoperative PFT measurements. Regression analysis was performed to determine the relative effect of each radiographic measure.

There were 124 thoracic and 39 lumbar major curves. The range of preoperative thoracic and lumbar 3D coronal angle was 11-115° and 11-98°, respectively. The range of preoperative thoracic 3D kyphosis (T5-T12) and thoracic apical vertebral rotation was -56 to 44° and 0-29°, respectively. Increasing thoracic 3D Cobb and thoracic vertebral rotation and decreasing thoracic 3D kyphosis most significantly correlated with decreasing pulmonary function, especially FEV. In patients with the largest degree of thoracic deformity (3D Coronal Cobb > 80°, 3D thoracic lordosis >20°, and absolute apical rotation >25°), the majority of patients had moderate to severe pulmonary impairment (≤65 % predicted). 3D thoracic kyphosis was the most consistent predictor of FEV (r ² = 0.087), FVC (r ² = 0.069), and TLC (r ² = 0.098) impairment.

Larger thoracic coronal, sagittal, and axial deformities increase the risk of pulmonary impairment in patients with AIS. Of these, decreasing 3D thoracic kyphosis is the most consistent predictor. This information can guide surgeons in the decision making process for determining which surgical techniques to utilize and which component of the deformity to focus on.