Correlation Between Three-Dimensional Radiographic Spinal Parameters and Pulmonary Function Tests in Patients With Adolescent Idiopathic Scoliosis

Study Design: Cross-sectional study. Objective: To evaluate the relationship between pulmonary function tests (PFTs) and spinal deformity. Summary of Background Data: The relationship between three-dimensional (3D) spinal deformity and pulmonary status in adolescent idiopathic scoliosis (AIS) is not fully understood. Materials and Methods: Prospectively collected data from consecutive AIS patients from October 2020 to December 2023 were retrospectively reviewed. Preoperative PFTs measured forced expiratory volume (FEV), forced vital capacity (FVC), and total lung capacity (TLC). The percent of predicted values was classified using American Thoracic Society guidelines. 3D reconstructions were created from biplanar radiographs. Correlations were performed between PFTs and radiographic deformities, clinical variables, and patient-reported outcome measures (PROMs). Results: A total of 101 AIS patients with a mean 88% FEV, 91% FVC, and 88% TLC were included. Over 40% had pulmonary impairment, including 13.3% with moderate-to-severe impairment in at least one PFT. These patients had larger upper thoracic curves (UTC) (32 vs. 25°, P =0.007), less 3D thoracic kyphosis (0.6 vs . 8.6°, P =0.021), smaller lumbar curves (30 vs . 44°, P =0.038), and less lumbar rotation (11 vs . 18°, P =0.008). Main thoracic curve (MTC) moderately correlated with %FEV ( r =−0.38), %FVC ( r =−0.34), and %TLC ( r =−0.38) (all P <0.001). UTC moderately correlated with %FEV ( r =−0.35) and %TLC ( r =−0.34) (both P ≤0.001), with a trend toward a positive correlation between 3D kyphosis and FEV ( r =0.29, P =0.006). Thoracic scoliometer measurements moderately correlated with %FEV ( r =−0.40, P <0.001), but there were no significant correlations between axial rotation or PROMs and PFTs. On regression analysis, MTC accounted for 10.7% of the variation in %FVC. Conclusion: In patients with AIS, there was a moderate correlation between thoracic curve magnitude and reduced pulmonary function, a higher incidence of pulmonary impairment with 3D thoracic hypokyphosis, with no significant association between axial rotation or PROMs and PFTs. The MTC magnitude accounts for a small portion of the variation seen in PFTs.