Impact of Cobb angle severity on pulmonary function and functional capacity in idiopathic scoliosis: a cross-sectional study using respiratory oscillometry and six-minute walk test

Purpose Thoracic deformity in idiopathic scoliosis may impair respiratory mechanics and functional capacity, particularly in severe curves. This study investigated the impact of Cobb angle severity on pulmonary function, respiratory mechanics, and functional performance in individuals with idiopathic scoliosis. Methods Sixteen controls and 48 individuals with idiopathic scoliosis (Cobb angle > 10°) and no pulmonary or cardiac comorbidities were evaluated. Patients were stratified into three groups according to Cobb angle severity: 10°–45°, 46°–70°, and > 70°. Pulmonary function was assessed using spirometry and plethysmography, respiratory mechanics were analyzed using oscillometry, and functional capacity was evaluated with the six-minute walk test (6MWT). Results Increasing Cobb angle was associated with progressive reductions in spirometric parameters (FVC, FEV₁, and FEF₂₅–₇₅) and plethysmographic measures (VC and TLC), along with increases in residual volume and the RV/TLC ratio. Oscillometric analysis revealed increased airway resistance (R4, R12, and R20), higher resonance frequency (fr) and reactance area (Ax), and reductions in mean reactance (Xm) and dynamic compliance (Cdyn), particularly in curves exceeding 70°. Functional capacity assessed by the 6MWT also declined with increasing deformity severity. Significant correlations were observed between Cobb angle and spirometric (FEV₁, R = − 0.542), plethysmographic (VC, R = − 0.492), and oscillometric (Cdyn, R = − 0.475) parameters. Conclusions Greater Cobb angle severity is associated with progressive impairment of pulmonary function, respiratory mechanics, and functional capacity in idiopathic scoliosis. Oscillometry may offer valuable complementary information on respiratory mechanics and could enhance the clinical assessment of pulmonary impairment in patients with moderate to severe idiopathic scoliosis.