In healthy subjects, respiratory maximal volumes are highly dependent on the sagittal range of motion of the T7-T10 segment. In AIS, the abolition of T7-T10 dynamics related to the stiffness induced by the apex region in Lenke IA curves could harm ventilation during maximal breathing. The aim of this study was to analyze the dynamics of the thoracic spine during deep breathing in AIS patients and in healthy matched controls. This is a cross-sectional, case-control study. 20 AIS patients (18 girls, Cobb angle, 54.7 ± 7.9°; Risser 1.35 ± 1.2) and 15 healthy volunteers (11 girls) matched in age (12.5 versus 15.8 years mean age) were included. In AIS curves, the apex was located at T8 (14) and T9 (6). Conventional sagittal radiographs of the whole spine were performed at maximal inspiration and exhalation. The ROM of each spinal thoracic functional segment (T1-T7, T7-T10, T10-T12) and the global T1-T12 ROM were measured. In healthy subjects, the mean T1-T12 ROM during forced breathing was 16.7 ± 3.8. AIS patients showed a T1-T12 ROM of 1.1 ± 1.5 (p < 0.05), indicating a sagittal stiffness of the thoracic spine. A wide T7-T10 ROM (15.3 ± 3.0) was found in healthy controls (91.6% of the T1-T12 ROM). AIS patients showed only 0.4 ± 1.4 ROM at T7-T10 (36.4% of the T1-T12 ROM) (p < 0.001). There was a linear relationship between the magnitude of T7-T10 kyphosis in maximal exhalation and both FVC (% of predicted FVC) and FEV1. In conclusion, Lenke 1A AIS patients show a restriction of the thoracic spine motion with an almost complete abolition of T7-T10 ROM, a crucial segment for deep breathing. T7-T10 stiffness could explain the ventilatory limitations found in AIS patients.
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