Purpose: The objective was to analyse the effect of thoracic morphology on pulmonary function in adolescent idiopathic scoliosis (AIS) to predict preoperative lung function.
Methods: A total of 170 consecutive preoperative patients (average age 15.1 years) with Lenke 1 and 2 AIS underwent pulmonary function testing. Thirteen deformity parameters, including rib hump size, rib asymmetry, spinal intrusion and thoracic/lung dimensions in the sagittal and coronal plane, were measured on whole-spine radiographs. Lung function parameters were expressed as z-scores. Correlation and regression analysis of these parameters with lung function were performed.
Results: Mean thoracic Cobb (MT) was 69.1°, and mean T5-T12 thoracic kyphosis (TK) was 21.8°. MT correlated significantly with FEV1 and FVC (rs = - 0.40 and - 0.38). TK correlated weakly with FEV1 and FEV1/FVC (rs = 0.23 and 0.25). FEV1 and FVC were best predicted by the inverse apical vertebra body-rib ratio (AVBRr-1, rs = 0.46 and 0.42), rib hump depth index (RHDi, rs = - 0.52 and - 0.50) and spinal intrusion ratio (SIr, rs = - 0.50 and - 0.45). The kyphosis-lordosis index (KLi) correlated with FEV1/FVC (rs = 0.29). Multivariate regression analysis of coronal and sagittal Cobb angles produced a model which explained 35% and 30% of the variance in FEV1 and FVC, whilst a regression model consisting of AVBRr-1 and SIr was able to predict 54% and 48%.
Conclusion: AVBRr-1, RHDi and SIr measured on posterior-anterior and lateral radiographs provide better estimations of lung function in preoperative AIS patients than Cobb measurements. KLi was an indicator of airway obstruction as measured by FEV1/FVC.
Keywords: Pulmonary function tests; Rib hump; Scoliosis; Spinal intrusion; Thoracic deformity.