Predicting preoperative pulmonary function in patients with thoracic adolescent idiopathic scoliosis from spinal and thoracic radiographic parameters

The objective was to analyse the effect of thoracic morphology on pulmonary function in adolescent idiopathic scoliosis (AIS) to predict preoperative lung function. 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. 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%. 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.