Exploring the use of biphasic quantitative thoracic computed tomography to evaluate halo-pelvic traction in managing severe adolescent idiopathic scoliosis

Background: Patients diagnosed with severe adolescent idiopathic scoliosis (AIS) often experience reduced pulmonary function and lung volume due to deformities in the spine and ribcage. Presurgical halo-pelvic traction (HPT) has been used to treat severe scoliosis before second-stage surgery. Nevertheless, there is a scarcity of studies utilizing computed tomography (CT) scans to evaluate changes in lung volume post-HPT. Therefore, this study aimed to investigate changes in lung volumes and anatomical parameters using biphasic CT scans following HPT in AIS patients. The hypothesis was that the lung tidal volume, as determined by biphasic CT scans, would exhibit changes in conjunction with pulmonary function. Methods: The study comprised a cohort of 24 patients with AIS scheduled for presurgical HPT intervention. Pre- and post-traction radiographs, biphasic CT scans, and pulmonary function tests (PFTs) were obtained. Then, 3-dimensional (3D) reconstructions were generated from the CT scans obtained at both end inspiration and end expiration to calculate various measurements of lung volumes, particularly the lung tidal volume. Additionally, various thoracic anatomical parameters and clinical parameters, including PFTs, were assessed and compared. Results: Following an average of 91.7 days of HPT, a significant increase in CT total lung volume (TLV) was noted at both end inspiration (P<0.001) and expiration (P=0.020). Conversely, there was no significant change in lung tidal volume (P=0.115). The traction resulted in significant reductions in the thoracic Cobb angle, kyphosis, and hemithoracic symmetry ratio, with average decreases of 32.9%, 33.0%, and 18.8%, respectively, accompanied by notable enhancements in PFTs. Changes in radiographic and CT parameters, excluding TLV at end expiration and hemithoracic symmetry ratio, were not correlated with PFT changes. Significant correlations were found between HPT duration and changes in the Cobb angle (r=−0.688, P<0.001) and left lung volumes at end inspiration (r=0.518, P=0.010) and expiration (r=0.452, P=0.027). Despite the enhancement in pulmonary function after HPT, CT lung tidal volume remained unchanged. This discrepancy contradicts our initial hypothesis, suggesting that CT lung tidal volume is not a reliable indicator of pulmonary function. Conclusions: Preoperative HPT significantly improved spinal deformity, TLV, and pulmonary function. The alteration in CT lung tidal volume did not correlate with PFTs and was deemed an unreliable predictor of pulmonary function. The use of biphasic thoracic CT for calculating lung tidal volume did not demonstrate substantial benefits over monophasic CT and is not recommended for severe AIS.