A reliability and validity study for different coronal angles using ultrasound imaging in adolescent idiopathic scoliosis

Background Context Radiation exposure remains a big concern in adolescent idiopathic scoliosis (AIS). Ultrasound imaging of the spine could significantly reduce or possibly even eliminate this radiation hazard. The spinous processes (SPs) and transverse processes (TPs) were used to measure the coronal deformity. Both landmarks provided reliable information on the severity of the curve as related to the traditional Cobb angle. However, it remained unclear which coronal ultrasound angle is the most appropriate method to measure the curve severity. Purpose The objective of this study was to test the reliability and the validity of several ultrasound angle measurements in the coronal plane as compared with the radiographic coronal Cobb angle in patients with AIS. Study Design/Setting This is a cross-sectional study. Patient Sample The study included 33 patients with AIS, both male and female (Cobb angle range: 3°–90°, primary and secondary curves), who underwent posterior-anterior radiography of the spine. Outcome Measures The outcome measures were the reliability (intraclass correlation coefficients [ICCs] for the intra- and interobserver variabilities) and the validity (linear regression analysis and Bland-Altman method, including the mean absolute difference [MAD]) of different ultrasound measurements. Materials and Methods The patients were scanned using a dedicated ultrasound machine (Scolioscan, Telefield Medical Imaging Ltd, Hong Kong). The reliability and the validity were tested for three coronal ultrasound angles: an automatic and manual SP angle and a manual TP angle as compared with the radiographic coronal main thoracic or (thoraco)lumbar Cobb angles. Results The ICC showed very reliable measurements of all ultrasound methods (ICC ≥0.84). The ultrasound angles were 15%–37% smaller as compared with the Cobb angles; however, excellent linear correlations were seen between all ultrasound angles and the Cobb angle (thoracic: R2≥0.987 and (thoraco)lumbar R2≥0.970), and the Bland-Altman plot showed a good agreement between all ultrasound angles and the Cobb angle. The MADs of the ultrasound angles, corrected using the linear regression equation, and the Cobb angles showed no significant difference between the different ultrasound angles (MAD: automatic SP angle 4.9°±3.2°, manual SP angle 4.5°±3.1°, and manual TP angle 4.7°±3.6°; p≥.388). Conclusions Coronal ultrasound angles are based on different landmarks than the traditional Cobb angle measurement and cannot represent the same angle values. In this study, we found excellent correlations between the ultrasound and Cobb measurements, without differences in the reliability and validity between the ultrasound angles based on the SPs and TPs. Therefore, the severity of the deformity in patients with AIS can be assessed by ultrasound imaging, avoiding hazardous ionizing radiation and enabling more individualized patient care. It also opens possibilities for screening.