Assessment of Curve Flexibility in Idiopathic Scoliosis Patients With Severe Scoliosis (Cobb Angle ≥ 90 o ): Comparison Between the Supine Traction Radiograph Versus the Physician Supervised Supine Side Bending Radiographs

Study design Retrospective study. Objective To analyze the flexibility of severe scoliosis with cobb angle ≥90 o , comparing between the supine traction radiograph versus the physician supervised supine side bending film. Methods 72 severe idiopathic scoliosis patients between 2015 to 2023 in a single academic institution who underwent single-staged posterior spinal fusion with curves more than ≥90 o with available anteroposterior, traction and side bending radiographs were recruited. Results 58 patients had severe curves in the main thoracic (MT) region, with mean preoperative Cobb angle of 107.3±16.6° and postoperative Cobb angle of 51.2±15.5°. 18 patients had severe curves at thoracolumbar/lumbar (TL/L) region, with mean preoperative Cobb angle of 99.8±8.2° and postoperative Cobb angle of 45.2±12.8°. The correction rates for MT and TL/L curve is 52.7±11.1° and 55.0±11.1° respectively. No significant differences were observed between sidebending (SB) and traction radiographs in assessing MT curve flexibility (34.7±12.4% vs. 34.5±11.8%, respectively; p=0.907) or in the corresponding correction indices (1.7±0.5 vs. 1.7±0.9, respectively; p=0.461). However, TL/L curves had a significant difference in flexibility comparing SB (46.0±12.6%) and traction radiographs (42.0±11.5%) (p=0.008) and comparing the side bending correction index (SBCI) (1.2±0.2) and traction correction index (TCI) (1.4±0.3) (p=0.010). The SBCI for TL/L curve was closer to 1, indicating that the Cobb angle on SB radiographs for TL/L curves could more accurately predict the postoperative Cobb angle. Conclusion In severe TL/L curves, physician-supervised supine side bending (PSSB) radiographs may provide a more accurate assessment of curve flexibility, as reflected by a correction index closer to 1. These findings suggest that PSSB radiographs may be a useful radiographic assessment for evaluating TL/L curve flexibility and guide preoperative planning in patients with severe idiopathic scoliosis.