The reliability of preoperative supine radiographs to predict the amount of curve flexibility in adolescent idiopathic scoliosis

STUDY DESIGN. Retrospective review. OBJECTIVE. To determine the reliability of supine long-cassette radiographs as compared with side-bending films in predicting curve flexibility in operative cases of adolescent idiopathic scoliosis (AIS). SUMMARY OF BACKGROUND DATA. The value of side-bending films is important in the classification of AIS, as well as predicting curve flexibility. METHODS. A total of 675 patients with a diagnosis of operative AIS were evaluated. All curves were classified by the Lenke classification. Coronal parameters included: proximal thoracic (PT), main thoracic (MT), and thoracolumbar/lumbar (TL/L) Cobb measurements; sagittal data including: T2-T5, T5-T12, and TL/L measurements. Curves were divided into Lenke Types 1 (N = 263), 2 (N = 118), 3 (N = 52), 4 (N = 31), 5 (N = 57), and 6 (N = 54). Lenke Types 1 to 4 (Group I-MT Major) were compared with Types 5 and 6 (Group II-TL/L Major). RESULTS. For Group I, MT supine films were highly predictive of MT side-bending while TL/L supine films were highly predictive of TL/L side-bending and standing films. An equation was derived to predict the value of the side-bending radiographs for each part of the curve. For Group II, MT supine films were highly predictive of MT side-bending and standing films. TL/L supine films were highly predictive of TL/L side-bending and standing films. Contingency table analysis for Group I resulted in the supine film providing a strong statistical ability to predict a nonstructural PT curve (sensitivity = 0.952, PPV = 0.864, NPV = 0.865) and also a nonstructural TL/L curve (sensitivity = 0.958, PPV = 0.916). Similarly, in Group II, we found a strong statistical ability to predict a nonstructural PT (sensitivity1.00, PPV = 0.982, NPV = 1.00) and a nonstructural MT curve (sensitivity 0.789, specificity = 0.842, PPV = 0.833, NPV = 0.80). CONCLUSION. A single preoperative supine radiograph is highly predictive of side-bending radiographs and can be used as an adjunct to predicting curve type, flexibility, and structurality. Thus, this singular, reproducible, and non-effort-related radiograph can potentially replace the need for dual side-bending films.