Prediction of Postoperative Curve Correction based on the Supine Radiographs for Adult Idiopathic Scoliosis (AdIS) patients

Background Context Preoperative supine radiographs are mandatory in the new AdIS classification. Supine radiographs are easily reproducible and highly predictive of side bending radiographs. However, few studies evaluated the use of supine radiographs in predicting postoperative curve correction after PSF in AdIS. Purpose To investigate the use of supine and side bending (SB) radiographs in predicting postoperative curve correction in Adult Idiopathic Scoliosis (AdIS) patients who underwent Posterior Spinal Fusion (PSF). Study Design Retrospective study Patient sample 93 AdIS patients who underwent PSF between 2022 and 2023 were included. Outcome Measures Demographic data were age, gender, height, weight, BMI, Risser grade, Lenke curve types and Cobb angles. Main outcome measures are pre-operative and immediate post-operative Cobb angle (proximal thoracic (PT), main thoracic (MT) and thoracolumbar/lumbar (TL/L) curves), Supine Cobb angle and Flexibility rate (PT, MT and TL/L), and Correction Rate (PT, MT and TL/L) Methods Correlation study was performed between supine Cobb angle vs. post-operative Cobb angle for PT, MT and TL/L curves. A predictive formula was derived from the correlation plots. Results A total of 93 subjects were included in our study with a median age of 24.7 years and comprised of 80 females (86.0%). Preoperative Supine Cobb angle (r=0.835, r=0.881, r=0.767, p<0.001) and preoperative SB Cobb angle (r=0.815, r=0.872, r=0.801, p<0.001) showed similar strong positive correlation with postoperative PT, MT and TL/L Cobb angle, but preoperative Supine Cobb angle had slightly stronger correlation in PT and MT, whereas preoperative SB Cobb angle had stronger correlation in TL/L curve. Using the derived predictive formulae, there was a significant, strong, positive correlation between the predicted value and actual value of postoperative standing Cobb angle, (r=0.852, P<0.001), with 71.0% of the patients had predicted postoperative Cobb angle from the supine radiographs within 5 degrees of the actual value. Conclusion Both supine radiographs and side bending radiographs had strong predictability of the postoperative Cobb angle for PT, MT and TL/L curves. In 71.0% of patients, the actual postoperative Cobb angle was within 5 degrees of the predicted postoperative Cobb angle using the predictive formulae.