Prediction of long-term postoperative results of disc wedge and vertebral tilt with intraoperative prone radiograph in posterior correction of thoracolumbar/lumbar curve in adolescent idiopathic scoliosis: a minimum 5-year follow-up

BACKGROUND CONTEXT Preservation of the more mobile lumbar segments is important during thoracolumbar/lumbar scoliosis surgery; however, the remaining disc wedge angle (DWA) below lowermost instrumented vertebra (LIV) and vertebral body tilt below LIV (LIV+1 tilt) can cause curve progression. PURPOSE This study aimed to evaluate the efficacy of intraoperative radiograph to predict the postoperative DWA below LIV and LIV+1 tilt on standing radiographs in patients with LIV of L3 or L4. STUDY DESIGN/SETTING Retrospective cohort study PATIENT SAMPLE A total of 235 patients with idiopathic scoliosis who underwent posterior correction and fusion for the structural thoracolumbar curve and were followed up for >5 years were reviewed. OUTCOME MEASURES DWA below LIV, LIV+1 tilt, Cobb angle, trunk shift, apical vertebra translation, and pelvic parameters were measured. METHODS Correlation between intraoperative and postoperative measurements of DWA below LIV and LIV+1 tilt were assessed. Additional analysis was performed to identify risk factors and prognosis of LIV+1 tilt ≥10° and DWA below LIV of ≥4° RESULTS LIV+1 tilt measured on intraoperative radiograph was significantly correlated with the postoperative 5-day and postoperative 5-year evaluation in both groups. However, the intraoperative DWA below LIV was only correlated with the postoperative 5-year value in the L3 group (p=.018). At the 5-year follow-up, patients with LIV+1 tilt ≥10° on intraoperative radiography showed significantly greater LIV+1 tilt (p<.001), apical vertebral translation (p<.001), thoracic curve (p=.008), and thoracolumbar curve (p<.001) than patients with LIV+1 tilt <10°. Intraoperative DWA below LIV of ≥4° was only associated with higher DWA below LIV at the 5-year follow-up. CONCLUSIONS Intraoperative measurement of LIV+1 tilt was correlated with long-term postoperative outcomes, and intraoperative LIV+1 tilt ≥10° was associated with a less favorable radiographic outcome. Intraoperative DWA below LIV demonstrated less correlation with postoperative values and was not a prognostic factor for other radiographic parameters.