Evaluating flexibility and predicting curve correction using fulcrum- bending radiographs in Lenke type 2 adolescent idiopathic scoliosis

Background: Fulcrum-bending (FB) correction is considered to provide the best estimation of main thoracic (MT) curve flexibility and postoperative correction in surgical treatment for adolescent idio-pathic scoliosis (AIS). However, few studies evaluated the usefulness of FB radiographs for proximal thoracic (PT) curve. We aimed to perform flexibility assessments using both active side-bending (SB) and FB radiographs and evaluate surgical outcomes after posterior spinal fusion (PSF) for Lenke type 2 AIS.Methods: This study included 38 consecutive patients with Lenke type 2 AIS who underwent PSF using a pedicle screw construct with a minimum 2-year follow-up. Radiographic parameters, including correction rate, SB and FB flexibility, and FB correction index (FBCI: [correction rate/FB flexibility] x 100), were evaluated preoperatively, immediately after surgery, and at the 2-year follow-up. The clinical outcomes were preoperatively evaluated using the Scoliosis Research Outcomes Instrument-22 and at the follow-up.Results: All scoliosis curves significantly improved and shoulder balance shifted toward left shoulder elevation (all comparisons, p < 0.0001). There were significant differences between the SB and FB cor-rections in the PT and MT curves (p < 0.0001). The magnitudes of the discrepancies between the SB and FB corrections in the PT and MT curves were 11.2 degrees +/- 5.2 degrees and 11.6 degrees +/- 7.2 degrees, respectively. FB correction did not differ from postoperative Cobb angles correction immediately after surgery or at the 2-year follow-up; the mean FBCIs in the PT and MT curves were 98.8% and 105.5%, respectively. The self-image domain SRS-22 scores had significantly increased at the 2-year follow-up (p < 0.0001).Conclusions: There were significant differences between the SB and FB corrections, and FB correction tended to approximate the postoperative curve correction (FBCI = 100%) for PT and MT curves in patients with Lenke type 2 AIS. FB flexibility is more reliable than SB flexibility in evaluating actual curve flexi-bility even for the PT curve.(c) 2022 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.