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

Abstract

BackgroundFulcrum-bending (FB) correction is considered to provide the best estimation of main thoracic (MT) curve flexibility and postoperative correction in surgical treatment for adolescent idiopathic 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. MethodsThis 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] × 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. ResultsAll 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 corrections 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° ± 5.2° and 11.6° ± 7.2°, 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). ConclusionsThere 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 flexibility even for the PT curve.