Downloaded from http://journals.lww.com/spinejournal by BhDMf5ePHKbH4TTImqenVJrtsMDDBIGOXtXkF6RFeC5P+6/jK8XJlWZKXBTLz5yx on 10/16/2020 Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved. Postoperative Distal Coronal Decompensation After Fusion to L3 for Adolescent Idiopathic Scoliosis Is Affected by Sagittal Pelvic Parameters So Kato, MD, PhD, a,b,c Reinhard D. Zeller, MD, ScD, FRCSC, a Sofia P. Magana, BSc, a,b Mario Ganau, MD, PhD, FEBNS, FACS, b Yasushi Oshima, MD, PhD, c Sakae Tanaka, MD, PhD, c and Stephen J. Lewis, MD, MSc, FRCSC a,b Study Design. Retrospective study. Objective. To identify on early postoperative radiographs the risk factors for late distal decompensation in adolescent idio- pathic scoliosis (AIS) patients undergoing posterior fusion surgery to L3. Summary of Background Data. Sparing distal fusion levels in AIS surgery is considered beneficial for postoperative mobility and outcomes; nonetheless, late distal decompensation is of concern. L3 is often advocated as lower instrumented vertebra in posterior fusion, but progressive angulation of the L3/4 disc is commonly observed. Methods. A retrospective analysis was conducted on 78 AIS patients who underwent posterior fusion to L3 from 2007 to 2014. Patients’ demographic data, early and 2-year postoperative standing radiographs by biplanar imaging system were investigated. Late decompensation was defined as progressive increase of L3–4 disc wedging angle at 2-year follow-up. Coronal, sagittal, and rotational radiographic parameters were compared between those with and without decompensation. SRS-30 scores were reviewed. Results. Mean age was 14.5-year, and fusion levels averaged 12.0 (range: 6–15); 43 out of 78 patients (55%) experienced progressive L3-4 disc wedging, with 6 showing wedging >58. L3 translation from the central sacral vertical line (13.9 vs. 11.1 mm, P ¼ 0.13) and increased pelvic tilt (13.38 vs. 8.68, P ¼ 0.06) on the early postoperative radiograph were associated with increased L3-4 disc wedging. Multivariate analysis revealed that larger pelvic tilt was a significant risk factor for decompen- sation (odds ratio ¼ 1.1 per 18, 95% confidence interval: 1.0– 1.1, P ¼ 0.04). SRS-30 scores did not differ significantly between the two groups (4.0 vs. 4.1, P ¼ 0.44). Conclusion. Pelvic retroversion and increased translation of L3 from the central sacral line on the early postoperative radiograph were associated with late L3-4 disc wedging in AIS fusions to L3. Careful surgical planning and correction of sagittal alignment are imperative to ensure the long-term outcomes. Key words: adolescent idiopathic scoliosis, correction, decompensation, disc, L3, lower instrumented vertebra, outcomes, posterior fusion, sagittal balance, wedging. Level of Evidence: 4 Spine 2020;45:E1416–E1420 D etermination of lower instrumented vertebra (LIV) in adolescent idiopathic scoliosis (AIS) surgery still remains a relevant challenge. Sparing the distal fusion levels is beneficial for better postoperative mobility, and certainly enhances overall clinical outcome; nonethe- less, late distal decompensation is of concern. For instance, L4 has been often chosen as LIV in posterior fusion for those patients with structural lumbar curvature to achieve better correction, but if routinely applied to all AIS patients this surgical strategy would increase the biomechanical stress on just two residual mobile segments at L4/5 and L5/S1. As such, loss of mobility of lower back can be significant, as well as the concerns of early distal degeneration. These issues can be particularly important for AIS patients as their annual cumulative risk of long-term sequelae is necessarily greater than older patients with degenerative scoliosis. 1,2 On the other hand, correction techniques evolved over the years due to better instrument constructs and more sophisticated surgical skills, so that L3 has been widely advocated as LIV; this strategy has been supported by the generally very good short-term outcomes. 1,3,4 However, suboptimal correction stopping at L3 can be even more harmful to the distal From the a Division of Orthopaedics, Hospital for Sick Children, Toronto, Ontario, Canada; b Division of Orthopaedic Surgery, Toronto Western Hospital, Toronto, Canada; and c Department of Orthopaedic Surgery, the University of Tokyo, Tokyo, Japan. Acknowledgment date: December 10, 2019. First revision date: January 31, 2020. Acceptance date: May 13, 2020. The manuscript submitted does not contain information about medical device(s)/drug(s). The Nakatomi Foundation funds were received in support of this work. Relevant financial activities outside the submitted work: consultancy, grants, stocks, payment for lecture, travel/accommodations/meeting expenses. Address correspondence and reprint requests to So Kato, MD, PhD, Depart- ment of Orthopaedic Surgery, University of Tokyo, 7-3-1 Hongo, Bunkyo- ku, Tokyo 1138655, Japan; E-mail: skatou-tky@umin.net DOI: 10.1097/BRS.0000000000003616 E1416 www.spinejournal.com November 2020 SPINE Volume 45, Number 21, pp E1416–E1420 ß 2020 Wolters Kluwer Health, Inc. All rights reserved. DEFORMITY