• Tomohiro Banno, Yu Yamato, Hiroki Oba, Tetsuro Ohba, Tomohiko Hasegawa, Go Yoshida, Hideyuki Arima, Shin Oe, Yuki Mihara, Hiroki Ushirozako, Jun Takahashi, Hirotaka Haro, and Yukihiro Matsuyama.
• Department of Orthopaedic Surgery, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka, Japan.
• Spine. 2021 Aug 15; 46 (16): E878E887E878-E887.

Study DesignRetrospective multicenter study.ObjectiveThis study aimed to investigate the incidence and risk factors of subjacent disc wedging (SDW) in adolescent idiopathic scoliosis (AIS) patients with Lenke type 5 curve.Summary Of Background DataSDW is frequently observed after surgery; however, data about its mechanism and relations with outcome are limited.MethodsData of 59 patients with AIS with Lenke type 5 curves who underwent posterior spinal fusion to L3 as the lowest instrumented vertebra (LIV) were retrospectively analyzed. The subjacent disc angle (SDA) was defined as the angle between L3 (LIV) and L4. SDW was defined as the absolute value of SDA of 10° or higher 2 years postoperatively. The incidence of SDW was investigated between nonselective and selective thoracolumbar/lumbar (TL/L) fusion group. In the selective group, patients with and without SDW were compared.ResultsAmong 59 patients, 11 had nonselective and 48 had selective fusion. No patients in the nonselective group showed SDW versus 13 patients in the selective group (27%) showed SDW. In the selective group, patients with SDW showed significantly greater main thoracic curve, apical vertebral translation of the main thoracic curve, upper instrumented vertebra tilt, LIV tilt, and SDA 2 years postoperatively, whereas no differences were found in the coronal balance or clinical outcome. Multivariate analysis revealed preoperative T curve and SDA as predictors of SDW occurrence. T curve greater than 30° and SDA greater than 0° were calculated as cutoff values based on the receiver operating characteristic curve.ConclusionSDW is sometimes seen in Lenke type 5 patients with AIS who underwent selective TL/L fusion. SDW seemed to occur as a compensation mechanism for progressing deformity of unfused segments (thoracic curve and residual lumbar curve) to maintain coronal alignment. Preoperative T curve > 30° and SDA > 0° (lower-end vertebra as L4) were determined as risk factors for SDW occurrence.Level of Evidence: 3.Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.

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