Study designRetrospective cohort study.Purposeto assess the efficacy and safety of Hi-PoAD technique in patients with a major thoracic curve > 90°, < 25% of flexibility and deformity spread over more than five vertebral levels.Methodsretrospective review of AIS patients with a major thoracic curve (Lenke 1–2–3) > 90°, with < 25% of flexibility and deformity spread over more than five vertebral levels. All were treated via the Hi-PoAD technique. Radiographic and clinical score data were collected pre-operatively, operatively, at 1 year, 2 years and at last follow-up (2 years minimum).Results19 patients were enrolled. A 65.0% correction rate of the main curve was achieved, from 101.9° to 35.7° (p< 0.001). The AVR reduced from 3.3 to 1.3. The C7PL/CSVL reduced from 1.5 to 0.9 cm (p= 0.013). Trunk Height increased from 31.1 to 37.0 cm (p< 0.001). At the final follow-up no significant changes, except from an improvement in C7PL/CSVL (from 0.9 cm to 0.6 cm;p= 0.017). SRS-22 increased in all patients, from 2.1 to 3.9 at 1 year of follow-up (p< 0.001). 3 patients had a transient drop of MEP and SEP during maneuver and were managed with temporary rods and a second surgery after 5 days. 2 of these 3 cases (66.7%) had a Total-Deformity Angular Ratio (T-DAR) > 25; conversely, among patients who had a one-stage procedure, only 1 (6.2%) had a T-DAR > 25 (p= 0.008).ConclusionsThe Hi-PoAD technique proved to be a valid alternative for the treatment of severe, rigid AIS involving more than 5 vertebral bodies.Study designRetrospective comparative cohort study.Level of evidenceIII.