Study DesignRetrospective, multicenter.ObjectivesThis study aims to evaluate the immediate postoperative effect of, and define indications for, an anterior release (discectomy) in large AIS curves utilizing 3D deformity analysis.MethodsA multicenter registry was queried for AIS patients with main thoracic curves ≥70° treated with either anterior/posterior (AP) or posterior-only surgery and biplanar stereoradiographic pre-operative and first-erect (FE) postoperative images. Standard 2D radiographic and 3D parameters were analyzed using custom MATLAB software. 3D thoracic kyphosis (3DTK) was calculated by removing the error induced by axial rotation and coronal deformity.Results109 patients were included, 21 AP and 88 posterior-only. The AP group had larger (89° vs 76°,