3D Sagittal Parameters Can Guide the Indications for Anterior Release in Thoracic AIS ≥70°

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°, P < .001), less flexible (9% vs 21%, P = .001) curves, though greater percent correction (79% vs 71%, P = .003), producing similar postoperative curve magnitude (19° vs 22°, P = 0.1). The AP group had less preoperative 3DTK (-15° vs -3°, P < .001), though similar postoperative 3DTK (24° vs 20°, P = .1), nearly double the improvement (39° vs 23°, P < .001). No cases with preoperative 3DTK < -18° achieved postoperative 3DTK >25° without anterior release. Segmental data of each motion segment demonstrated anterior release led to greater change in the coronal (P < .001) and sagittal (P = .003) planes, though not axial rotation of the apical vertebra (P = .157).ConclusionIn a cohort of AIS patients with thoracic curve magnitude >70°, 3D analysis comparing anterior/posterior vs posterior-only approach demonstrated improved correction in the coronal and sagittal, but not the axial plane. If 3DTK preop was <-18° only anterior release patients achieved postoperative 3DTK >25°.Level of EvidenceIII.