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

Study Design Retrospective, multicenter. Objectives This 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. Methods A multicenter registry was queried for AIS patients with main thoracic curves >= 70 degrees 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. Results 109 patients were included, 21 AP and 88 posterior-only. The AP group had larger (89 degrees vs 76 degrees, 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 degrees vs 22 degrees, P = 0.1). The AP group had less preoperative 3DTK (-15 degrees vs -3 degrees, P < .001), though similar postoperative 3DTK (24 degrees vs 20 degrees, P = .1), nearly double the improvement (39 degrees vs 23 degrees, P < .001). No cases with preoperative 3DTK < -18 degrees achieved postoperative 3DTK >25 degrees 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). Conclusion In a cohort of AIS patients with thoracic curve magnitude >70 degrees, 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 degrees only anterior release patients achieved postoperative 3DTK >25 degrees.