Redefining Success and Characterizing Midterm Growth Modulation: Analysis of Radiographic Outcomes in 2 Years Following Vertebral Body Tethering.

Background: Vertebral body tethering (VBT) offers fusionless correction for idiopathic scoliosis, yet midterm growth modulation remains poorly characterized. This study established a clinically relevant success criterion and characterized growth modulation kinetics with associated predictors. Methods: This multicenter prospective study enrolled patients with idiopathic scoliosis with Sanders stage ≤7A, preoperative fulcrum-bending flexibility rate ≥50%, and ≥2-year follow-up after VBT. Parameters were collected before surgery and at 7 postoperative time points. Two-year success was defined as Cobb angle <35° (group 1) and correction rate (CR) ≥50% without overcorrection (Group 2). Group 3 included cases with an instrumented Cobb angle <35° but CR <50%. Curves were further classified as undercorrection (CR <50%), overcorrection (negative curve), and short-term clinical success (same as group 2) at 2 years postoperatively. Results: ), and higher immediate CR (84.9%). Conclusion: VBT effectively corrects coronal and axial deformity. A short-term success criterion based on a Cobb angle CR ≥ 50% without overcorrection better reflects a favorable biological response than the <35° benchmark at 2 years. Skeletally immature, lean patients with high flexibility and continued correction beyond 6 months may signal overcorrection risk. Level of Evidence: Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.