The magnitude of postoperative anterior vertebral body tethering scoliosis correction as measured by inter-screw angulation is dependent on the remaining growth potential at the time of surgery

Background: To assess how skeletal maturity at the time of anterior vertebral body tether (VBT) surgery affects progressive scoliosis correction, we compared the segmental rate of subsequent postoperative scoliosis correction, as measured by inter-screw angulation, based on preoperative Sanders score. Methods: Thoracic idiopathic scoliosis patients with minimum 2 years follow-up after VBT (2012–2018) had coronal segmental inter-screw angulation measured for each tethered level at first erect (FE) and every 6mo up to ≥ 24mo. Change in screw angulation between 6mo intervals was calculated. Generalized linear mixed models (GLMM) and generalized estimating equation (GEE) were used to evaluate changes in screw angulation over time and for each preoperative Sanders stage. Results: There were 144 total cases—85% female, 78% Lenke 1 curve type, and mean age of 12 ± 2 years. Sanders scores ranged from 1–7 (60% ranged from 2-3B). Preoperative thoracic curve averaged 49 ± 10° (range 30–74°), which corrected to 28 ± 8° (range 8–54°) on the FE radiograph and 28 ± 12° (range 6–64°) at latest follow-up. Follow-up duration averaged 32 ± 5mo. GLMM showed cumulative screw angle change significantly differed for Sanders 1 at all time points, Sanders 2 up to 18mo, Sanders 3A up to 12mo, Sanders 3B differed between FE-6mo and 6-12mo only, Sanders 4 up to 12mo, Sanders 5–7 showed significant change between FE-6mo and 6–12mo only. The GEE model showed that Sanders 1 and 2 do not differ significantly but have greater overall change in average screw angulation than all other Sanders stages (p < 0.05). Sanders 3A has significantly more change than 3B, 4, 5, 6, and 7 (p < 0.05). Sanders 3B, 4, and 5 have significantly more overall change than Sanders 6 and 7 (p < 0.05). Sanders 6 and 7 do not significantly differ (p > 0.05). Conclusion: There was considerable variation in the progressive post-implantation thoracic curve correction following VBT based on initial skeletal maturity. The cumulative effect based on preoperative Sanders score may help guide surgical timing and set initial correction goals.