Sagittal alignment outcomes following two-row vertebral body tethering versus posterior spinal fusion in adolescent idiopathic scoliosis: a multicenter two-year study.

Abstract

Multicenter retrospective cohort study. To compare 2-year sagittal alignment outcomes between two-row vertebral body tethering (2RVBT) and posterior spinal fusion (PSF) in adolescent idiopathic scoliosis (AIS). PSF remains the gold standard for AIS correction; however, concerns regarding motion loss and adjacent segment disease have encouraged development of fusionless techniques such as vertebral body tethering (VBT). While VBT has demonstrated promising coronal correction, evidence regarding its effects on sagittal alignment is limited. Ninety-nine AIS patients (49 2RVBT, 50 PSF) with ≥ 2-year follow-up were analyzed. Radiographic parameters included sagittal vertical axis (SVA), cervical sagittal vertical axis (cSVA), cervical lordosis (CL), pelvic tilt (PT), L4-S1 lordosis, T1 pelvic angle (TPA), and pelvic incidence-lumbar lordosis mismatch (PI-LL). The minimal clinically important difference (MCID) was prespecified as 5 mm for sagittal axis and 10° for lordosis, with pediatric thresholds of 3 mm and 5° based on AIS literature. Institutional Review Board approval was obtained at all participating centers. Inclusion criteria were AIS diagnosis, age ≤ 16 years at surgery, lumbar instrumentation, and ≥ 2-year follow-up. Exclusion criteria included neuromuscular/syndromic scoliosis and prior spinal surgery. 2RVBT patients were younger, more skeletally immature (Risser 1.6 ± 0.8 vs. 2.6 ± 1.8, p = 0.001), and more frequently female (97% vs. 84%, p = 0.048). At baseline, sagittal parameters differed between groups, with lower SVA, cervical lordosis, and L4 to S1 lordosis, and higher cSVA in the 2RVBT group. At 2 years, 2RVBT maintained greater L4-S1 lordosis (36.0° vs. 18.3°, p = 0.001) and cSVA (3.4 mm vs. - 3.7 mm, p = 0.001), with lower CL (-4.3° vs. 7.0°, p = 0.001). Between-group changes from baseline to 2 years did not exceed MCID thresholds. Findings were unchanged in a Risser matched sensitivity analysis, with balanced baseline demographics and sagittal parameters and no between group changes exceeding prespecified MCID thresholds. 2RVBT and PSF produce comparable sagittal alignment changes at 2 years, with no between-group differences in change from baseline exceeding MCID thresholds. 2RVBT preserves motion without compromising sagittal balance in skeletally immature AIS patients.