Anterior vertebral body tethering for idiopathic scoliosis: how well does the tether hold up?

Purpose: Durability of outcomes following vertebral body tethering (VBT) is a concern and may be impacted by tether breakage (TB), which has been unstudied in a large cohort. We characterized TB rates and their impact on clinical outcomes in the largest single-surgeon series to date. Methods: Inclusion criteria were VBT patients with AIS, major Cobb angle ≤ 75°, and minimum 2-year follow-up (FU). TBs were identified on 1- and 2-year FU X-rays. TB rates between single-cord and double-cord tethers were evaluated using two-proportion z test. Curve correction rates and SRS-22 scores between patients with and without TB at 2 years were evaluated using Mann–Whitney U test. Results: 69 patients were included. By 2-year FU, 18 (27%) had experienced TB. TB primarily occurred in major (70%) versus minor curves and thoracolumbar tethers (75%) versus thoracic. TB rates between thoracolumbar single (32%) and double-cord tethers (30%) were not significantly different (p = 0.88). Mean major curve correction at 2-year FU was lower (p = 0.02) in patients with major curve TB (48° to 24°, 50%) versus those without (53°–21°, 60%). 2 patients (3%) required reoperation, 1 due to foraminal encroachment from a screw tip and 1 for curve progression with TB. Conclusion: TB rate was 27% at 2 years following VBT. Broken major curve tethers are associated with minor loss of correction that may not be clinically significant. TB rates are higher for thoracolumbar curvatures and double cords may not be protective against TB. Further study of long-term TB rates is imperative.