What Happens After a Vertebral Body Tether Break? Incidence, Location, and Progression With Five-year Follow-up

Study Design.Retrospective review. Objective.To study risk factors for anterior vertebral body tether (VBT) breakage. Summary of Background Data.VBT is used to treat adolescent idiopathic scoliosis in skeletally immature patients. However, tethers break in up to 48% of cases. Materials and Methods.We reviewed 63 patients who underwent thoracic and/or lumbar VBT with a minimum five-year follow-up. We radiographically characterized suspected tether breaks as a change in interscrew angle >5 degrees. Demographic, radiographic, and clinical risk factors for presumed VBT breaks were evaluated. Results.In confirmed VBT breaks, the average interscrew angle change was 8.1 degrees, and segmental coronal curve change was 13.6 degrees, with a high correlation (r=0.82). Our presumed VBT break cohort constituted 50 thoracic tethers, four lumbar tethers, and nine combined thoracic/lumbar tethers; the average age was 12.1 +/- 1.2 years and the mean follow-up was 73.1 +/- 11.7 months. Of 59 patients with thoracic VBTs, 12 patients (20.3%) had a total of 18 breaks. Eleven thoracic breaks (61.1%) occurred between two and five years postoperatively, and 15 (83.3%) occurred below the curve apex (P<0.05). The timing of thoracic VBT breakage moderately correlated with more distal breaks (r=0.35). Of 13 patients who underwent lumbar VBT, eight patients (61.5%) had a total of 12 presumed breaks. Six lumbar breaks (50%) occurred between one and two years postoperatively, and seven (58.3%) occurred at or distal to the apex. Age, sex, body mass index, Risser score, and curve flexibility were not associated with VBT breaks, but the association between percent curve correction and thoracic VBT breakage trended toward significance (P=0.054). Lumbar VBTs were more likely to break than thoracic VBTs (P=0.016). Seven of the patients with presumed VBT breaks (35%) underwent revision surgery. Conclusions.Lumbar VBTs broke with greater frequency than thoracic VBTs, and VBT breaks typically occurred at levels distal to the curve apex. Only 15% of all patients required revision.