Preoperative Fulcrum Flexibility >80% Is Associated With Clinical Success in Vertebral Body Tethering

Study designSingle-centre prospective study.ObjectivesOur study aims to investigate the relationship between preoperative and intraoperative factors with VBT surgical outcomes.MethodsThis is a single-centre prospective study involving consecutive VBT patients. All patients included were followed up for >2 years postoperatively. Primary outcomes were changes in radiographic parameters from pre-operative to immediate post-operative and between subsequent follow-ups. Secondary outcomes were the relationships between preoperative and intraoperative factors with coronal correction rate. Preoperative factors included fulcrum flexibility and skeletal maturity. Intraoperative factors were intraoperative tensioning, screw positioning, screw length and immediate coronal correction. Presence of growth modulation was defined as >5° further curve correction postoperatively, while postoperative clinical success was defined as <30° coronal curve magnitude and avoidance of revision surgery.ResultsForty-one patients (35 females, 6 males) with 53 curves were included. Preoperative curve magnitude was 49.0 ± 7.4° and improved to 17.4 ± 8.0° immediately post-op (P < 0.001), with mean correction rate at 64.6 ± 15.4%. Coronal correction rate was persistently maintained at 62.1 ± 29.0% at 2-year. Preoperative flexibility correlated with correction rate at immediate post-operatively up to 18-month (correlation coefficient (r) = 0.768 to 0.933; P = 0.002 to P = 0.044). Strength of intraoperative tensioning at upper and apical curve segments was negatively associated with correction rate up till 9-month (r = -0.409 to -0.620) but could be explained by decision to tension more in less flexible curves. Preoperative fulcrum flexibility >79.8% (i.e. 80%) predicted postoperative clinical success (AUC 0.760; P < 0.001).ConclusionVBT improved curve magnitude and shoulder imbalance in scoliosis with progressive spinal growth. Flexible curves were associated with persistent coronal correction, while flexibility above 80% increases chance of clinical success with minimal risk of further progression. Growth modulation was associated with skeletal immaturity.