Reducing Uncertainty in Anterior Vertebral Body Tethering: Predicting Postoperative Curvature With Fulcrum Bending Radiographs.

Abstract

Retrospective Cohort Study. Mid-term Anterior Vertebral Body Tethering (AVBT) results demonstrate an acceptable degree of clinical success, yet the revision rate remains notably higher than fusion. Fulcrum-bending radiographs have previously been shown to more reliably predict radiological outcomes in Adolescent Idiopathic Scoliosis (AIS) as compared to supine-lateral bending radiographs. This study aims to discern how Fulcrum Flexibility Rate (FFR) correlates with Correction Rate (CR) and establish whether this can reliably predict residual deformity following AVBT surgery. A review of 38 consecutive AIS patients undergoing thoracic AVBT between 2015 - 2020 was performed. Preoperative (standing and fulcrum-bending) and postoperative (first-erect) radiographs were evaluated for curve magnitude using the Cobb-method. The FFR, CR and Fulcrum Bending Correction Index (FBCI) were calculated. Patients were also percentile-ranked according to their FFR and dichotomized into flexible and rigid cohorts for comparison. Student t-test, Pearson correlation and linear stepwise regression was applied. AVBT resulted in a significant improvement in the major Cobb angle (Preoperative: 50.9±7.5° vs Postoperative: 19.9±9.4°; <i>P</i> < .0001) with a mean FBCI of 98.0%. Bivariate correlation revealed a moderate relationship between fulcrum-bending and first-erect Cobb angle (r = .5306, <i>P</i> = .0006). Linear regression demonstrated a predictive relationship between fulcrum-bending and first-erect Cobb using the equation 'Postoperative Cobb = 7.5 + .65(Fulcrum-bending Cobb).' This is the first study to demonstrate the ability of fulcrum-bending radiographs to predict early radiographic outcomes following AVBT, 'timepoint-zero' for the growth modulation process.