Rate of Scoliosis Correction After Anterior Spinal Growth Tethering for Idiopathic Scoliosis

Background: The purpose of the present study was to evaluate associations between changes in segmental vertebral coronal angulation (screw angulation) and overall height after anterior spinal growth tethering for the treatment of idiopathic scoliosis and to compare the rates of coronal angulation change using the preoperative Sanders stage. Methods: Patients with idiopathic scoliosis who underwent anterior spinal growth tethering between 2012 and 2016 and had >= 2 years of follow-up were retrospectively studied. We calculated each segment's screw angulation rate of change (degrees/month) and each patient's height velocity (cm/month) between each of the visits (3 to 12 visits/patient) and divided the visits into 4 groups by postoperative duration (<1 year, 1 to 2 years, >2 to 3 years, >3 years). Patients were divided into 2 groups according to the preoperative Sanders stage. Generalized estimating equations and repeated-measures correlation were utilized for analyses with non-independent samples. Results: We analyzed 23 patients (16 female, 7 male) with a mean age (and standard deviation) of 12.2 +/- 1.6 years who had right thoracic idiopathic scoliosis (mean, 53 degrees +/- 8 degrees). All patients were immature at the time of surgery (Risser stage 0 or 1, Sanders stage 2 or 3). The mean duration of follow-up was 3.4 +/- 1.1 years (range, 2 to 5 years). The rate of change for each segment's screw angulation after anterior spinal growth tethering was -0.16 degrees, -0.14 degrees, -0.05 degrees, and 0.03 degrees per month (with negative values indicating a reduction in scoliosis) for <1 year, 1 to 2 years, >2 to 3 years, and >3 years, respectively (p <= 0.001), and the mean height velocity was 0.65, 0.57, 0.30, and 0.19 cm per month for <1 year, 1 to 2 years, >2 to 3 years, and >3 years, respectively (p < 0.001). Changes in screw angulation correlated with height increases after anterior spinal growth tethering (r = -0.46, p < 0.001). Scoliosis correction for patients in the Sanders stage-2 group continued for 3 years (0.23 degrees, 0.23 degrees, and 0.09 degrees per level per month for the first 3 years, respectively) and occurred at more than twice the rate for patients in the Sanders stage-3 group, for whom scoliosis correction ceased 2 years postoperatively (0.11 degrees and 0.09 degrees per level per month for the first 2 years, respectively). Conclusions: Scoliosis correction was associated with overall height changes and occurred primarily within 2 to 3 years after surgery in this cohort of largely Risser stage-0 patients. The correction rate was 2.8 degrees per segment per year for the first 2 years in the Sanders stage-2 group, compared with 1.2 degrees per segment per year for the Sanders stage-3 group. Surgical timing that considers the patient's skeletal maturity is an important factor in generating proper postoperative correction after anterior spinal growth tethering.