Body mass index affects outcomes after vertebral body tethering surgery

Purpose: To compare the outcomes of anterior Vertebral Body Tethering (AVBT) surgery between overweight and non-overweight patients.

Methods: AIS/JIS patients with AVBT with 2-year follow-up from a multi-center pediatric spine database were evaluated pre-operatively, 1st post-operative erect, and 2 years post-operatively. ANOVA was used to compare 3 categories of BMI with significance as per Tukey-Kramer HSD post hoc test. Risk of scoliosis progression was analysed with Mid-P exact test.

Results: 121 patients (51 underweight, 58 normal, 12 overweight; mean age 12.5 ± 1.6 yr; BMI 18.8 ± 4.6 kg/m²) were identified. Comparing underweight, normal, and overweight groups: mean pre-operative age (13 yr, 13 yr, 12 yr), scoliosis (52°, 50°, 52°), pre-operative kyphosis (29°, 28°, 33°), peri-operative scoliosis correction (44%, 42%, 46%), and complications by 2-year follow-up (23%, 24%, 17%) were similar between groups. There was one broken tether in each of the underweight and normal weight groups. Change in percent scoliosis correction from 1st erect to 2-year post-operative (i.e., growth modulation phase) was not significantly different between groups; however, the risk ratio for scoliosis progression during this period was 4.74 (1.02-22.02; p = 0.04) for overweight patients.

Conclusion: Our findings demonstrate that, as compared to normal weight and underweight patients, overweight patients did not have a statistically significant difference in intra-operative scoliosis correction or in risk of experiencing complication; however, overweight patients had a risk ratio of 4.74 for progression of scoliosis during the growth modulation phase of treatment from first erect radiographs to minimum 2-year follow-up.

Level of evidence: III.