Study design:

Retrospective cohort study.

Objective:

To investigate the relationship between body mass index (BMI), spine flexibility index (FI), and their combined effects on adolescent idiopathic scoliosis (AIS) surgical outcomes.

Background:

BMI and FI are two factors considered during pre-surgical planning for AIS correction, but there is sparse research about their relationship. We hypothesize that AIS patients with increased BMI may be associated with decreased FI – a combination which could lead to worsened surgical outcomes.

Methods:

AIS patients ages 11-19 at surgery, who underwent posterior fusion at a single-center from 2011-2017, were reviewed. Patients without proper radiographs to assess FI, or a previous spine surgical history, were excluded. FI was categorized as stiff (FI<50) or flexible (FI≥50), and patients were separated by major curve region. BMI was categorized as underweight (<5th percentile), healthy-weight (5th-85th percentile), overweight (85th-95th percentile), or obese (>95th percentile). Regression analysis was conducted to test BMI and FI’s effects on intraoperative, immediate postoperative, and two-year postoperative outcomes.

Results:

543 patients (82% female), with an average age of 14.9 years, were included. 346 patients had available two-year data. A 10% increase in BMI was associated with a 1.3% decrease in FI for patients with major thoracolumbar/lumbar curves (P=0.01). Obese patients were most likely to have a postoperative complication (P=0.003) or two-year complication (P=0.04). Revision surgery occurred after 58% of postoperative complications (15/26) and 80% of two-year complications (4/5). FI was negatively associated with initial curve magnitude (P<0.001), operative time (P=0.02), and blood loss (P=0.02). Overweight patients with flexible curves were 10.0 times more likely to sustain a postoperative complication than healthy-weight patients with stiff curves (P=0.001).

Conclusion:

Elevated BMI was associated with decreased FI in patients with major thoracolumbar/lumbar curves. Patients with a high BMI and high FI were associated with the greatest risk of postoperative complication.