Body mass index predicts risk of complications in lumbar spine surgery based on surgical invasiveness

Background Context

Obesity as a comorbidity in spine pathology may increase the risk of complications following surgical treatment. The body mass index (BMI) threshold at which obesity becomes clinically relevant, and the exact nature of that effect, remains poorly understood.

Purpose

Identify the BMI that independently predicts risk of postoperative complications following lumbar spine surgery.

Study Design/Setting

Retrospective review of the National Surgery Quality Improvement Program (NSQIP) years 2011–2013.

Patient Sample

A total of 31,763 patients were undergoing arthrodesis, discectomy, laminectomy, laminoplasty, corpectomy, or osteotomy of the lumbar spine.

Outcome Measures

Complication rates.

Methods

The patient sample was categorized preoperatively by BMI according to the World Health Organization stratification: underweight (BMI <18.5), normal overweight (BMI 20.0–29.9), obesity class 1 (BMI 30.0–34.9), 2 (BMI 35.0–39.9), and 3 (BMI≥40). Patients were dichotomized based on their position above or below the 75th surgical invasiveness index (SII) percentile cutoff into low-SII and high-SII. Differences in complication rates in BMI groups were analyzed by Bonferroni analysis of variance (ANOVA) method. Multivariate binary logistic regression evaluated relationship between BMI and complication categories in all patients and in high-SII and low-SII surgeries.

Results

Controlling for baseline difference in SII, Charlson Comorbidity Index (CCI) score, diabetes, hypertension, and smoking, complications significantly increased at a BMI of 35?kg/m². The odds ratios for any complication (odds ratio [OR] [95% confidence interval {CI}]; obesity 2: 1.218 [1.020–1.455]; obesity 3: 1.742 [1.439–2.110]), infection (obesity 2: 1.335 [1.110–1.605]; obesity 3: 1.685 [1.372–2.069]), and surgical complication (obesity 2: 1.622 [1.250–2.104]; obesity 3: 2.798 [2.154–3.634]) were significantly higher in obesity classes 2 and 3 relative to the normal-overweight cohort (all p<.05).

Conclusion

There is a significant increase in complications, specifically infection and surgical complications, in patients with BMI≥35 following lumbar spine surgery, with that rate further increasing with BMI≥40.