Underweight patients are at just as much risk as super morbidly obese patients when undergoing anterior cervical spine surgery

BACKGROUND CONTEXT: Past studies have focused on the association of high body mass index (BMI) on spine surgery outcomes. These investigations have reported mixed conclusions, possible due to insufficient power, poor controlling of confounding variables, and inconsistent defi- nitions of BMI categories (e.g. underweight, overweight, and obese). Few studies have considered outcomes of patients with low BMI. PURPOSE: To analyze how anterior cervical spine surgery outcomes track with World Health Organization categories of BMI to better assess where along the BMI spectrum patients are at risk for adverse perioperative outcomes. DESIGN/SETTING: Retrospective cohort study. PATIENT SAMPLE: Patients undergoing elective anterior cervical spine surgery were abstracted from the 2005 to 2016 American College of Surgeons National Surgical Quality Improvement Pro- gram database. OUTCOME MEASURES: Thirty-day adverse events, hospital readmissions, postoperative infec- tions, and mortality. METHODS: Patients undergoing anterior cervical spine procedures (anterior cervical discectomy and fusion, anterior cervical corpectomy, cervical arthroplasty) were identified in the 2005 to 2016 National Surgical Quality Improvement Program database. Patients were then aggregated into modified World Health Organization categories of BMI. Odds ratios of adverse outcomes, normal- ized to average risk of normal weight subjects (BMI 18.5-24.9 kg/m(2) ), were calculated. Multivari- ate analyses were then performed on aggregated adverse outcome categories controlling for demographics (age, sex, functional status) and overall health as measured by the American Society of Anesthesiologists classification. RESULTS: In total, 51,149 anterior cervical surgery patients met inclusion criteria. Multivariate analyses revealed the odds of any adverse event to be significantly elevated for underweight and super morbidly obese patients (Odds Ratios [OR] of 1.62 and 1.55, respectively). Additionally, underweight patients had elevated odds of serious adverse events (OR=1.74) and postoperative infections (OR=1.75) and super morbidly obese patients had elevated odds of minor adverse events (OR=1.72). Relative to normal BMI patients, there was no significant elevation for any adverse out- comes for any of the other overweight/obese categories, in fact some had reduced odds of various adverse outcomes.