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

Abstract 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 definitions of BMI categories (e.g. underweight, overweight, 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 (WHO) categories of BMI to better assess where along the BMI spectrum patients are at risk for adverse perioperative outcomes. Study Design/Setting Retrospective cohort study Patient Sample Patients undergoing elective anterior cervical spine surgery were abstracted from the 2005-2016 American College of Surgeons National Surgical Quality Improvement Program (NSQIP) database. Outcome Measures Thirty-day adverse events, hospital readmissions, post-operative infections, and mortality. Methods Patients undergoing anterior cervical spine procedures (anterior cervical discectomy and fusion, anterior cervical corpectomy, cervical arthroplasty) were identified in the 2005-2016 NSQIP database. Patients were then aggregated into modified WHO categories of BMI. Odds ratios of adverse outcomes, normalized to average risk of normal weight subjects (BMI 18.5-24.9 kg/m2), were calculated. Multivariate 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 (ASA) 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 outcomes for any of the other overweight/obese categories, in fact some had reduced odds of various adverse outcomes. Conclusions Underweight and super morbidly obese patients have the greatest odds of adverse outcomes after anterior cervical spine surgery. The current study identifies underweight patients as an at-risk population that has previously not received significant focus. Physicians and healthcare systems should give additional consideration to this population, as they often already do for those at the other end of the BMI spectrum.