Underweight Patients Are the Greatest Risk Body Mass Index Group for 30-Day Perioperative Adverse Events After Total Shoulder Arthroplasty.

INTRODUCTION Existing literature investigating the correlation of body mass index (BMI) with surgical complications has focused on those with elevated BMI. These investigations have reported mixed conclusions, possible because of insufficient power, poor controlling of confounding variables, and inconsistent definitions of BMI categories (eg, underweight, overweight, and varying classifications of obese). Few studies have considered complications of patients with low BMI. The aim of the current study was to analyze the spectrum of categories for BMI with 30-day perioperative adverse events after primary total shoulder arthroplasty (TSA) to better assess where along the BMI spectrum patients are at risk for complications. METHODS Patients undergoing elective TSA were abstracted from the National Surgical Quality Improvement Program (NSQIP) databases from 2005 to 2016. Patients were then aggregated into BMI categories, and 30-day adverse events were normalized to average risk of normal-weight subjects (BMI 18.5 to 24.9 kg/m). Risk-adjusted multivariate regressions were performed, controlling for demographic variables and overall health. RESULTS In total, 15,717 patients met the inclusion criteria. Underweight TSA patients (BMI < 18.5 kg/m) had the greatest odds for multiple perioperative adverse events compared with any other BMI category. By multivariate analysis, underweight patients were more likely to experience any adverse event (odds ratio [OR] = 2.22, P = 0.034), serious adverse events (OR = 3.18, P = 0.004), or have postoperative infections (OR = 2.77, P = 0.012) within 30 days when compared with normal-weight patients. No significant difference was observed in these complications for elevated BMI categories when compared with normal-weight patients. CONCLUSIONS Only underweight TSA patients were found to have higher rates of 30-day perioperative adverse events than normal BMI patients, unlike any overweight/obese category including the super morbidly obese. Underweight TSA patients were thus identified as an at-risk subpopulation of TSA patients who had not previously been described. Physicians and healthcare systems should give additional consideration to this fragile cohort because they often already do for those at the other end of the BMI spectrum. LEVEL OF EVIDENCE III.