Does Obesity Explain the Effect of the Metabolic Syndrome on Complications Following Elective Lumbar Fusion? A Propensity Score Matched Analysis

STUDY DESIGN: Propensity score matched retrospective cohort study. OBJECTIVES: Obesity is a major confounder in determining the independent effect of metabolic syndrome (MetS) on complications after spinal surgery. The purpose of this study is to differentiate MetS from obesity as an independent influence on perioperative outcomes after elective lumbar spine fusion. METHODS: One- to 3-level posterior spinal fusion cases were identified from the 2011-2014 American College of Surgeons’ National Surgical Quality Improvement Program. To determine the effects of MetS outside of obesity itself, patients with MetS were first compared to a no-MetS cohort and then to an obese-only no-MetS cohort. Two propensity score matches based on demographics, comorbidities, surgical complexity, and diagnosis were used to match patients in 1:1 ratios and compare outcomes. Logistic regression with propensity score adjustment was further utilized as a secondary method of reducing selection bias. RESULTS: Out of 18 605 patients that met criteria for inclusion, 1903 (10.2%) met our definition of MetS. Patients with MetS had a higher rate of wound complications (3.8% vs 2.7% obese no MetS, P = .045; vs 2.6% no MetS, P = .035), readmissions (7.4% vs 2.2% obese no MetS, P < .001; vs 4.6% no MetS, P < .001), and extended length of stay (29.1% vs 23.9% obese no MetS, P < .001; vs 23.5% no MetS, P < .001). Patients with MetS were more likely to experience a wound complication (odds ratio = 1.47, 95% confidence interval = 1.02-2.12) or readmission (odds ratio = 1.48, 95% confidence interval = 1.22-1.80). CONCLUSIONS: Even after controlling for obesity, MetS is an independent risk factor for adverse short-term outcomes. These findings have various implications for preoperative risk stratification and reduction strategies.