• Graham Mulvaney, Olivia M Rice, Vincent Rossi, David Peters, Mark Smith, Joshua Patt, Deborah Pfortmiller, Anthony L Asher, Paul Kim, Joe Bernard, and Matthew McGirt.
• Carolina Neurosurgery & Spine Associates, Charlotte, North Carolina.
• Neurosurgery. 2021 Jan 13; 88 (2): 285-294.

BackgroundElevated body mass index (BMI) is a well-known risk factor for surgical complications in lumbar surgery. However, its effect on surgical effectiveness independent of surgical complications is unclear.ObjectiveTo determine increasing BMI's effect on functional outcomes following lumbar fusion surgery, independent of surgical complications.MethodsWe retrospectively analyzed a prospectively built, patient-reported, quality of life registry representing 75 hospital systems. We evaluated 1- to 3-level elective lumbar fusions. Patients who experienced surgical complications were excluded. A stepwise multivariate regression model assessed factors independently associated with 1-yr Oswestry Disability Index (ODI), preop to 1-yr ODI change, and achievement of minimal clinically important difference (MCID).ResultsA total of 8171 patients met inclusion criteria: 2435 with class I obesity (BMI 30-35 kg/m2), 1328 with class II (35-40 kg/m2), and 760 with class III (≥40 kg/m2). Increasing BMI was independently associated with worse 12-mo ODI (t = 8.005, P < .001) and decreased likelihood of achieving MCID (odds ratio [OR] = 0.977, P < .001). One year after surgery, mean ODI, ODI change, and percentage achieving MCID worsened with class I, class II, and class III vs nonobese cohorts (P < .001) in stepwise fashion.ConclusionIncreasing BMI is associated with decreased effectiveness of 1- to 3-level elective lumbar fusion, despite absence of surgical complications. BMI ≥ 30 kg/m2 is, therefore, a risk factor for both surgical complication and reduced benefit from lumbar fusion.Copyright © 2020 by the Congress of Neurological Surgeons.

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