How Does Body Mass Index Influence Outcomes in Patients After Lumbar Fusion?

Abstract

STUDY DESIGN: Retrospective study. OBJECTIVE: The purpose of the present study is to determine how body mass index (BMI) affects patient-reported outcome measurements (PROMs) after lumbar fusions. SUMMARY OF BACKGROUND DATA: Although greater preoperative BMI is known to increase the rates of adverse events after surgery, there is a paucity of literature assessing the influence of BMI on PROMs after lumbar fusion. METHODS: Patients undergoing lumbar fusion surgery between 1 and 3 levels were retrospectively identified. PROMs analyzed were the Short Form-12 Physical Component Score, Mental Component Score, Oswestry Disability Index (ODI), and Visual Analog Scale Back and Leg pain scores. Patients were divided into groups based on preoperative BMI: class 1, BMI <25.0; class 2, BMI 25.0 to 29.9; class 3, BMI 30.0 to 34.9; and class 4, BMI ≥35.0. Absolute PROM scores, the recovery ratio, and the percentage of patients achieving minimum clinically important difference between groups were compared. RESULTS: A total of 54 (14.8%) patients in class 1, 140 (38.2%) in class 2, 109 (29.8%) in class 3, and 63 (17.2%) in class 4 were included. All patients improved after surgery across all outcome measures (P < 0.001) except for class 4 patients, who did not improve in terms of Short Form-12 Mental Component Score scores after surgery (P = 0.276). Preoperative Short Form-12 Physical Component Score (P = 0.002) and Oswestry Disability Index (P < 0.0001) scores were significantly different between BMI groups-with class 4 having worse disability than class 1 and 2. BMI was not a significant predictor for any outcome domain. Overall 30- and 90-day readmission rates were similar between groups, with a higher revision rate in the class 4 group (P = 0.036), due to a higher incidence of postoperative surgical site infections (P = 0.014). CONCLUSION: All patients undergoing short-segment lumbar fusion for degenerative disease improved to a similar degree with respect to PROMs. Those in the highest class of obesity (BMI ≥35.0) were, however, at a greater risk for postoperative surgical site infection. LEVEL OF EVIDENCE: 3.