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

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