Weight loss makes the difference: perioperative outcomes following posterior lumbar fusion in patients with and without weight loss following bariatric surgery

Morbid obesity (MO) has been associated with increased risk of adverse events following procedures such as posterior lumbar fusion (PLF). While preemptive bariatric surgery (BS) has been considered for those with MO (body mass index [BMI] ≥35 kg/m2), not all undergoing such intervention have significant weight loss, and the impact of BS has been shown to correlate with weight loss after different related procedures.To examine outcomes following isolated single level PLF among patients with history of BS who subsequently did and did not transition out of the morbidly obese category.Retrospective case-control study.The PearlDiver 2010-Q1 2020 MSpine database was used to identify adult patients undergoing elective isolated PLF. Patients were excluded if they had a history of infection, neoplasm, or trauma in the 90-days prior to their PLF and if they were not active in the database for at least 90 days following their surgery. Three sub-cohorts were defined: 1) MO controls without a history of BS (-BS+MO), 2) patients with prior BS procedure who remained MO (+BS+MO), and 3) patients with prior BS who were no longer MO at the time of PLF (+BS-MO). Matched 1:1:1 populations were created for these three sub-cohorts based on age, sex and Elixhauser Comorbidity Index (ECI).Ninety-day adverse events and readmission rates were assessed and compared between the three sub-cohorts (-BS+MO, +BS+MO, +BS-MO).Univariable analyses and multivariable logistic regression were performed on the matched population to compare 90-day adverse events and readmission rates controlling for age, sex, and ECI.The current study identified PLF patients who were MO at the time of surgery but did not have a history of BS (-BS+MO, n=34,236), those who had BS and remained MO (+BS+MO, n=564), and those who had MS and were no longer MO (+BS-MO, n=209 which was only 27% of those who had BS). On multivariable analysis of the matched populations, those that had BS but remained MO (+BS+MO) were not at reduced odds of 90-day adverse events. However, those that had BS and were no longer MO (+BS-MO) were at reduced odds of 90-day any, severe, and minor adverse events (OR 0.41, 0.51, and 0.37, respectively with p<0.05 for all).Only 27% of those with a history of BS prior to PLF transitioned out of the MO category. Compared to those who were morbidly obese without BS, those who had BS were only at reduced risk of 90-day adverse events if they actually lost weight sufficient to drop out of morbidly obesity. These findings should be taken into account when counseling patients and interpreting prior studies.