Association Between Nonsurgical Weight Loss from BMI>40 to BMI<40 and Complications and Readmissions following Total Hip Arthroplasty.

BACKGROUND: Elevated body mass index (BMI) is a risk factor for adverse outcomes following total hip arthroplasty (THA). It is unknown if preoperative weight loss to a BMI under 40kg/m2 is associated with adverse outcomes. METHODS: We retrospectively reviewed elective, primary THA performed at an academic center from 2015-2019. Patients were split into groups based on their BMI trajectory prior to THA: BMI consistently <40 ("BMI<40"); BMI >40 at the time of surgery ("BMI>40"); and BMI >40 within 2 years preoperatively, but <40 at the time of surgery ("Weight Loss"). Length of stay (LOS), 30-day readmissions, and complications as defined by CMS were compared between groups using parsimonious regression models and Fisher's exact testing. Adjusted analyses controlled for sex, age, and ASA class. RESULTS: 1,589 subjects were included (BMI<40: 1387, BMI>40: 96, Weight Loss: 106). The rate of complications in each group was 3.5%, 6.3%, 8.5% and the rate of 30-day readmissions was 3.0%, 4.2%, and 7.5%, respectively. Compared to the BMI<40 group, the weight loss group had a significantly higher risk of 30-day readmission (OR=2.70, 95% CI 1.19-6.17, p=0.02), higher risk of any complication (OR=2.47, 95% CI 1.09-5.59, p=0.03), higher risk of mechanical complications (OR 3.07, 95% CI 1.14-8.25, p=0.03), and longer median LOS (16% increase, p=0.002). The BMI>40 group had increased median LOS (10% increase, p=0.03), but no difference in readmission or complications (p>0.05) compared to BMI<40. CONCLUSION: Weight loss from BMI>40 to BMI<40 prior to THA was associated with increased risk of readmission and complications compared to BMI<40, whereas BMI>40 wasn't.