The obesity paradox and orthopedic surgery

The Obesity Paradox describes the counterintuitive finding that although obesity contributes to the development of chronic conditions such as chronic kidney disease and cardiovascular disease, obesity seems to improve mortality in patients with these diseases. This paradox has also been sited in the critical care literature in regard to acute kidney injury, obesity and mortality. This study's objective is to examine the impact of obesity and post-surgical acute kidney injury on hospital length of stay and 2-year mortality after orthopedic surgery. We reviewed the electronic medical records of all adult elective orthopedic surgery patients over 2 years in a large academic hospital. The 1783 patients who met inclusion criteria were divided into obese (body mass index, BMI ≥ 30, n = 1123) and non-obese groups (BMI <30, n = 660). Demographics, medications, comorbidities, and perioperative variables were included in multivariable logistic regression analyses with acute kidney injury, length of hospital stay, and two-year mortality as primary outcomes. Outcomes were analyzed for the entire group, the obese cohort and the non-obese cohort. Acute kidney injury developed in 5% of the post-surgical orthopedic patients. Obesity increased the likelihood of developing acute kidney injury post orthopedic surgery (odds ratio [OR] = 1.82; 95% Confidence interval [CI] 1.05–3.15, P = .034). Acute kidney injury increased length of stay by 1.3 days and increased the odds of two-year mortality (OR = 2.08; 95% CI 1.03–4.22, P = .041). However, obese patients had a decreased likelihood of two-year mortality (OR = 0.53; 95% CI 0.33–0.84, P = .009). In adult orthopedic surgery patients, obesity increased the risk of acute kidney injury. Patients who developed an acute kidney injury had longer hospital stays and higher two-year mortality. Paradoxically, obesity decreased two-year mortality.