The Obesity Paradox: A Nonlinear Relationship Between 30-Day Postoperative Complications and Body Mass Index After Total Shoulder Arthroplasty

BACKGROUND: An inverse relationship coined the "obesity paradox" has been propositioned, in which body mass index (BMI) may be contradictorily protective in patients undergoing surgery or treatment of chronic disease. This study sought to investigate the BMI associated with the lowest rate of medical complications after total shoulder arthroplasty (TSA). METHODS: The American College of Surgeons National Surgical Quality Improvement Project database was queried to identify adults who underwent elective primary TSA between January 2012 and December 2020. Thirty-day postoperative medical complications were extracted, which included death, readmission, pneumonia, pulmonary embolism, renal failure, and cardiac arrest, among others. BMI was classified into five categories (underweight [BMI <18.5 kg/m 2 ], normal weight [BMI ≥18.5 and <25 kg/m 2 ], overweight [BMI ≥25 and <30 kg/m 2 ], obese [BMI ≥30 and <40 kg/m 2 ], and morbidly obese [BMI ≥40 kg/m 2 ]). We examined the risk of any 30-day postoperative complications and BMI categorically and on a continuous basis using multivariable logistic regression controlling for age, sex, procedure year, and comorbidities. RESULTS: Of the 31,755 TSAs, 84% were White, 56% were female, and the average age of patients was 69.2 ± 9.3 years. Thirty-day postoperative medical complications occurred in 4.53% (n = 1,440). When assessed on a continuous basis, the lowest risk was in patients with a BMI between 30 and 35 kg/m 2 . Underweight individuals (BMI <18.5 kg/m 2 ) had the highest postoperative complication rates overall. The probability of medical complications increased with age and was greater for female patients. CONCLUSION: The relationship between BMI and complication risk in TSA is nonlinear. A BMI between 30 and 35 kg/m 2 was associated with the lowest risk of medical complications after TSA, and BMI<18.5 kg/m 2 had the highest risk overall, indicating some protective aspects of BMI against 30-day medical complications. Thus, obesity alone should not preclude patients from TSA eligibility, rather surgical candidacy should be evaluated in the context of patients' overall health and likelihood of benefit from TSA. LEVEL OF EVIDENCE: III, Retrospective Comparative Study.