BACKGROUND: Deep venous thrombosis (DVT) and pulmonary embolus (PE) remain an important cause of morbidity and mortality after THA and TKA. Prior recommendations have advocated for more aggressive prophylaxis for patients with obesity, whereas the evidence supporting these recommendations is conflicting and often based on underpowered studies.
QUESTIONS/PURPOSES: (1) What is the association between obesity and DVT and PE after primary and revision THA and TKA? (2) Is there a body mass index (BMI) threshold beyond which DVT and PE risk is elevated?
METHODS: We reviewed the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database from 2008 to 2016 to evaluate the reported 30-day rates of DVT, PE, and combined venous thromboembolism (VTE) after primary THA, primary TKA, revision THA, and revision TKA according to BMI as a continuous variable and a categorical variable as defined by the World Health Organization cutoffs for underweight, normal weight, overweight, and obesity. This database is risk-adjusted and designed to capture complications after surgery, thus making it ideal for this study. The diagnosis of DVT and PE is included in the ACS-NSQIP database for any DVT or PE requiring treatment. Proximal versus distal DVT is not specified within the database. Multivariate logistic regression was performed to determine if obesity was independently associated with DVT and PE risk by controlling for age, sex, race, American Society of Anesthesiologists score, diabetes, hypertension, smoking status, general anesthesia, and hypoalbuminemia.
RESULTS: After controlling for potential confounding variables such as medical comorbidities and procedure type, patients undergoing primary and revision THA and TKA with World Health Organization classification as underweight (BMI < 18.5 kg/m), overweight (BMI 25-29.9 kg/m), Class I obese (BMI 30-34.9 kg/m), Class II obese (BMI 35-39.9 kg/m), or Class III obese (BMI ≥ 40 kg/m) did not demonstrate an association with increased risk of DVT compared with patients classified as normal weight (BMI 18.5-25 kg/m). Compared with patients undergoing primary THA classified as normal weight, the risk of PE was elevated in patients with Class II obesity (odds ratio [OR], 2.36; 95% confidence interval [CI], 1.23-4.50; p = 0.009) and all heavier categories. Compared with patients undergoing TKA classified as normal weight, the risk of PE was elevated in patients classified as overweight (OR, 1.56; 95% CI, 1.03-2.36; p = 0.035) and all heavier categories.
CONCLUSIONS: This large administrative database study suggests that patient classification as overweight or obese is associated with increased risk of development of PE but not DVT after primary THA or TKA. Because aggressive pharmacologic anticoagulation regimens can decrease the DVT rate but have not been shown to affect the rate of PE or death, the data do not currently support increased anticoagulation in patients with obesity without other risk factors for VTE undergoing THA or TKA. Additional studies are required to refine VTE prophylaxis protocols to reduce PE risk while maintaining acceptable postoperative bleeding risk.
LEVEL OF EVIDENCE: Level III, therapeutic study.
