Association of obesity with thromboembolic complications after hip fracture surgery: a tertiary center retrospective cohort study (HipCLOTS)

Background: Patients undergoing hip fracture surgery are at an increased risk of thromboembolic complications, but the impact of obesity on the outcomes remains poorly understood. We aimed to investigate arterial and venous thromboembolic complications following hip fracture surgery and their association with body mass index (BMI). Materials and methods: In this retrospective cohort study at a tertiary referral center, patients aged ≥ 60 years who underwent hip fracture surgery between 2010 and 2020, were categorized by BMI (underweight, normal weight, overweight and obese). The primary outcome was the occurrence of thromboembolic complications within 90 days post-surgery. The secondary outcomes included systemic complications and all-cause mortality within a year. Regression analysis was performed to assess BMI’s association with outcomes, considering the competing risk of death. Results: Out of the 1853 patients, 214 (11.5%) experienced 90-day thromboembolic complications. Myocardial infarction was most prevalent in the underweight (7.4 %; n = 20) followed by obese patients (6.4 %; n = 13). Deep venous thrombosis and pulmonary embolism mostly occurred in the overweight (7.4%; n = 33) and ischemic stroke in the obese patients (2.5%; n = 5). Adjusted competing risk analysis for 90-day thromboembolic complications revealed that overweight and obese patients were at higher risk compared to normal BMI group, with adjusted sub-hazard ratios of 1.80 (95 % CI: 1.04 − 3.10; P = 0.04), and 2.39 (95% CI: 1.28- 4.49; P = 0.006) respectively. Compared to individuals with a normal BMI, underweight category had increased odds (OR: 1.6; 95% CI: 1.2-2.3; P = 0.002) while obese category had decreased odds (OR: 0.5; 95 % CI 0.3-0.8; P = 0.005) of one-year mortality. Conclusions: BMI is significantly associated with 90-day thromboembolic complications and one-year mortality following hip fracture surgery. This highlights the need for prolonged thromboprophylaxis and regular follow-up in this patient group.