Excess risk of venous thromboembolism in hip fracture patients and the prognostic impact of comorbidity

Hip fracture patients were at increased excess risk of venous thromboembolism (VTE) up to 1 year following hip fracture. During the first year, interaction between hip fracture and comorbidity was observed among patients with severe and very severe comorbidity. We compared the risk of VTE in hip fracture patients with that in the general population. We also examined whether and to what extent the association between hip fracture and VTE varied by comorbidity level. Nationwide cohort study based on Danish health registries, 1995-2015. We identified hip fracture patients (n = 110,563) and sampled a comparison cohort without hip fracture from the general population (n = 552,774). Comorbidity was assessed using the Charlson comorbidity index. We calculated attributable fraction, as the proportion of the VTE rate, among persons exposed to both hip fracture and comorbidity, attributed to exposure interaction. The cumulative incidences of VTE were 0.73% within 30 days and 0.83% within 31-365 days among hip fracture patients, and 0.05 and 0.43% in the general population. Adjusted hazard ratios (HRs) of VTE among hip fracture patients were 17.29 [95% confidence interval (CI) 14.74-20.28] during the first 30 days and 2.13 (95% CI 1.95-2.32) during 31-365 days following hip fracture. The relative risks of VTE were 1.03 (95% CI 0.96-1.11) and 1.11 (95% CI 1.00-1.23) after 1-5 years and 6-10 years. During the first 30 days and 31-365 days, 14%/28% of VTE rates and 5%/4% of VTE rates were attributable to the interaction between hip fracture and severe/very severe comorbidity, respectively. Mortality risks within 30 days of VTE were 29.4% in hip fracture and 11.0% in general population cohorts. Hip fracture patients were at increased excess risk of VTE up to 1 year following their fracture. During the first year, interaction between hip fracture and comorbidity was observed among patients with severe and very severe comorbidity.