Risk Factors for Venous Thromboembolism in Patients Undergoing Total Hip Replacement and Receiving Routine Thromboprophylaxis

Background: Data on the risk factors for venous thromboembolism among patients undergoing total hip replacement and receiving pharmacological thromboprophylaxis are limited. The purpose of this study was to examine potential patient-related risk factors for venous thromboembolism following total hip replacement in a nationwide follow-up study. Methods: Using medical databases, we identified all patients who underwent primary total hip replacement and received pharmacological thromboprophylaxis in Denmark from 1995 to 2006. The outcome measure was hospitalization with venous thromboembolism within ninety days of surgery. We considered age, sex, indication for primary total hip replacement, calendar year of surgery, and comorbidity history as potential risk factors. Results: The overall rate of hospitalization for venous thromboembolism within ninety days following a primary total hip replacement was 1.02% (686 hospitalizations after 67,469 procedures) at a median of twenty-two days. The incidence of symptomatic deep venous thrombosis and of nonfatal pulmonary embolism was 0.7% (499 of 67,469) and 0.3% (205 of 67,469), respectively. The incidence of death due to venous thromboembolism or from all causes was 0.05% (thirty-eight patients) and 1.0% (678 patients), respectively. Patients with rheumatoid arthritis had a reduced relative risk for venous thromboembolism compared with patients with primary osteoarthritis (adjusted relative risk = 0.47; 95% confidence interval, 0.25 to 0.90). Patients with a high score on the Charlson comorbidity index had an increased relative risk for venous thromboembolism compared with patients with a low score (adjusted relative risk = 1.45; 95% confidence interval, 1.02 to 2.05). Patients with a history of cardiovascular disease (relative risk = 1.40; 95% confidence interval, 1.15 to 1.70) or prior venous thromboembolism (relative risk = 8.09; 95% confidence interval, 6.07 to 10.77) had an increased risk for venous thromboembolism compared with patients without that history. Conclusions: The cumulative incidence of a venous thromboembolism within ninety days of surgery among patients with total hip replacement receiving pharmacological thromboprophylaxis was 1%. This information on the associated risk factors could be used to better anticipate the risk of venous thromboembolism for an individual patient.