Prevalence of risk factors for venous thromboembolism and aspirin resistance in Australian patients undergoing total hip and knee arthroplasty

Introduction: Aspirin is used for venous thromboembolism (VTE) prophylaxis after total hip and knee arthroplasty (THA/TKA). However, its efficacy is unclear in patients with multiple VTE risk factors and at risk of aspirin resistance (AR). Background and Aims: To determine the prevalence of risk factors for VTE and AR in patients after THA/TKA and to determine the relationship between risk factors and drugs prescribed for thromboprophylaxis. Methods: A retrospective cohort study of elective-THA/TKA in six Australian hospitals over a 1-year period. Medical records were manually reviewed to determine demographics, thromboprophylaxis regimen and presence of risk factors. The relationship between individual and cumulative risk factors with the thromboprophylaxis regimen was determined. Results: In total, 1011 patients were included with a mean (SD) age of 65.9 (+/- 11.0) years, and 56.4% were female. The five most prevalent risk factors were obesity (59.1%), age >= 65 years (58.2%), hypertension (45.3%), dyslipidaemia (35.9%) and diabetes (19.7%). Most patients had >= 1 risk factor for VTE (93.6%) and AR (93.6%), with 49.0% and 35.0% having >= 3 concurrent VTE and AR risk factors, respectively. The only significant relationship between risk factors and drugs was diabetes (P < 0.01). Rivaroxaban was more commonly used as the number of concurrent VTE risk factors increased (P < 0.05). Conclusion: Patients had a high prevalence of VTE and AR risk factors, suggesting aspirin may not be beneficial in many patients. Only diabetes was linked to the selection of thromboprophylaxis. Patients who received rivaroxaban had a greater average number of VTE risk factors. Guidelines should promote individualised prescribing in higher-risk patients.