Incidence and risk factors associated with venous thromboembolism following primary total hip arthroplasty in low-risk patients when using aspirin for prophylaxis

Aims: The primary aim was to assess the incidence of venous thromboembolism (VTE) following total hip replacements (THR) in a low-risk patient group when using 150 mg aspirin as the pharmacological component of VTE prophylaxis on discharge. The secondary aim was to identify factors associated with an increased risk of a VTE event in this low-risk group. Patients and methods: Retrospective review of a consecutive cohort of patients undergoing THR during a 63-month period. Patient demographics, socio-economic status, ASA grade, type of anaesthetic, length of surgery and BMI were recorded. A diagnosis of VTE was assigned to symptomatic patients with positive imaging for a deep vein thrombosis (DVT) and/or a pulmonary embolism (PE) within 8 weeks of surgery. Multivariate logistic regression modeling was used to identify factors associated with VTE after THR. Results: 3880 patients underwent THR during the study period, of which 2740 (71%) were low risk and prescribed aspirin for VTE prophylaxis. There were 34 VTE events, of which 15 were DVTs and 18 were PEs, with 1 patient diagnosed with both. The incidence of VTE was 1.2%, with no VTE-related deaths. Patients incurring a VTE postoperatively were more likely to be male (odds ratio [OR] 2.06, p = 0.022), of older age (OR 0.43, p = 0.047) and were more likely to be socially deprived (OR 0.32, p = 0.006). There was no significant difference with patients given low-molecular-weight heparin (LMWH) as an inpatient prior to discharge on aspirin (p = 0.806), nor any difference with the type of anaesthetic used during surgery (p = 0.719) Conclusions: Aspirin is a relatively safe and effective choice for VTE prophylaxis in low-risk patients undergoing THR. Male sex and age >70 years were twice as likely to sustain a VTE and patients from the most deprived socio-economic background are 3 times as likely.