CAN ASPIRIN REDUCE VTE RISK IN HIP FRACTURE SURGERY PATIENTS? A COMPARISON OF PLATELET ACTIVITY IN URGENT HIP FRACTURE SURGERY AND ELECTIVE TOTAL HIP ARTHROPLASTY

Platelets play a critical role in clot formation through several pathways. Acetylsalicylic acid (ASA; aspirin) is an antiplatelet medication that inhibits the arachidonic acid (AA) pathway, and has shown effectiveness in preventing venous thromboembolism (VTE) following total hip arthroplasty (THA). As a result, many orthopaedic surgeons now routinely use ASA for VTE prophylaxis after THA. However, this practice has not been widely adopted in the hip fracture surgery (HFS) population, where high-quality evidence on the use of ASA remains limited. Thrombelastography (TEG) is a point-of-care tool that provides a comprehensive assessment of individual coagulation profiles. The maximal amplitude (MA) parameter, which reflects clot strength, has been used to define hypercoagulability and identify patients at risk for VTE. Previous studies, including our own, have shown that while coagulation profiles are similar in THA and HFS patients, those undergoing HFS tend to be more hypercoagulable in the early postoperative period and experience a higher incidence of VTE. TEG-based Platelet Mapping (PLM) allows for the evaluation of platelet activity and its contribution to clot strength, providing insights into the potential efficacy of antiplatelet therapy. This study aimed to compare platelet hyperactivity and platelet inhibition in patients undergoing THA and HFS. This is a prospective cohort study enrolled patient aged 50 or older who underwent primary THA or urgent HFS, excluding those with a history of VTE, anticoagulant use, bleeding disorders, or active malignancies. Serial whole blood samples were collected preoperatively and up to 12-weeks postoperatively, and analysed using a TEG6s hemostasis analyser (Haemonetics Corporation, Braintree, MA) with PLM. Thromboprophylaxis included ASA 81 mg daily for 28 days following THA, while most HFS patients received tinzaparin 4500 units daily for 35 days, with nine patients prescribed ASA at varying doses. Mann-Whitney U tests were used to compare mean AA-MA and platelet inhibition values at each timepoint. The study included 37 patients undergoing THA and 169 undergoing HFS, with mean ages of 68.4 ± 9.0 years and 77.5 ± 11.0 years, respectively (p The HFS group exhibited significantly higher platelet hyperactivity at all timepoints, except at 12-weeks postoperatively (p = 0.60). Postoperatively, platelet inhibition was significantly lower in the HFS group up to 6-weeks. Among HFS patients prescribed ASA, there were no significant differences in platelet activity relative to the THA group, except at 4-weeks. A total of 11 HFS patients experienced VTE events, primarily during the early postoperative period when platelet hyperactivity was most pronounced. Two THA patients also suffered from VTE events, both of whom showed significant platelet hyperactivity (p = 0.02) and decreased platelet inhibition (p = 0.04) on postoperative day 1 compared to those without VTE events. However, in the HFS group, there were no significant differences in platelet hyperactivity or inhibition between those who did and did not experience VTE events at any timepoint. This study found higher platelet hyperactivity and reduced platelet inhibition in patients undergoing HFS compared to those undergoing THA, suggesting that the increased incidence of VTE in the HFS group may be related to greater platelet contribution to clot formation. These findings support the potential benefit of using ASA as an antiplatelet prophylactic for HFS patients to reduce VTE risk. Although VTE events also occurred in the THA group, these two patients exhibited elevated platelet hyperactivity and decreased platelet inhibition despite ASA use, which may indicate ASA resistance. This highlights the importance of a personalized approach to postoperative VTE prevention.