Incidence of Symptomatic Venous Thromboembolism (VTE) in 8,885 Elective Total Hip Arthroplasty Patients Receiving Post-operative Aspirin VTE Prophylaxis

Background: Venous thromboembolism (VTE) is a potentially reducible cause of morbidity and mortality in patients undergoing elective hip arthroplasty surgery. The balance of post-operative VTE prophylaxis and risk of post-operative haemorrhage remains at the forefront of surgeon’s mind. The National Institute for Health and Care Excellence (NICE) published updated guidelines in 2018 which recommend the use of both mechanical and pharmacological methods in patients undergoing elective total hip arthroplasty (THA). Objectives: The aim of this study was to present the symptomatic VTE incidence in 8,885 patients who underwent THA between January 1998 and March 2018 with Aspirin as the primary agent for pharmacological thromboprophylaxis. Intermittent calf compression stockings are routinely used from the time of surgery until mobilization (usually the following day) with prophylactic doses of low molecular weight heparin (LMWH) during inpatient stay (from 2005 onwards) and then Aspirin 150mg once daily for six weeks on hospital discharge (or Aspirin only prior to 2005), with use of other therapies occasionally as required. Methods: Analysis of prospective data collection from consecutive patients at a single institution undergoing THA was performed with the incidence of symptomatic deep vein thrombosis (DVT) and pulmonary embolism (PE) occurring within six months of the index operation as the primary outcome measure. Ninety-day all-cause mortality of this cohort of patients was also analysed. Results: 8,885 patients were reviewed. This included 7230 primary, 224 complex primary and 1431 revision cases. The overall incidence of symptomatic VTE after elective THA was 1.11% (99/8885) - with the incidence of symptomatic DVT of 0.59% (52/8885) and the incidence of symptomatic PE of 0.53% (47/8885). There was no significant difference (χ(2) test, p=0.239) in the symptomatic VTE incidence between primary (1.20% - 89/7230), complex primary (0.89% - 2/224) and revision cases (0.70% - 10/1431). The 90-day all-cause mortality was 0.88% (78/8885). Cardiovascular and respiratory disease were the main causes of death following surgery. Only 0.03% of deaths (n= 3) within 90 days of index surgery were due to PE. There was no significant difference (p=0.327) in length of stay (and hence amount of pharmacologic prophylaxis with LMWH received by patients before commencement of Aspirin) with the average length of stay for those patients who did not suffer a VTE of 6.8 days compared with 7.6 days for those who did suffer a VTE. Conclusion: Our results support the use of aspirin as an effective form of prophylaxis against symptomatic VTE following THA in contradiction to NICE and American Academy of Orthopaedic Surgery (AAOS) recommendations. It is not associated with an increased incidence in symptomatic DVT, PE or death compared to other published studies. The fact that it is inexpensive, readily available, requires no monitoring and does not pose an increased risk of bleeding are other advantages of using aspirin for VTE prophylaxis.