A new, randomized controlled study of 9,711 patients pits aspirin against enoxaparin as a treatment for symptomatic venous thromboembolism (VTE) after total joint arthroplasty. The study was put together by the CRISTAL study group and designed to be a cluster-randomized, crossover, non-inferiority trial of aspirin compared to low molecular weight heparin for venous thromboembolism prophylaxis in hip or knee arthroplasty. It was a registry nested study. (In a crossover trial, participants are randomly allocated to study arms where each arm consists of a sequence of two or more treatments given consecutively.)1
The research, “Effect of Aspirin vs Enoxaparin on Symptomatic Venous Thromboembolism in Patients Undergoing Hip or Knee Arthroplasty: The CRISTAL Randomized Trial,” appears in the August 23, 2022, edition of The Journal of the American Medical Association.
Co-author Verinder Sidhu, M.B.B.S., with the Whitlam Orthopaedic Research Centre, Ingham Institute for Applied Medical Research, University of New South Wales in Australia, told OTW, “The use of aspirin monotherapy for VTE (deep venous thrombosis or pulmonary embolus) prophylaxis after total hip [THA] and total knee arthroplasty [THA] has increased throughout the United States and Australia over the last decade, despite a lack of evidence for its safety and efficacy from randomized controlled trials comparing it to more established treatments (such as rivaroxaban, enoxaparin and warfarin).”
“Given the large increase in aspirin use, largely driven by retrospective cohort studies (which have a large amount of inherent bias in their methodology), a randomized controlled trial was needed to further investigate this subject.”
The team collected data from 31 hospitals in Australia, with clusters being hospitals that did more than 250 THA or TKA procedures a year. A total of 9,711 eligible patients were enrolled (5,675 in the aspirin group and 4,036 in the enoxaparin group) between April 20, 2019, and December 18, 2020; 9,203 (95%) completed the trial.
Enoxaparin Stands Out
“The most important result,” explained Dr. Sidhu to OTW, “was the primary outcome: the symptomatic VTE rate within 90 days in the aspirin group was 3.45% and was 1.82% in the enoxaparin group, which was significant for the superiority of enoxaparin (p<0.007). The superiority of enoxaparin did not lead to an increase rate of secondary complications, such as major bleeding, mortality, joint related reoperation or joint related readmission within 90 days.”
“The results of this trial demonstrate that enoxaparin was superior to aspirin in preventing symptomatic 90-day VTE after total hip and total knee arthroplasty performed for a diagnosis of osteoarthritis. We are awaiting to determine the effect on practice change and plan to do a follow-up survey to determine if prescribing practice has changed following this trial.”
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