Aspirin for the Prophylaxis of Venous Thromboembolic Events in Orthopedic Surgery Patients

A Comparison of the AAOS and ACCP Guidelines With Review of the Evidence

David W Stewart PharmD BCPS; Jessica E Freshour PharmD


The Annals of Pharmacotherapy. 2013;47(1):63-74. 

In This Article

Abstract and Introduction


Background: The American Academy of Orthopaedic Surgeons (AAOS) and the American College of Chest Physicians (ACCP) have both developed evidence-based guidelines to prevent venous thromboembolism (VTE) in high-risk orthopedic surgery patients. Recent changes to these documents have brought them into agreement as to the inclusion of aspirin as an appropriate option for VTE prophylaxis in this patient population.

Objective: To evaluate the appropriateness of aspirin to prevent VTE in high-risk orthopedic surgery patients.

Data sources: Guidelines published by the AAOS in 2011 and the ACCP in 2012 were compared regarding their recommendations on the use of aspirin for the prevention of VTE. A literature search was also conducted to identify clinical trials that evaluated the use of aspirin for the prevention of VTE in this patient population. Search terms included the MeSH terms venous thromboembolism; venous thrombosis; pulmonary embolism; aspirin; arthroplasty, replacement, knee; arthroplasty, replacement, hip; and hip fractures/surgery.

Study selection and data extraction: Any study that evaluated aspirin, even in combination with another method of prophylaxis (such as pneumatic compression devices), and had been published during or after 1985 was included.

Data synthesis: Randomized controlled trials, meta-analyses, and other large pooled and retrospective reviews have failed to consistently arrive at similar conclusions regarding the efficacy and safety of aspirin as an option for VTE prophylaxis in patients undergoing total knee arthroplasty (TKA), total hip arthroplasty (THA), or hip fracture surgery (HFS). Disagreements in the appropriateness of surrogate markers for safety and efficacy have resulted in differing recommendations from the ACCP and AAOS. The primary argument lies in the appropriateness of deep vein thrombosis as a surrogate marker for more serious outcomes such as pulmonary emboli.

Conclusions: Recent changes to both the ACCP and AAOS guidelines are in agreement for those who choose to use aspirin for chemoprophylaxis of VTE. Current surgical care improvement project measures do not include aspirin as an appropriate sole option for the prevention of VTE, but in patients undergoing elective TKA or who have a contraindication to pharmacologic prophylaxis and undergo a THA or HFS, aspirin in conjunction with compression devices as part of a multimodal approach would meet these measures. Data do not support the hypothesis that aspirin is less likely to cause adverse bleeding events than more potent anticoagulants.


Patients undergoing high-risk orthopedic procedures, and specifically, total hip arthroplasty (THA), total knee arthroplasty (TKA), and hip fracture repair surgery (HFS), are at a significantly increased risk of venous thromboembolic events (VTE), with rates historically estimated at as high as 60% without appropriate prophylaxis.[1] However, this overarching estimate is not well defined as to type and location of events. A more recent attempt to quantify rates of symptomatic VTE in this patient population estimates that prior to 1980, without prophylaxis, the event rate was approximately 15–30%, with a reduction to 1–2% by 2001 with contemporary prophylactic strategies.[2] The appropriate preventative strategy for VTE in high-risk orthopedic surgery patients (defined here as THA, TKA, and HFS) has been debated over the last 30–40 years, with the argument revolving around appropriateness of surrogate markers and/or outcomes, as well as the likelihood of adverse events; specifically, whether or not nonfatal and nonsymptomatic events are important outcomes to consider in clinical trials.[1,3–5]

Guidelines have been developed by both the American College of Chest Physicians (ACCP) and the American Academy of Orthopaedic Surgeons (AAOS) to address the issue of prophylaxis in this high-risk population.[2,6] Both documents were recently updated with significant changes. Most notably, the ACCP document now devotes a specific chapter to the prevention of VTE in orthopedic surgery patients,[2] and the AAOS changed the document title to reflect prevention of all VTE, in contrast to pulmonary embolism (PE) only.[6] Both guideline statements are evidence based; however, there are differences in their methodology (Table 1). Of note, the AAOS document still does not recognize deep vein thrombosis (DVT; symptomatic or asymptomatic) as an acceptable surrogate marker for potential complications associated with VTE, despite the change in the document's title. The AAOS puts a greater emphasis on the risk of bleeding from surgical wounds than does the ACCP, which is reflected in the recommendations set forth by each organization.

In previous versions of these documents, the use of aspirin as an option for the prevention of fatal PE has differed. ACCP specifically recommended against aspirin in all instances,[1] while the AAOS recommends aspirin for some patients at higher risk of adverse bleeding events.[7] There was a major difference in accepted outcomes and surrogate markers (all DVT and PE vs symptomatic PE only) for clinical decision making, with the lack of use of asymptomatic or symptomatic DVT as an outcome being a major criticism of the AAOS document.[8] A review incorporating data from the large PEP trial[9] (Pulmonary Embolism Prevention) asserts that the question of whether or not aspirin is as effective as low-molecular-weight heparin (LMWH) in contemporary practice has yet to be answered.[10,11]

A common problem that plagued most studies on this topic through the mid-1980s was the failure to adequately power clinical trials or use appropriate statistical tests to assess outcomes. Multiple studies[12–15] compared aspirin to other anticoagulants in a head-to-head fashion and reported that aspirin was as effective as the comparator. However, statistical power was not achieved or reported. Additional studies showing the benefit of aspirin also suffered from issues of power or failed to provide appropriate descriptions of the statistical analyses used.[16–20] These trials failed to meet current standards of comparative effectiveness research,[21] and both the AAOS and ACCP have developed robust statistical and analytical methods to overcome this problem through systematic reviews of the collective literature.