Patients developing arthritis of the hip and knee joints no longer want to put up with the pain and disability that follows. Most of them want their joints replaced quickly so that they can resume their normal activities without pain. The joints that are available today are so good that theylast a long time. However joint replacement surgery is a major procedure and does carry a certain amount of risk. One of them is the risk of developing venous thromboembolism.

The embolus usually commences as a DVT in the leg when the leg remains still during surgery and the immediate post-operative period.
The Virchow triad, consisting of a combination of endothelial damage, venous stasis and hypercoagulability, can trigger the development of thrombosis. All three components are relevant in lower limb arthroplasty.

The development of a venous thrombus often starts in the region of a valve where the pattern of blood flow becomes abnormal, resulting in endothelial dysfunction. Stagnant blood in a linear section of the blood vessel leads to hypoxia, which in turn initiates thrombogenesis and the aggregation of platelets.

To prevent VTE most patients are prescribed anticoagulants. The selection of a particular anticoagulant relies on the balance between the desire to minimise VTE and the attempt to reduce the risk of bleeding, with its undesirable, and occasionally fatal, consequence.
Two commonly used agents to prevent a thromboembolism are Aspirin (acetylsalicylic acid) and low molecular weight heparin. Most surgeons in Europe tend to use LMWH. The trend in USA has been to use aspirin. The surgeons who are reluctant to use aspirin worry about its side effects ie the risk of bleeding and subsequent haematoma formation.

An excellent article was published recently in Bone Joint Journal by Azboy, Barrack, Thomas, Haddad, and Parvizi (2017;99-B:1420–30) trying to summarise the current evidence relating to the efficacy of aspirin as a VTE prophylaxis following arthroplasty, and address some of the common questions about its use.

They state that there is convincing evidence that aspirin is effective and safe to use in joint replacement surgery. It is also cheap and its use does not require routine blood monitoring as will be required when LMWH is used. In recent years, there has been a dramatic shift, at least in North America, towards the use of aspirin as the main modality for VTE prophylaxis following arthroplasty. A recent poll of >1200 attendees of the annual meeting of the American Association of Hip and Knee Surgeons, in 2016, revealed that >80% use aspirin as the main prophylaxis for their patients undergoing arthroplasty of the hip or knee.

There are other reasons why aspirin is being used in North America. One may relate to the advances in anaesthesia and surgical techniques that have changed the nature of arthroplasty. The use of regional anaesthesia, multimodal pain management with less reliance on opioids, and the effective conservation of blood allows most patients to walk within hours of their surgery. Many centres around the world now undertake arthroplasty as an outpatient procedure.

One of the most important and commonly cited studies is the Pulmonary Embolism Prevention (PEP) Trial – (Lancet 2000;355:1295–1302).This multinational and prospective study, involving more than 24 000 patients, confirmed the efficacy of aspirin in the prevention of VTE for patients undergoing arthroplasty and for those with a fracture of the hip. The use of aspirin reduced the incidence of PE and DVT post-operatively by at least a third. The study concluded that “there is now good evidence for considering aspirin routinely in a wide range of surgical and medical groups at high risk of VTE”. The publication of many further studies showing the same thing resulted in the American College of Chest Physicians (ACCP) endorsing aspirin with the highest grade of recommendation, and for the American Academy of Orthopaedic Surgeons (AAOS) to accept aspirin as prophylaxis for patients undergoing arthroplasty.