This paper is an important addition to the literature. It challenges previous assumptions and will make the reader reconsider his/her practice.
Some criticise thromboprophylaxis in orthopaedics because they believe that venous thrombosis is an imaginary radiological phenomenon. This paper, only observing symptomatic events, found that 6.3% had a deep-vein thrombosis (DVT) or pulmonary embolisom (PE). This is a high proportion - greater than that seen after hip replacement. This is not imaginary. Furthermore, symptomatic events only represent the tip of an iceberg; for every symptomatic DVT or PE there will probably be three asymptomatic events. It is usually asymptomtic DVTs which embolise and kill.
The recent NICE guidelines1 , concerning lower limb plaster casts, recommend: “(1.6.3) Consider offering pharmacological VTE prophylaxis to patients with lower limb plaster casts after evaluating the risks (see section 1.1) and benefits based on clinical discussion with the patient. Offer LMWH (or UFH for patients with renal failure) until lower limb plaster cast removal.”
This advice, to which UK orthopaedic surgeons are expected to adhere, suggests a risk assessment. Some risk factors are obvious such as a previous history of VTE, varicose veins, obesity and malignancy. Some are occult including rare coagulopathies such as Leiden factor deficiency (as found in one of the patients in this study after the VTE had been diagnosed). However, VTE usually occurs sporadically without any obvious risk factor apart from the orthopaedic intervention and consequent immobility.
The high rate of symptomatic VTE in this study suggests that it is the rupture of the tendo Achillis and its treatment with prolonged plaster immobilisation and sometimes surgery, which conveys the high risk. If so, routine risk assessment for these patients would lead to mandatory and universal thromboprophylaxis.
The accumulation of evidence shows that LMWH does reduce the rate of VTE after plaster immobilisation2,3 although its administration for several weeks poses pragmatic issues and risks thrombocytopenia in a very small proportion risks. An oral agent would be preferable. Aspirin is unlikely to be effective and Warfarin, whether effective or not, is complicated and risks significant complications. We now have oral agents (Dabigitran and Rivaroxaban) available, effective and approved for use in hip and knee arthroplasty. Should we not support a randomized trial in the setting of plaster cast immobilization? If so, given the demonstrable risk and the known benefit of LMWH, the trial would have to compare one of these drugs with LMWH as it would be unethical to use a placebo. As a simpler and more expeditious solution, one could extrapolate the results from joint arthroplasty and use these drugs “off label” if appropriate funding was available.
The authors of this study should be praised for highlighting the real clinical risk and for providing such a comprehensive and well-written discussion of the issues.
2. Ettema HB, Kollen BJ, Verheyen CC, Buller HR. Prevention of venous thromboembolism in patients with immobilization of the lower limb extremities: a meta-analysis of randomized controlled trials. J Thromb Haemostas 2008;6:1093-8.
3. Testroote M, Stigter WAH, de Visser DC, Janzing HMJ. Low Molecular weight heparin for prevention of venous thromboembolism in patients with lower-leg immobilization. Cochrane Database of Systematic Reviews 2008;4:CD006681.
Warwick D, MD, RFCS, FRCS(Orth), Reader in Orthopaedics
Southampton University Hospitals, Southampton, United Kingdom