Open Access Highly Accessed Study protocol

Effectiveness of compression stockings to prevent the post-thrombotic syndrome (The SOX Trial and Bio-SOX biomarker substudy): a randomized controlled trial

Susan R Kahn1*, Hadia Shbaklo1, Stan Shapiro12, Philip S Wells3, Michael J Kovacs4, Marc A Rodger56, David R Anderson7, Jeffrey S Ginsberg8, Mira Johri9, Vicky Tagalakis1 and the SOX Trial Investigators

Author Affiliations

1 Centre for Clinical Epidemiology and Community Studies, Jewish General Hospital, Montreal, Quebec, Canada

2 Department of Epidemiology and Biostatistics, McGill University, Montreal, Quebec, Canada

3 Division of Hematology, The Ottawa Hospital, Ottawa, Ontario, Canada

4 Thrombosis Unit, London Health Sciences Centre, London, Ontario, Canada

5 Thrombosis Program, Division of Hematology, University of Ottawa, Ottawa, Ontario, Canada

6 Clinical Epidemiology Program, The Ottawa Hospital-General Campus, Ottawa, Ontario, Canada

7 Thrombosis Unit, Queen Elizabeth II Health Sciences Centre, Halifax, Nova Scotia, Canada

8 Department of Medicine, McMaster University Medical Center, Hamilton, Ontario, Canada

9 Health Administration Department, Université de Montréal, Montreal, Quebec, Canada

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BMC Cardiovascular Disorders 2007, 7:21  doi:10.1186/1471-2261-7-21

Published: 24 July 2007



Post thrombotic syndrome (PTS) is a burdensome and costly complication of deep venous thrombosis (DVT) that develops in 20–40% of patients within 1–2 years after symptomatic DVT. Affected patients have chronic leg pain and swelling and may develop ulcers. Venous valve disruption from the thrombus itself or thrombus-associated mediators of inflammation is considered to be a key initiating event for the development of venous hypertension that often underlies PTS. As existing treatments for PTS are extremely limited, strategies that focus on preventing the development of PTS in patients with DVT are more likely to be effective and cost-effective in reducing its burden. Elastic compression stockings (ECS) could be helpful in preventing PTS; however, data on their effectiveness are scarce and conflicting.


The SOX Trial is a randomized, allocation concealed, double-blind multicenter clinical trial. The objective of the study is to evaluate ECS to prevent PTS. A total of 800 patients with proximal DVT will be randomized to one of 2 treatment groups: ECS or placebo (inactive) stockings worn on the DVT-affected leg daily for 2 years. The primary outcome is the incidence of PTS during follow-up. Secondary outcomes are severity of PTS, venous thromboembolism (VTE) recurrence, death from VTE, quality of life and cost-effectiveness. Outcomes will be evaluated during 6 clinic visits and 2 telephone follow ups. At baseline, 1 and 6 months, blood samples will be obtained to evaluate the role of inflammatory mediators and genetic markers of thrombophilia in the development of PTS (Bio-SOX substudy).


The SOX Trial will be the largest study and the first with a placebo control to evaluate the effectiveness of ECS to prevent PTS. It is designed to provide definitive data on the effects of ECS on the occurrence and severity of PTS, as well as DVT recurrence, cost-effectiveness and quality of life. This study will also prospectively evaluate the predictive role of biomarkers that are reflective of putative underlying pathophysiological mechanisms in the development of clinical PTS. As such, our results will impact directly on the care of patients with DVT.

Trial Registration

NCT00143598 and ISRCTN71334751