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The SOX Trial: Compression Stockings to Prevent the Post-Thrombotic Syndrome

This study has been completed.
Canadian Institutes of Health Research (CIHR)
Sigvaris Corporation
Information provided by (Responsible Party):
Dr. Susan Kahn, Sir Mortimer B. Davis - Jewish General Hospital Identifier:
First received: September 1, 2005
Last updated: August 15, 2014
Last verified: August 2014
Results First Received: June 3, 2014  
Study Type: Interventional
Study Design: Allocation: Randomized;   Endpoint Classification: Efficacy Study;   Intervention Model: Parallel Assignment;   Masking: Double Blind (Subject, Investigator, Outcomes Assessor);   Primary Purpose: Prevention
Condition: Deep Venous Thrombosis
Interventions: Device: Knee-length, graduated elastic compression stocking
Device: Knee-length, placebo stocking

  Participant Flow
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Recruitment Details
Key information relevant to the recruitment process for the overall study, such as dates of the recruitment period and locations
Between June, 2004, and February, 2010, we enrolled patients in 24 centres in Canada and the USA.

Pre-Assignment Details
Significant events and approaches for the overall study following participant enrollment, but prior to group assignment
Patients were excluded if they had a contraindication to the use of compression stockings, an expected life span of <6 months, geographical inaccessibility, were unable to apply stockings, or received thrombolytic therapy for the initial treatment of acute deep vein thrombosis (DVT).

Reporting Groups
Active ECS Active Elastic Compression Stockings. 30-40 mm Hg
Placebo ECS Placebo stockings with identical appearance but less than 5 mm Hg compression at the ankle.

Participant Flow:   Overall Study
    Active ECS     Placebo ECS  
STARTED     410     396  
COMPLETED     318     302  
NOT COMPLETED     92     94  
Lost to Follow-up                 23                 21  
Withdrawal by Subject                 33                 37  
Death                 36                 36  

  Baseline Characteristics
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Population Description
Explanation of how the number of participants for analysis was determined. Includes whether analysis was per protocol, intention to treat, or another method. Also provides relevant details such as imputation technique, as appropriate.
806 patients were randomly assigned to an intervention. Three patients were identified as ineligible soon after randomization and were excluded from further analysis (ie, modified intention-to-treat). In the active ECS group, one patient had no DVT and in the placebo ECS group one patient had a previous DVT and another patient was moribund.

Reporting Groups
Active ECS Active Elastic Compression Stockings. 30-40 mm Hg
Placebo ECS Placebo stockings with identical appearance but less than 5 mm Hg compression at the ankle.
Total Total of all reporting groups

Baseline Measures
    Active ECS     Placebo ECS     Total  
Number of Participants  
[units: participants]
  409     394     803  
[units: years]
Mean (Standard Deviation)
  55.4  (15.3)     54.8  (15.8)     55.1  (15.5)  
Age, Customized  
[units: participants]
<40 years     67     67     134  
40-65 years     222     217     439  
>65 years     120     110     230  
[units: participants]
Female     154     166     320  
Male     255     228     483  
Race/Ethnicity, Customized  
[units: participants]
White ethnic origin     371     354     725  
[units: participants]
  355     344     699  
Body-mass index, kg/m2  
[units: kg/m^2]
Mean (Standard Deviation)
  29.0  (6.1)     28.9  (6.1)     28.95  (6.1)  
Time from DVT diagnosis to randomization  
[units: days]
Mean (Standard Deviation)
  4.8  (4.1)     4.6  (3.8)     4.7  (3.9)  
Side of DVT  
[units: participants]
Left     180     173     353  
Right     222     216     438  
Bilateral     7     5     12  
Most proximal extent of DVT  
[units: participants]
Iliac vein     44     49     93  
Common femoral vein     109     107     216  
Femoral Vein     128     123     251  
Popliteal vein     128     115     243  
Villalta score at baseline [1]
[units: Score on a scale]
Mean (Standard Deviation)
  8.2  (4.4)     8.7  (4.8)     8.4  (4.6)  
Concurrent pulmonary embolism  
[units: participants]
  57     57     114  
Venous thrombosis risk factors  
[units: participants]
Surgery, past 3 months     77     64     141  
Trauma, past 3 months     42     51     93  
Immobilised in past month     67     61     128  
Active cancer     52     46     98  
Pregnant, post partum, OCT, or HRT     37     55     92  
Family history of venous thromboembolism     85     82     167  
Type of DVT Treatment  
[units: participants]
Low molecular weight heparin     388     384     772  
Unfractionated heparin     31     21     52  
Warfarin     330     317     647  
Investigational anitcoagulant     15     11     26  
Duration of DVT Treatment  
[units: days]
Median (Inter-Quartile Range)
Duration of heparin     8  
  (6 to 11)  
  (6 to 10)  
  (6 to 11)  
Duration of Oral Anti-Coagulation (OAC)     186  
  (113 to 253)  
  (104 to 220)  
  (109.5 to 231)  

The Villalta Scale for assessment of the post-thrombotic syndrome

The Villalta scale has a range of 0-33. A Villalta scale score >4 indicates post-thrombotic syndrome (severity of post-thrombotic syndrome is categorized as 5-9 points, mild; 10-14 points, moderate; >14 points or presence of an ulcer, severe).

Higher values signify worse outcome.

Points on each item in the scale are simply summed to a total score.

  Outcome Measures
  Show All Outcome Measures

1.  Primary:   Incidence of Post-thrombotic Syndrome (PTS)   [ Time Frame: During 2-year follow up ]

2.  Secondary:   Severity of PTS, Including Incidence of Venous Ulcer   [ Time Frame: 6-24 months. ]

3.  Secondary:   Incidence of Objectively Confirmed Recurrent Venous Thromboembolism (VTE), Death From VTE and Major Bleeding   [ Time Frame: During 2-year follow up ]

4.  Secondary:   Quality of Life   [ Time Frame: 24 months ]

  Serious Adverse Events

  Other Adverse Events

  Limitations and Caveats
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Limitations of the study, such as early termination leading to small numbers of participants analyzed and technical problems with measurement leading to unreliable or uninterpretable data
While 14% withdrew or were lost to follow-up (F/U), the total rate of withdrawal, loss to F/U and death was less than what was projected. Adherence to study stockings tended to diminish over F/U; this occurred to a similar degree in both groups.

  More Information
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Certain Agreements:  
Principal Investigators are NOT employed by the organization sponsoring the study.
There is NOT an agreement between Principal Investigators and the Sponsor (or its agents) that restricts the PI's rights to discuss or publish trial results after the trial is completed.

Results Point of Contact:  
Name/Title: Dr. Susan R Kahn
Organization: Centre for Clinical Epidemiology, Jewish General Hospital
phone: 514-340-8222 ext 7587

Publications of Results:
Other Publications:
Publications automatically indexed to this study by Identifier (NCT Number):

Responsible Party: Dr. Susan Kahn, Sir Mortimer B. Davis - Jewish General Hospital Identifier: NCT00143598     History of Changes
Other Study ID Numbers: MCT-63142
ISRCTN71334751 ( Registry Identifier: ISRCTN )
Study First Received: September 1, 2005
Results First Received: June 3, 2014
Last Updated: August 15, 2014
Health Authority: Canada: Health Canada