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

The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been evaluated by the U.S. Federal Government. Read our disclaimer for details. Identifier: NCT00143598
Recruitment Status : Completed
First Posted : September 2, 2005
Results First Posted : August 18, 2014
Last Update Posted : August 18, 2014
Canadian Institutes of Health Research (CIHR)
Sigvaris Corporation
Information provided by (Responsible Party):
Dr. Susan Kahn, Sir Mortimer B. Davis - Jewish General Hospital

Study Type: Interventional
Study Design: Allocation: Randomized;   Intervention Model: Parallel Assignment;   Masking: Triple (Participant, 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

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

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 
Overall Participants Analyzed 
[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) 

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.

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) 

  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

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

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 )
First Submitted: September 1, 2005
First Posted: September 2, 2005
Results First Submitted: June 3, 2014
Results First Posted: August 18, 2014
Last Update Posted: August 18, 2014