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Lower limb immobilisation and venous thromboembolism risk: combined case–control studies
  1. Irene Braithwaite1,2,
  2. Bridget Healy1,2,
  3. Laird Cameron1,2,
  4. Mark Weatherall3,
  5. Richard Beasley1,2
  1. 1Medical Research Institute of New Zealand, Wellington, New Zealand
  2. 2Department of Medicine, Capital and Coast District Health Board, Wellington, New Zealand
  3. 3Rehabilitation Teaching and Research Unit, University of Otago Wellington, Wellington, New Zealand
  1. Correspondence to Dr Irene Braithwaite, Medical Research Institute of New Zealand, Private Bag 7902, Wellington 6242, New Zealand; Irene.braithwaite{at}


Background Evidence from randomised controlled trials shows that low-molecular-weight heparin is effective in reducing the risk of venous thromboembolism (VTE) in the clinical setting of temporary lower limb immobilisation. Despite this, international guidelines are non-committal in advocating the use of anticoagulation in this clinical scenario. We determined the risk of VTE associated with lower limb immobilisation and the proportion of VTE events associated with lower limb immobilisation by undertaking a secondary analysis of two case–control studies that had used a similar methodology.

Methods We undertook logistic regression analysis to investigate the association of risk factors with VTE with the OR and 95% CIs for association between lower limb immobilisation and VTE the primary outcome variable. The proportion of VTE patients with lower limb immobilisation was also calculated.

Results Cases comprised 396 patients aged 18–65 years with radiologically confirmed deep vein thrombosis or pulmonary embolism attending outpatient VTE clinics. Controls, also aged 18–65 years, comprised 197 inpatients in the coronary care unit and 200 outpatients treated for upper limb injuries in the fracture clinic. The OR for association between VTE and lower limb immobilisation was 73.1 (95% CI 10.1 to 530, p<0.001). In 62/396 (16%) cases, patients had undergone lower limb immobilisation within four weeks of their presentation with VTE, representing the most common potentially preventable cause of VTE in this sample.

Conclusions Lower limb immobilisation is associated with a markedly increased risk of VTE and represents the most common potentially preventable cause in the 18–65-year age group, being present in one in seven cases treated for VTE. Consideration should be given to pharmacological prophylaxis in patients with lower limb immobilisation to reduce the substantial burden of preventable VTE.

  • cast
  • surgical
  • immobilisation
  • lower extremity
  • venous thromboembolism
  • deep vein thrombosis

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  • Contributors Study design: IB, MW and RB. Data collection: IB, CL and BH. Analysis: MW and IB. Interpretation: all authors. Manuscript drafting: IB. Critical review of manuscript: all authors. Supervision: RB and MW. IB had access to all the data on the study and takes responsibility for the integrity of the data and accuracy of the data analysis.

  • Funding IB was funded through the Health Research Council of New Zealand (HRC) by way of a Clinical Training Fellowship to undertake a PhD (14/040), and the Medical Research Institute of New Zealand also receives funding from the HRC through the Independent Research Organisations Capability Fund (14/1002). 

  • Disclaimer The funding parties had no involvement in the design or preparation of the study, collection, analysis and interpretation of the data, or the decision to submit for publication.

  • Competing interests None declared.

  • Patient consent Obtained.

  • Ethics approval Both case–control studies were individually approved by the New Zealand Health and Disability Ethics Committees (CEN/05/08/054 and CEN/09/04/013, respectively).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement Patient-level data available from the corresponding author on request. Consent was not obtained from participants for data sharing, but the presented data are anonymised and the risk of identification is low.