Lower limb immobilisation and venous thromboembolism risk: combined case-control studies

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.