Venous blood flow, thromboembolism and below knee cast immobilisation for trauma

Venous thromboembolism (VTE) has a background incidence of between 0.7 and 2.69 per 1000 per year (L. N. Roberts et al., 2013). Risk factors are either permanent or transient. Permanent risk factors include thrombophilia (80 x increase risk if homozygous for factor V Leiden), cancer (58 x increase risk if metastatic cancer or diagnosis within last 3 months), increasing age (risk doubles for each decade over age 40 years), family or personal history of deep vein thrombosis (2-3 x increase risk) and increasing body mass index (2 x increase for BMI > 35 kg/m2 in comparison with BMI