Minor injuries as a risk factor for venous thrombosis.

BACKGROUND Injuries increase the risk of venous thrombosis. So far, most research has focused on major injuries that are accompanied by other risk factors for venous thrombosis, such as plaster casts and surgery. We studied the association of venous thrombosis with common minor injuries, such as minor sural muscle ruptures and ankle sprains. METHODS We performed a large, population-based, case-control study (the Multiple Environmental and Genetic Assessment of risk factors for venous thrombosis [MEGA] study), including consecutive patients with a first deep venous thrombosis of the leg or pulmonary embolism and control subjects. Participants with malignant neoplasms, those who underwent surgery, and those who had a plaster cast or extended bed rest were excluded. RESULTS Of 2471 patients, 289 (11.7%), and of 3534 controls, 154 (4.4%) had a minor injury in the 3 months preceding the venous thrombosis (patients) or completion of the questionnaire (controls). Venous thrombosis was associated with previous minor injury (odds ratio adjusted for sex and age, 3.1; 95% confidence interval, 2.5-3.8). The association was strongest for injuries that occurred in the 4 weeks before thrombosis and was not apparent before 10 weeks. Thrombosis was more strongly associated with minor injuries located in the leg (odds ratio adjusted for sex and age, 5.1; 95% confidence interval, 3.9-6.7), while those located in other body parts were not associated. A 50-fold increased risk was found in factor V Leiden carriers with a leg injury compared with noncarriers without injury (odds ratio, 49.7; 95% confidence interval, 6.8-362.7). CONCLUSIONS Minor injuries in the leg are associated with greater risk of venous thrombosis. Because minor injuries are common, they could be major contributors to the occurrence of venous thrombosis.