Minor Leg Injuries Also Pose Clot Risk

By Charles Bankhead
LEIDEN, The Netherlands, Jan. 14 -- Sprains, bruises, and other minor leg injuries triple the risk of venous thrombosis within three months, investigators here found.
Among almost 2,500 patients with venous thromboembolism, 11.7% had a recent history of minor leg injuries compared with 4.4% of a matched control group without VTE, Frits R. Rosendaal, M.D., Ph.D., of the University of Leiden, and colleagues reported in the Jan. 14 issue of Archives of Internal Medicine.
Risk of venous thrombosis was greatest in the first four weeks after injury, they said.
"The risk of venous thrombosis was threefold increased, resulting in a population-attributable fraction of 7.9%," the researchers said.
Venous thrombosis affects up to three individuals per 1,000 annually, they noted. Known risk factors include surgery, immobility, and prothrombotic genetic variants. Major injuries are known to increase the risk, but the association with minor injuries had not been studied carefully, they said.
So the researchers prospectively evaluated causes of venous thromboembolism in the Multiple Environmental and Genetic Assessment (MEGA) of risk factors for venous thrombosis study.
From March 1999 through August 2004, investigators at six anticoagulation clinics enrolled patients with a first episode of venous thromboembolism, including deep vein thrombosis in the leg and pulmonary embolism.
The study included 2,471 patients and 3,534 matched controls ages 18 to 70. Information for the study was obtained from patient self-reports, hospital records, and primary care physicians. The data collected included the most recent injury before the embolism and specifically addressed minor injuries.
The investigators determined that 289 (11.7%) of the patients and 154 (4.4%) of the controls had sustained minor injuries in the preceding three months. After adjustment for age and sex, the between-group difference translated into an odds ratio of 3.1 for recent minor injury in the venous thromboembolism patients.
The difference was attributable entirely to minor injuries in the leg (OR: 5.1, 95% CI: 3.9 to 6.7). Minor injuries in other parts of the body had no association with thromboembolism.
Factor V Leiden carriers with a minor leg injuries had a 50-fold increased risk of thromboembolism compared with noncarriers (OR: 49.7, 95% CI: 6.8 to 362.7).
Because clots were not associated with injuries in areas of the body other than the leg, the researchers ruled out systemic prothrombotic reaction as an explanation for the increased risk.
They also excluded patients requiring extended immobilization or bed rest. However, they acknowledged that even minor injuries might lead to reduced mobility short of bed rest and thus predispose a patient to venous thromboembolism.
Edematous vein obstruction might result in venous stasis, the authors allowed. They also suggested that minor injury might damage a blood vessel wall, thereby increasing the risk of clot formation.
The investigators wrote that they doubted recall bias for minor injuries among patients more than controls because patients reported leg injuries when they had a pulmonary embolism and not just venous thrombosis, but they could not exclude recall bias entirely.
The findings have implications for primary care physicians, the authors noted.
"Many individuals with minor injuries will have contacted the general practitioner first," they noted. "Therefore, there may be an important task for general practitioners to identify subjects who are at a high risk of developing venous thrombosis and, subsequently, to provide prophylactic measures."
The study was supported by the Netherlands Heart Foundation, the Dutch Cancer Foundation, and the Netherlands Organization for Scientific Research.
The authors reported no potential conflicts.
Primary source: Archives of Internal MedicineSource reference:Van Stralen JK, et al "Minor injuries as a risk factor for venous thrombosis" Arch Intern Med 2008; 168: 21-26.