Minor leg injury a risk factor for blood clot

NEW YORK (Reuters Health) - Common minor injuries to the leg, such as torn muscles and ankle sprains, increase the risk of developing a blood clot in a vein, a condition known as "venous thrombosis," during the ensuing month, according to the results of a large study reported in the Archives of Internal Medicine.

Major injuries that require surgery, a plaster cast, or immobilization are known risk factors for venous thrombosis, Dr. Frits R. Rosendaal and associates at Leiden University Medical Center note in their paper. The contribution of minor injuries that don't require professional treatment is unknown.

Their study included adults having a first episode of deep venous thrombosis in the leg or a lodged in the lungs (pulmonary embolism), a more serious condition. The patients were treated at anticoagulation clinics in the Netherlands between 1999 and 2004.

The investigators excluded cancer patients, surgery patients, those treated with a plaster cast, and individuals on extended bed rest. Subjects in a comparison group (the controls) were partners of the patients and randomly selected individuals from the general population.

The 2,471 patients and 3,534 control subjects completed questionnaires regarding recent injuries, family history, and demographic data. Blood samples or oral swabs were obtained for DNA analysis.

Minor injuries during the previous 3 months were reported by 289 patients (11.7 percent) and 154 of the controls (4.4 percent), although the risk was statistically significant only for leg injuries. Most injuries occurred 1 to 4 weeks prior to recognition of the thrombosis. Specific injuries included rupture of the knee ligaments, sprains of the knee or ankle, and injuries affecting the meniscus of the knee.

For patients with a leg injury and a family history of venous thrombosis, the risk of venous thrombosis was 12-times greater than for subjects without a family history or injury.

Patients with genetic mutations that increased the tendency to form blood clots also had an increased risk. Compared to uninjured subjects without these mutations, the risk in those with a mutation in factor V Leiden was increased by nearly 50-times; and those with a mutation in factor II 20210 plus a leg injury had nearly 9-times the risk of venous thrombosis.

"We believe that many cases of venous thrombosis could be prevented" if high-risk individuals with injuries received a short course of prophylactic treatment, Rosendaal and colleagues conclude.

In a related editorial, Dr. James E. Dalen, at the University of Arizona in Tucson, comments on the need for more research to better diagnose and define the predisposition to thrombosis formation "so that we can determine which patients need prophylactic therapy when they are exposed to risk factors for venous thrombosis, such as surgery, pregnancy, immobility or cancer."

SOURCE: Archives of Internal Medicine, January 14, 2008.