A person who has a common minor leg injury, such as an ankle sprain or a muscle rupture has a higher risk of developing a blood clot in his/her leg or lung, according to an article in Archives of Internal Medicine (JAMA/Archives), Januray 14th issue.

Previous studies had demonstrated that the risk of venous thrombosis is higher for those with major injuries, the authors explain. The disorder includes DVT (deep vein thrombosis) or blood clots in the leg, or blood clots that travel to the lungs (pulmonary embolism). "However, apart from the injury itself, other risk factors for venous thrombosis will be present because of the major injury, such as surgery, a plaster cast, hospitalization and extended bed rest. The risk of so-called minor injuries that do not lead to these additional factors is unknown."

Karlijn J. van Stralen, M.Sc., Leiden University Medical Center, Leiden, the Netherlands, and team look at 2,471 patients who had developed venous thrombosis between 1999-2004. The participants filled in a questionnaire about any injuries, surgical procedures, plaster casts or immobilizations they had within 12 months of developing blood clots. They also wrote down their weight, height, family history, and sports participation. They were compared to 3,534 others (controls) who didn't have venous thrombosis. The controls were recruited by inviting the partners of the patients to take part in the study - a random-digit-dialing method was also used to recruit controls.

The researchers found that 11.7% (289) of the patients had had a minor injury during the three months leading up to the development of venous thrombosis, while 4.4% (154) of the controls had a minor injury in the three months before completing the questionnaire.

The researchers wrote "Minor injuries that do not require surgery, a plaster cast or extended bed rest were associated with a three-fold greater relative risk of venous thrombosis. The association appeared local because injuries in the leg were associated strongly with thrombosis, while injuries in other locations were not associated with thrombosis. The association was strongest for injuries that occurred in the month before the venous thrombosis, suggesting a transient effect."

The link was stronger among people who had a genetic or other risk factor for blood clots, the researchers report.

The authors believe there may be several reasons why such injuries might raise the risk of blood clots. Even a less serious injury that does not immobilize the patient may still cause him/her to be less active - inactivity in itself raises the risk of blood clots. Add to this any damage to the blood vessel wall caused by an injury and the risk of clotting in the affected area grows more still.

The researchers conclude "Because minor injuries are common, they can be major contributors to the occurrence of venous thrombosis. Many individuals with minor injuries will have contacted the general practitioner first. Therefore, there may be an important task for general practitioners to identify subjects who are at high risk of developing venous thrombosis and subsequently to provide prophylactic measures."

Arch Intern Med. 2008;168[1]:21-26.
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- Christian Norqvist

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