David Beckhams of the world, Mafia snitches who get their kneecaps broken and even folks prone to whacking their legs on inanimate objects have one more thing to worry about. Injuries to the leg may increase the risk of blood clots.
In a study of 2,471 patients diagnosed with either deep venous thrombosis (a blood clot in the leg) or pulmonary embolism (a clot that has traveled to the lung), researchers at Leiden University Medical Center in the Netherlands found that 11.7% had had a minor leg injury in the three months before the diagnosis.
This represents a threefold increase in risk relative to the control group, writes senior author Dr. Frits Rosendaal in an e-mail.
Those in certain high-risk groups for venous thrombosis, such as people with a family history of the disorder or a genetic predisposition, were especially vulnerable to forming a blood clot in the wake of a leg injury. "Indeed, the latter group has a 50-fold increased risk," says Rosendaal, a professor of clinical epidemiology at Leiden University Medical Center.
This is intriguing information for physicians who work with leg injuries and vascular surgeons charged with diagnosing DVT.
"We've all seen patients in our practices who develop a deep vein thrombosis after minor injuries," says Dr. Leonardo Clavijo, director of vascular medicine for USC, "but we never had a study to support some of these clinical observations."
Deep vein thrombosis occurs in about one to two people per 1,000 each year. Of those, an estimated 1% to 5% will die from complications, most notably a pulmonary embolism. When the clot blocks a pulmonary artery (impairing circulation), the blood loses oxygen, severely straining the heart. That can lead to many complications, including heart failure.
People most at risk for DVT are those who've been on prolonged bed rest or otherwise unable to move their legs frequently, such as hospital patients, stroke victims and people with spinal cord injuries. Frequent movement of the leg muscles helps keep blood flowing through the veins.
Other risk factors include advanced age, obesity, recent surgery, congestive heart failure, leg or hip fractures and the existence of a clotting disorder.
There are several reasons that leg injuries could increase the risk of blood clots, the authors note in the study, which appears in the Jan. 14 issue of Archives of Internal Medicine. Even minor injuries could cause an individual to be inactive for a period, which could increase susceptibility to blood clots. Another possibility is that damage to the blood vessel increases clotting risk in the affected area.
One physician who has seen hundreds of cases of venous thrombosis cautions, however, against putting too much weight on the risks caused by minor injuries.
"I'm not convinced based on a single study that there truly is a connection," says Dr. Peter Lawrence, a vascular surgeon and director of UCLA's Gonda Vascular Center. Lawrence estimates that the center performs 4,000 to 5,000 ultrasounds a year for patients with vascular diseases.
Of particular concern, he says, is the study's questionnaire format, in which venous thrombosis patients and a control group were asked about their recollections of previous injuries. Lawrence believes that thrombosis patients will scour their memories to make a connection, whereas healthy people will tend to gloss over previous scrapes and dings.
Venous thrombosis is a silent disease with potentially deadly consequences.
"About half of patients with venous thrombosis have no signs," Lawrence says. Those who have symptoms generally experience an ache in the leg. "They may experience pain when they move the extremity," he says, "particularly when they move the muscles that are adjacent to the vein that's clotted." The nature of the pain varies from person to person.
Many disorders can mimic deep vein thrombosis, including a ruptured muscle, shin splints and a Baker cyst, characterized by fluid in the knee joint protruding from the back of the knee. Fortunately, venous thromboses are fairly easy to diagnose with ultrasound, and serious clots can be treated with anticoagulants such as heparin and coumadin.
The findings are important for high-risk patients, USC's Clavijo says. "If you have someone with prior DVT, a strong family history of blood clots, and they have a minor injury accompanied by symptoms that are unusual or out of proportion to the injury, or they develop shortness of breath, then they should be seen by a physician promptly."
Clavijo is not suggesting that the at-risk population be put on blood thinners as a cautionary measure, but believes they should be evaluated with DVT in mind. "Primary-care doctors, ER doctors and orthopedic surgeons need to be aware of it because they are first-line providers for these patients."