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DVT and VTE occur with increased frequency after surgery or trauma. No one knows exactly how often they occur, because various studies have found incidences ranging from a few percentages to 70% in people with various high-risk conditions.
Many things affect the probability that you will develop deep venous thrombosis. Clotting is thought to occur as a result of three factors, trauma, stasis or blood slugging, and the body’s particular tendency toward clotting. The location of the surgical or accidental trauma is one of the most significant factors in the development of a DVT. The closer to the torso that the surgery or trauma is, the more likely that dangerous deep venous thrombosis will occur. Stasis is the lack of flow of blood through the veins. The more that the blood pools, the easier it is to interact with the proteins within the vein walls that initiate clotting. Braces, casting and lack of movement after surgery or trauma promote clotting by reducing muscle activity, an important method of pumping blood back to the body.
Medications that thin the blood are routinely prescribed to prevent clotting after high risk operations such as hip or knee replacement. In foot and ankle surgery, the reported incidence is much lower (0.22%) and therefore blood-thinning medications after foot and ankle surgery are not recommended (reference). No relationship has been shown between DVT risk and age, weight, diabetes mellitus, history of previous DVT, or any other medical condition in foot and ankle surgery. These have been described as risk factors for DVT after high-risk surgery. The only risk factor for DVT in foot and ankle surgery is immobilization and restricted ambulation after the surgery, which increased the risk to 0.45%
Unfortunately, blood clots are difficult to detect without sophisticated tests. Common signs are unusual swelling and pain in the calves, but this is also common after surgery and trauma without blood clots. Most people that develop them have no unusual symptoms. Ultrasound tests can detect some blood clots when symptoms suggest it may be present. Bruising and redness around the wound, calf or ankle is not a sign of deep venous thrombosis, but it is a sign of bleeding and inflammation under the skin, which is almost always present after surgery and is not usually dangerous.
Depending on your risks, your doctor may recommend certain preventative treatment. Early ambulation to the extent that is possible and motion of the foot and ankle is nearly always a good idea. Mechanical devices that squeeze the foot or calf may also be ordered, but are usually only practical in the hospital. Foot pumping exercises are often recommended (figure).
In addition, certain medications, some taken by mouth and others injected, may be recommended. The oral medication, warfarin (Coumadin), must be monitored by regular laboratory tests to measure its effect on clotting. Aspirin is sometimes suggested, but there is controversy over whether it is effective for preventing the most dangerous types of VTE. Other injectable medications are sometimes prescribed including enoxaparin (Lovenox) and fondaparinux (Arixtra). These medications are typically given for three weeks for the prevention of blood clots after surgery, but the ideal length of time necessary is not known. These medications do have some risks including bleeding, increased wound problems, allergic reactions, and, rarely, more serious side effects including bleeding into the brain and clotting disorders. There may also be a considerable cost for the medication or the laboratory tests used to monitor the medication.
Figure. Calf pumps. Calf pumping exercises use the body’s musculature to express blood through the veins to avoid stasis. These exercises may help prevent blood clots in the leg after surgery or trauma and have been shown helpful during plane flights.
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