Edema (leg swelling) may affect both legs equally or may be more of a problem in one leg. The causes of swelling in one leg may be similar to the other leg, but it is not unusual for different factors to cause the swelling in each leg. Frequently, leg swelling is caused by more than one factor such as venous insufficiency, obesity, and previous saphenous vein harvest for heart bypass surgery.
Swelling may occur due to high pressure in the veins of the legs, local injury, inflammatory changes, obstruction of lymphatic fluid outflow, infection, low blood protein levels, obesity, pregnancy, fluid retention states, or drug effects. High pressure in the veins of the legs results in fluid, proteins, and blood cells leaking through the wall of small veins into the soft tissues, especially near the ankles. This causes pitting edema, swelling which will leave a temporary indentation in the skin with pressure from a shoe, sock, or intentional pressure such as a squeeze with a finger. Some of the causes of leg edema due to elevated venous pressures include:
Localized swelling may be due to trauma, hematoma (collection of non-flowing blood in the soft tissue), infections, fracture, superficial thrombophlebitis (clots in veins of the fatty tissues), rupture of a tendon or muscle, cyst at a joint (such as a synovial cyst at the knee), and, sometimes, spontaneous bleeding into the tissue due to a ruptured blood vessel.
Chronic leg swelling may also be due to states that result in generalized body fluid expansion which may be more apparent in the legs due to the effect of gravity such as:
Some of the most common medications which cause leg swelling are non-steroidal anti-inflammatory drugs taken for pain relief or for arthritic discomfort and calcium channel blockers taken for heart disease or hypertension. Some of the more common drugs which may cause swelling in some individuals include:
Cellulitis, infection of the skin and fatty tissues of the leg may cause swelling with pain and tenderness. Pain from cellulitis may be very severe or may manifest as tenderness and mild pain with faintly pink to bright red skin.
Swelling of the foot, especially if the skin does not pit with brief application of pressure, may be due to lymphedema, a failure of the microscopic network of channels which move tissue fluid from the extremity back to the blood stream at the level of the upper chest. Some of the causes of lymphedema include:
After venous insufficiency, obesity is the next most common cause of lower extremity swelling in the United States. Abdominal obesity partially obstructs venous outflow and lymphatic outflow from the legs. Obesity also accelerates the stretching of the leg veins due to the effects of gravity, thus contributing to the progression of venous insufficiency.
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