What Can Cause Leg Swelling Below the Knee?

Swelling centred on the knee after twisting, impact, or a sudden change of direction can accompany injury to structures such as the meniscus or a ligament. A soft fullness behind the knee may occur with a Baker's cyst, which can form when excess joint fluid pushes into a sac at the back of the joint. Gout and bursitis can cause a tender, warm, swollen area, while osteoarthritis may produce recurring swelling with stiffness.

Swelling extending through the calf, ankle, or foot calls for a broader assessment because fluid can collect outside the knee joint. Whether one or both legs are affected, and whether redness, heat, breathlessness, recent immobility, wounds, or medicines are involved, helps guide the evaluation.

Compare both legs and note when swelling began, exactly where it sits, whether an injury occurred, and whether the area is warm or discoloured. Reduce activities that aggravate an injured knee and avoid forceful massage of an unexplained swollen calf. A clinician may examine the joint, skin, circulation, and calf; imaging, blood tests, or removal of joint fluid may be considered when the examination points to a specific cause.

Get urgent medical help for sudden swelling in one leg with calf pain, warmth, or redness, especially if it follows reduced mobility. Call emergency services if leg swelling occurs with chest pain, breathlessness, coughing blood, fainting, or severe weakness. Prompt assessment is also needed for fever with a hot, very painful joint, rapidly spreading redness, a cold or blue foot, or inability to bear weight after injury.

Ask whether the fluid appears to be inside the knee joint or in the surrounding leg, whether circulation needs checking, and which movements are appropriate. If aspiration is proposed, ask whether it is intended to relieve pressure, examine the fluid, or both.