Which part of the leg is associated with an increased risk of pulmonary embolism?

The thigh is associated with an increased risk of pulmonary embolism due to the presence of larger and deeper venous structures that can form thrombi. Venous thrombosis often occurs in the deep veins of the thigh, particularly in conditions that promote venous stasis, endothelial injury, or hypercoagulability, collectively known as Virchow's triad. When a thrombus forms in the deep veins of the thigh, it can dislodge and travel through the venous system to the right side of the heart and into the pulmonary arteries, leading to a pulmonary embolism.

In contrast, while thrombi can also occur in the calf, they are more commonly associated with less severe embolic events and do not typically have the same degree of systemic impact as those forming in the thigh. The foot and hip areas also do not have the same anatomical conditions that predispose patients to a higher risk of significant venous thromboembolism. Thus, complications from thrombi in the thigh make it the area most critically associated with the risk of pulmonary embolism.