Thrombosis of the popliteal vein.

Among 3,307 consecutive patients (3,556 legs) with deep venous thrombosis, 54 (1.5%) showed an isolated thrombus of the popliteal vein on phlebography. The majority of those had a history of "effort" or long lasting flexion during air or bus travel. Forty-four percent suffered from pulmonary embolism as the first sign of deep venous thrombosis. Functional phlebography demonstrated the primary site of thrombosis at folds forming in the vein wall at flexion. In order to further elucidate the pathogenetic mechanism, 158 popliteal veins were examined phlebographically in different functional states revealing age-related characteristic wall patterns of rings and folds in flexion causing transient impairment of flow. Complementary morphological studies of 120 popliteal veins during autopsy showed a transverse rippling of the vein wall caused by intimal fibrosis and partial atrophy of the media corresponding to the phlebographic findings. It is concluded that microtrauma during effort in combination with impaired venous backflow and fibrotic transformation of the venous wall can lead to thrombus formation in the popliteal vein.