Figure 12. Drawings illustrate the classification scheme for PAES. In type I, the medial head of the gastrocnemius muscle is normal, and the popliteal artery is displaced medially around and beneath the muscle. In type II, the medial head of the gastrocnemius muscle arises from an abnormal lateral position. The popliteal artery descends normally but passes medial to and beneath the muscle. In type III, the popliteal artery is compressed by an abnormal slip of gastrocnemius muscle. In type IV, the popliteal artery is entrapped by a fibrous band or by the popliteus muscle. Type V is any of the four preceding types that includes the popliteal vein, and type VI is functional PAES (normal anatomy).