 During embryonic development, the medial head of gastrocnemius migrates medially and superiorly.This migration can cause structural abnormalities, such as irregular positioning of the popliteal artery, and can account for the rare instances of entrapment caused by the popliteus muscle.Less than 3% of all people are born with this anatomical defect that progresses into PAES, and of those who are born with the anatomical defect, the majority never develop symptoms.