Popliteal Vessels Entrapment by a Variant Accessory Belly of Medial Head of Gastrocnemius

The popliteal fossa is a narrow intermuscular space posterior to the knee joint that is bounded by biceps femoris tendon proximolaterally, semimembranosus muscle proximomedially, and medial and lateral heads of the gastrocnemius muscle distally. The popliteal artery is a continuation of the femoral artery. It begins at the opening (hiatus magnus) in the adductor magnus muscle and runs downward and laterally to terminate at the lower border of popliteus muscle by dividing into anterior and posterior tibial arteries. The popliteal vein is formed at the lower border of the popliteus muscle by the union of veins accompanying the anterior and posterior tibial arteries. It runs upwards and medially and continues as femoral vein at the hiatus magnus. The vein lies superficial to the artery in the popliteal fossa. The gastrocnemius muscle is a superficial muscle of the calf. It has two heads which take their origin from the respective condyles of the femur. The two heads join each other to form a tendon which unites with the tendon of soleus muscle to form the tendo calcaneus. The gastrocnemius is supplied by the tibial nerve and is a plantar flexor of the ankle joint. The popliteal vessels normally course between the medial and lateral heads of gastrocnemius muscle. Because of the variations that occur during embryologic development of the muscles and arteries, the popliteal artery might be entrapped by neighboring muscles and tendons [1]. Stuart described the anatomical basis of popliteal entrapment, having noted the abnormal course of popliteal artery in 64 year old man [2]. Subsequently anatomic variants of popliteal artery entrapment have been described in medical literature: aberrant path of popliteal artery related to the medial or lateral head of the gastrocnemius muscle; compression of a normally positioned artery by variant musculotendinous structures lying between the two heads of gastrocnemius; combination of a displaced artery and muscular variations [3]. Involvement of popliteal vein in the entrapment is uncommon compared to the entrapment of popliteal artery [3]. Aberrant origins and accessory slips are the reported variations of the medial head of the gastrocnemius. The aberrant origin of medial head of the gastrocnemius from the intercondylar notch rather than the medial femoral condyle has been reported. It was found to pass between the popliteal artery and vein before joining the medial head of the muscle [1,4]. In this case report we discuss one of the rare anatomical variations of popliteal vessels entrapment by an accessory belly of the medial head of gastrocnemius.