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One hundred limbs of 50 non-embalmed cadaveric subjects (mean age of 82) were studied by injection of the venous system of the lower limbs with green neoprene latex. A realistic 3D reconstruction of the whole venous network with an accurate morphological description was obtained by 200 phlebographies and 100 CT venograms. The outlet of the Hunter’s canal, located at the medial aspect of the lower thigh, is narrowed by a tendinous band, the vastoadductor membrane, joining the vastus medialis to the adductor longus. The roof of the canal is made by the vastus medialis muscle, the floor by the adductors, and it is closed medially by the sartorius muscle. A musculotendinous band, the vastoadductor membrane, arose from the adductor magnus muscle, joining the adductor tendon to the vastus medialis. The vascular pedicle being tightened inside this small fibrous space changes its direction to go from the thigh to the popliteal fossa: this explains the frequent kink or plication of the vein, compressed at the posterior aspect of the canal, while the artery is located at the anterior aspect of the canal. The saphenous nerve is located deeply next to the collateral canal and perforates the muscular fascia at the lower third of the thigh. It runs subcutaneously parallel to the tendon of the adductor longus. The femoral vein is located more posteriorly and is frequently narrowed at this level by the edge of the vastoadductor membrane. The reason for venous compression is the reduced width and stiffness of this part of the canal, surrounded by fibrous stiff structures. The vein at this level could be easily compressed in the posterior angle of the hiatus, commonly tightened by a calcified artery. Physiological hypothesis: The cadaveric simulations demonstrated that contraction of the adductor longus closes the hiatus, and contraction of the adductor magnus opens it. During the impulsion phase of the step (extension of the thigh), the systole of the calf muscle pump pushes the blood up into the femoral vein. At this time, the adductor longus is relaxed and the adductor magnus contracts, which opens the Hunter’s hiatus. During thigh flexion, at the beginning of the step (suspension phase), the calf is relaxed and the adductor longus is in tension, which closes the Hunter’s hiatus. This event could be important for the prevention of venous thrombosis of the femoropopliteal axis. In the sitting position, the adductor longus muscle relaxes and the adductor magnus is shortened, which closes the outlet of the Hunter’s canal, leading to venous compression. Different possible derivative routes in case of stenosis of the Hunter’s canal are possible: i) the axial vein located along the ischiatic nerve; ii) the deep femoral vein with a low popliteal communicating branch; iii) the venous arcades of the vastus medialis; iv) and especially the dilated arcades of the semimembranosus muscle. These act like a safety valve, derivating the blood of the popliteal vein to the deep femoral vein, bypassing the Hunter’s canal stenosis. In clinical practice, a venous examination should systematically include an evaluation below the semimembranosus muscle at the posteromedial aspect of the thigh, 10 cm up to the knee joint, close to the midline: the presence of dilated arcades is a sign of stasis, and probably of femoral compression of the Hunter’s outlet.
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