The accessory saphenous vein is linked to the greater saphenous vein, which runs parallel to it, and is located in the leg and thigh. The greater saphenous vein is a large superficial (near the skin’s surface) vein that originates where the foot's dorsal venous arch merges with the big toe's dorsal vein. It travels up the leg's medial side (closer to the middle) after passing anteriorly to the medial malleolus, a bony projection on the inside of each ankle. The accessory saphenous vein joins it immediately before it drains into the femoral vein.
When the accessory saphenous vein reaches the knee, it travels posteriorly along the inner parts of the knee and thigh and finally across the posterior border of the femur bone's medial epicondyle, a rounded bony projection at the lower (distal) end of the femur where it connects to the knee. The accessory saphenous vein then travels to the thigh's front surface before entering the saphenous hiatus, an oval-shaped opening in the fascia lata of the thigh. The fascia lata is a layer of fibrous connective tissue that envelops the thigh muscles. The vein then attaches to the femoral vein in the saphenofemoral junction of the femoral triangle. The femoral triangle is a depression in the upper part of the inner thigh that contains the femoral nerve, artery, and veins as well as lymph nodes and vessels.
The greater accessory saphenous vein branches out into smaller veins that are made of elastic fiber. These veins have diminished muscle cells and thin walls. They are often the cause of varicose veins, which develop when they dilate.