the main venous trunks of the lower limbs
Generally, incompetence of the main venous trunks called great saphenous vein and small saphenous veins are responsible for the most part of the varicose veins.
These veins are often invisible because they’re subcutaneous and can be as deep as 2 cm under the skin.
Great saphenous vein
The great saphenous vein is a superficial blood vessel that runs up on the inside of the leg from the ankle to the groin.
Small saphenous vein
The small saphenous vein is a shorter superficial blood vessel that goes up from the heel to the back of the knee, sometimes even higher up to the back of the thigh.