Blood flow to the legs is carried through the aorta, the main artery of the body.  At about the level of the navel, the aorta divides like a "Y" into the left and the right  iliac arteries. As the iliac arteries travel into the groin area they are renamed the  femoral arteries; each femoral artery in turn travels down the thigh and passes behind the knee, where its name changes to the popliteal  artery.

The femoral and popliteal arteries are common sites for the build-up of plaque and the development of arterial blockage (stenosis), leading to the onset of a symptom called leg claudication, in which painful muscle cramps occur during walking.  If the condition goes untreated, circulation to the leg can become so poor that the patient experiences constant pain and coldness of the feet, or even open sores and gangrene.  Medication, moderate exercise, and elimination of smoking will often relieve the symptoms, but if not, surgery becomes necessary.

Vascular surgeons are able to restore blood flow to the legs by performing arterial bypass procedures.  A femoral-popliteal bypass is performed by implanting a small tube to carry blood flow from the femoral artery in the groin directly to the popliteal artery near the knee, bypassing the blocked sections of the femoral artery.  Ideally this bypass tube ("graft") will be made from the patient's own leg veins, usually the saphenous vein, which is part of a network of veins located in the fatty tissue under the skin.  Occasionally the surgeon will need to borrow veins from the other leg, or even the arms.  If no veins are available, a special type of plastic tube can be used instead. 

Femoral-popliteal bypass is a major surgical procedure requiring several days in the hospital and several weeks of recovery.  If performed by well-trained and properly qualifed vascular surgeons, it has a high success rate in relieving the symptoms of poor circulation, improving walking ability, and even saving legs that might otherwise face amputation.