One of the most commonly affected arteries in arteriosclerosis is the superficial femoral artery. This is the main artery in the thigh, supplying blood to the leg below the knee. A femoro-popliteal bypass graft involves taking blood from the common femoral artery in the groin to the popliteal artery at the knee. Sometimes, this graft can be continued on below the knee and joined to vessels just above the ankle (femoro-distal bypass graft). The best graft involves using the patient’s own long saphenous vein. Because the vein has valves in it, it is necessary to take the vein out, ligating all the branches, and turn it round, inserting the top end into the artery at the knee and the bottom end of the vein into the artery at the groin. An alternative procedure (in situ vein graft) involves separating the long saphenous vein in the groin and separating the long saphenous vein at the level of the knee. All branches are divided between the groin and the knee and then the vein is anastamosed to the artery. A special instrument is used to divide the valves so that blood can flow the wrong way through the vein.