Bypass surgery may be done to treat arteries that are narrowed or blocked. In this procedure, blood is rerouted around the affected artery—for example, around part of the femoral artery in the thigh or part of the popliteal artery in the knee. A graft consisting of a tube made of a synthetic material or part of a vein from another part of the body is joined to the blocked artery above and below the blockage.