When medical treatments fail, critical ischemia of the lower limb often leads to surgery, i.e. above knee femoro popliteal bypass. This bypass can be performed either with DACRON or PTFE prosthesis or with the autologous saphenous vein. Both technics are used but they have not been compared regarding bypass permeability and limb salvage. Thus, this study will compare the permeability rate of above knee femoro popliteal surgery whether performed with autologous vein versus prosthesis