Vascular GraftingVascular PatencyGraft Occlusion, VascularGastric BypassPolytetrafluoroethyleneFallopian Tube Patency TestsPopliteal ArteryArteriovenous Shunt, SurgicalSaphenous VeinBlood Vessel ProsthesisPeripheral Vascular DiseasesArterial Occlusive DiseasesPeripheral NervesTreatment OutcomeIschemiaBlood Vessel Prosthesis ImplantationVeinsLegLimb SalvageFemoral ArteryTibial ArteriesTime Factors