Inclusion Criteria:  Man or woman over 18 (under effective contraception, hormonal contraceptive or intrauterine device, if premenopausal). Patient with critical ischemia of the lower limb (stage 4-5-6 according to the Rutherford classification) requiring revascularization by sub-gonal bypass Patient eligible and scheduled for bypass in venous allograft stored at + 4 ° C with distal anastomosis below the knee Patient without usable autologous great Saphenous vein Subject affiliated or beneficiary of a social security scheme Patient having received the appropriate information concerning the objectives and procedures of the study and having declared his non-objection.  Exclusion Criteria:  Use of unscheduled allografts Patient requiring composite bypass in AGV + autologous venous material or prosthesis Patient requiring replacement of infected prostheses Patient with acute ischemia Patient with severe coagulation disorders Patient classified physical status score 4 Patient participating in another clinical trial Potential allergy to the graft Protected patients: Adults under guardianship, curatorship or other legal protection, deprived of their liberty by judicial or administrative decision Pregnant or breastfeeding woman