Severe pain due to leg, ankle or foot trauma do not beneficiated of a simple loco regional anaesthesia technic. Loco regional anesthesia is superior to intravenous morphine for treating severe pain and specially during transportation and mobilization of the patient. The purpose of the study is to assessed a new technic of blind sciatic nerve block in the popliteal fossa in the pre hospital setting compared to the intravenous morphine. The blind technic is a modified technic of the classic sciatic nerve block with nerve stimulation.