Ropivacaine 0.5% and 0.5% in levobupivacaïne are used in regional anesthesia for major surgery of the foot. The literature does not highlight a significant difference in terms of onset of action between these two molecules to block the sciatic nerve [4]. Our hypothesis is that this lack of difference is due to the use of a neurostimulator for locating the injection site (indiscriminate nature of the anatomical approach to the sciatic nerve). Indeed, the sensitivity of neurostimulation is low compared with ultrasound [58] and ultrasound, for accurate visualization of the deposit of the local anesthetic around the nerve to improve the quality of the block and reduce the onset of action of local anesthetic [46, 47].