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].

The investigators propose to make a comparative trial between levobupivacaïne 0.5% ropivacaine and 0.5% under the control of the ultrasound as part of a sciatic nerve block. The use of ultrasound will reduce the variability of results because the changes would be linked exclusively to the local anesthetic. The investigators test the hypothesis that levobupivacaïne gives better results in terms of onset of action than ropivacaine.

Inclusion Criteria:

• Patients with unilateral major surgery of the foot: hallux valgus (not ambulatory), claw toes, fusion-Astragalo calcaneum, complex syntheses of tarsus-aged over 18 years .
• Male and female
• ASA 1 or 2
• Insured Social
• Informed Consent

Exclusion Criteria:

• Diabetes
• Intoxication-alcoholic chronic
• Allergy to local anesthetics
• Hemostasis disorders
• Hepatic failure
• Chronic pain syndrome