"Circumferential"(C) spread group will be defined as mepivacaine injectate visualized by ultrasonography all around the median and ulnar nerves imaged in short axis.

Local anesthetic spread will be asymmetrical around the median and ulnar nerves, the mepivacaine will be partially in contact with the nerve

Homogeneous spread of 6 ml of mepivacaine 1% around the median and ulnar nerves in each one using several needle passes and active hydrodissection

Sensory block will be assessed as a loss of cold sensation elicited by a cold wet cotton swab in the areas of the medial and ulnar nerves by comparison with contralateral hand. Sensory block will be clasiffied as follows: 0, anesthesia; 1, hyposthesia; 2, normal sensation. Motor function will be tested as according to a modified Bromage score: 0, no motor blokade; 1, weak response against resistence; 2, complete motor blockade. Motor and sensory blockades will be assessed by a blinded observer at 5, 15, 30 mins after local anesthetic injection and on arrival in the recovery room.

Since the nerve block to the hospital outcome will be registered potencial block-related complications. At the first postoperative day, each patient will be called by phone, to report the time at first onset of pain in the operative site and lack of residual postoperative neurologic symptoms, postoperative nausea and vomiting, and hospital readmission (for severity of pain or bleeding or other reasons)