A New Anterior Approach to the Sciatic Nerve Block

Background: Although several anterior approaches to sciatic nerve block have been described, they are used infrequently. The authors describe a new anterior approach that allows access to the sciatic nerve with the patient in the supine position.

Method: Sciatic nerve blocks were performed in 22 patients. A line was drawn between the inferior border of the anterosuperior iliac spine and the superior angle of the pubic symphysis tubercle. Next, a perpendicular line bisecting the initial line was drawn and extended 8 cm caudad. The needle was inserted perpendicularly to the skin, and the sciatic nerve was identified at a depth of 10.5 cm (9.5-13.5 cm; median and range) using a nerve stimulator and a 15-cm b-beveled insulated needle. After appropriate localization, either 30 ml mepivacaine, 1.5% (group 1 = knee arthroscopy; n = 16), or 15 ml mepivacaine, 1.5%, plus 15 ml ropivacaine, 0.75%, (group 2 = other procedures; n = 6) was injected.

Results: Appropriate landmarks were determined within 1.3 min (0.5-2.0 min). The sciatic nerve was identified in all patients within 2.5 min (1.2-5 min), starting from the beginning of the appropriate landmark determination to the stimulation of its common peroneal nerve component in 13 cases and its tibial nerve component in 9 cases. A complete sensory block in the distribution of both the common peroneal nerve component and the tibial nerve component was obtained within 15 min (5-30 min). A shorter onset was observed in patients who received mepivacaine alone compared with those who received a mixture of mepivacaine plus ropivacaine (10 min [5-25 min]vs. 20 min [10-30 min];P< 0.05). Recovery time was 4.6 h (2.5-5.5 h) after mepivacaine administration. The addition of ropivacaine produced a block of a much longer duration 13.8 h (5.2-23.6 h);P< 0.05. No complications were observed.