Ultrasound Guidance Improves the Success of Sciatic Nerve Block at the Popliteal Fossa

Abstract

Real time ultrasound guidance is a recent development in the area of peripheral nerve blockade. There are limited data from prospective randomized trials comparing its efficacy to that of traditional nerve localization techniques. In the present study, we tested the hypothesis that ultrasound guidance improves the success rate of sciatic nerve block at the popliteal fossa when compared with a nerve stimulator-guided technique. After Institutional Research Ethics Board approval and informed consent, 74 patients undergoing elective major foot or ankle surgery were randomly assigned to receive a sciatic nerve block at the popliteal fossa guided by either ultrasonography (group US, transverse view, needle in plane approach above the sciatic nerve bifurcation), or nerve stimulation (group NS, single injection, 10 cm proximal to the knee crease). A standardized local anesthetic admixture (15 mL of 2% lidocaine with 1:200,000 epinephrine and 15 mL of 0.5% bupivacaine) was used. Sensory and motor function was assessed by a blinded observer at predetermined intervals for up to 1 hour. Block success was defined as a loss of sensation to pinprick within 30 minutes in the distribution of both tibial and common peroneal nerves. Group US had a significantly higher block success rate than group NS (89.2% vs. 60.6%, P = .005), while the procedure time was similar. Ultrasound guidance enhances the quality of popliteal sciatic nerve block compared with single injection, nerve stimulator-guided block using either a tibial or peroneal endpoint. Ultrasound guidance resulted in higher success, faster onset, and progression of sensorimotor block, without an increase in block procedure time, or complications.