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ANALGESIA

A Randomized Comparison of a Modified Intertendinous and Classic Posterior Approach to Popliteal Sciatic Nerve Block

From the Department of Anesthesiology, Northwestern University Feinberg School of Medicine, Chicago, Illinois.

Address correspondence to Robert J. McCarthy, PharmD, Department of Anesthesiology, 251 E. Huron, F5-704, Chicago, IL 60611. Address e-mail to r-mccarthy{at}northwestern.edu.

Abstract

INTRODUCTION: In this prospective randomized study, we compared a single-injection modified intertendinous (n = 55) with the classic posterior (n = 54) popliteal sciatic nerve block for patients undergoing ankle/foot surgery.

METHODS: Nerve stimulator-guided blocks were performed 7–8 cm (classic posterior) or 12–14 cm (modified intertendinous) above the popliteal crease. Levobupivacaine 0.625% with epinephrine 1:300,000 (Chirocaine®, Purdue Pharma, Stamford, CT), was injected in 5 mL aliquots to a total volume of 0.4 mL/kg (range, 25–35 mL). The needle position was considered acceptable if an evoked motor response of plantar flexion, inversion, eversion or a dorsiflexion of the ipsilateral foot was elicited at 0.4 mA. Complete block was defined as pinprick anesthesia and motor paralysis of the foot within 60 min.

RESULTS: The median distance from the popliteal crease to the modified intertendinous site was 14.0 cm (interquartile range, 13.5–15 cm) compared to 7.5 cm (interquartile range 7.0–8.0 cm) for the classic posterior site (P < 0.01). Complete block was achieved in 44 of 55 patients (81.5%) in the modified intertendinous compared to 39 of 54 patients (70.9%) in the classic posterior group (P = 0.26). Complete block frequency was greater with an evoked motor response of inversion 49 of 56 patients (87.5%) and plantar flexion 23 of 30 patients (76.7%) compared with dorsiflexion/eversion 11 of 23 patients (47.8%) (P = 0.001). The median (95% CI) time (min) to complete block with an evoked motor response of inversion was 10 (0–22 min) for the modified intertendinous compared to 30 (4–56 min) with the classic posterior approach (P = 0.04).

CONCLUSIONS: Potential advantages of the modified intertendinous approach include more rapid onset of anesthesia with an evoked motor response of inversion compared to a classic posterior popliteal sciatic nerve block.