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

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 (R), Purdue Pharma, Stamford, CT), was injected in 5 mL aliquots to a total volume of 0.4 mL/kg (range, 25-35 L. 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.