Ultrasound-Guided Popliteal Block Distal to Sciatic Nerve Bifurcation Shortens Onset Time

Abstract

Popliteal sciatic nerve block (SNB) in combination with saphenous nerve block provides anesthesia and analgesia for foot and ankle surgeries. Landmark-based and image-guided techniques, to date, aim at blocking the sciatic nerve proximal to its bifurcation. Sciatic nerve block is usually associated with a long onset time (30-60 mins). We hypothesized that SNB distal to its bifurcation (blocking its 2 main branches tibial and common peroneal nerves separately) is associated with a shorter onset time than blockade proximal to its bifurcation. Fifty patients scheduled for major elective foot or ankle surgery were randomly allocated to receive ultrasound-guided SNB 5 cm proximal to (group P) or 3 cm distal to (group D) its bifurcation in the popliteal fossa. Thirty milliliters of a standardized local anesthetic solution of equal volumes of 2% lidocaine and 0.5% bupivacaine with 1:200,000 epinephrine was used. Sensory and motor assessments were performed every 5 mins by a blinded observer until complete sensory and motor blockade developed in both tibial and common peroneal nerve territories. All patients in both groups developed a complete block. Patients in group D presented a 30% shorter onset of both sensory (21.4 [SD, 9.9] vs 31.4 [SD, 13.9] mins) (P = 0.005) and motor block (21.5 [SD, 11.3] vs 32.4 [SD, 14.9] mins) (P = 0.006) than patients in group P. Procedure time, procedure-related discomfort, and patient satisfaction were similar in both groups. Our data suggest that popliteal SNB distal to the bifurcation has a shorter onset time than SNB proximal to its bifurcation, and therefore, it may be a good option when a fast onset for a surgical block is required.