Ultrasound-Guided Popliteal Block Distal to Sciatic Nerve Bifurcation Shortens Onset Time A Prospective Randomized Double-Blind Study

Background and Objectives: 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. Methods: 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. Results: 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. Conclusions: 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.