Comparison of the parasacral approach and the posterior approach, with single- and double-injection techniques, to block the sciatic nerve

Background: The purpose of this study was to compare parasacral and Winnie's single- or double-injection approaches for sciatic nerve block. Methods: One hundred fifty adults scheduled to undergo lower limb surgery were randomized to receive on the sciatic nerve 20 ml ropivacaine, 0.75%: single bolus for parasacral and Winnie's single injection. For Winnie's double injection, the peroneal and tibial nerves received separately 10 ml plus 10 ml. Blocks were performed with the use of nerve stimulator (intensity < 0.5 mA, 1 Hz). For the parasacral method, a line was drawn between the posterior superior iliac spine and the ischial tuberosity; needle entry was at 6 cm inferior to the posterior superior iliac spine. Results: The groups were similar. Time to perform the block was 2 (1-5) min for the parasacral method, with no difference from Winnie's single injection (3 [1-10] min), but was shorter with double injection (5.5 [2-15] min) (P = 0.0001). Onset of sensory block was similar in the parasacral (25 [7.5-50] min) and Winnie single-injection groups (25 [5-50] min) but significantly longer in the double-injection group (15 [5-50] min). Success rates for complete block were similar in the parasacral (66%) and Winnie's double-injection groups (68%) after 30 min but higher in the Winnie's single-injection group for tibial sensory and motor block (48%) (P < 0.017). Conclusion: Time to perform a parasacral block was short, and the parasacral approach had a high success rate and a short onset time. Therefore, this block might be a useful alternative to Winnie's modification for sciatic nerve block.