Background: Evidence indicating that single- and double-injection techniques for inducing a sciatic nerve block via a posterior subgluteal approach yield a similar success rate prompted us to investigate whether the two anesthetic techniques yield a similar success rate via a lateral approach. We also hypothesized that, owing to the peculiar anatomic features of the sciatic nerve at the popliteal level, a single injection via the lateral approach might induce effective anesthesia by targeting the tibial nerve only.
Methods: Ninety-six patients undergoing popliteal sciatic nerve block via a lateral popliteal approach for foot surgery were randomized to receive a single 30-ml injection of ropivacaine 7.5 mg/ml to block the tibial nerve (TN group, n= 32) or the common peroneal nerve (CPN group, n= 32), or two separate 15-ml injections (TN + CPN group, n= 32), after stimulation to evoke motor responses from the target nerves.
Results: The mean time to obtain a complete sensory blockade (surgical anesthesia) was shorter in the TN group than in the CPN and TN + CPN groups (14 +/- 7 min vs. 23 +/- 17 and 21 +/- 14 min, respectively; P < 0.05). The success rate was similar in the TN and TN + CPN groups (94%) and, 25 min after the initial injection, was already better in these groups than in the CPN group (94% vs. 75%; P < 0.05).
Conclusions: A lateral popliteal sciatic nerve block obtained with a single 30-ml injection of ropivacaine 7.5 mg/ml after electrostimulation to locate the tibial nerve is as effective as multiple TN + CPN stimulation and injection, and local anesthesia has a significantly shorter onset time.