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A Randomized Comparison Between Subepineural and Conventional Ultrasound-Guided Popliteal Sciatic Nerve Block

Background: This prospective, randomized, observer-blinded trial compared a subepineural sciatic injection at the neural bifurcation (SUB group) and separate postbifurcation injections around the tibial and peroneal nerves. Methods: Ultrasound-guided posterior popliteal sciatic nerve block was carried out in 50 patients. In the group that had separate postbifurcation injections around the tibial and peroneal nerves, the volume of local anesthetic (LA) (30 mL of lidocaine 1%-bupivacaine 0.25%-epinephrine 5 &mgr;g/mL) was divided equally between the tibial and peroneal nerves. In the SUB group, the 2 divisions were identified exactly at the neural bifurcation. In this location, both nerves can still be found inside a common epineural sheath. The entire volume of LA was injected between the 2 branches, inside the common sheath. A blinded observer recorded the success rate (complete sensory block at 30 mins) and onset time. The performance time, number of needle passes, and adverse events were also recorded. Total anesthesia-related time was defined as the sum of performance and onset times. Results: Compared with targeted injections around the tibial and peroneal divisions, a subepineural injection resulted in a higher success rate (84% vs 56%; P = 0.032) as well as improved efficiency (decreased performance/onset/total anesthesia-related times and fewer needle passes; all P ≤ 0.028). In the SUB group, we observed no instance of neural swelling. In 3 subjects randomized to separate injections, sonographic swelling of the tibial nerve occurred after the injection of 2 mL of LA. The needle was carefully withdrawn, and the injection completed uneventfully. In 45 patients, follow-up 1 week after the surgery revealed no sensory or motor deficit. Five subjects were lost to follow-up. Conclusions: Compared with separate injections around the tibial and peroneal divisions, a single subepineural injection at the neural bifurcation provides a higher success rate and requires shorter performance, onset, and total anesthesia-related times. Further studies are required to validate the safety of the subepineural technique.