Plantar flexion seems more reliable than dorsiflexion with Labat's sciatic nerve block: A prospective, randomized comparison

Labat's classic approach to the sciatic nerve has not been able to show which motor response of the foot provides a more frequent rate of complete sensory and motor block. In this prospective, randomized, double-blind study, we compared plantar flexion with dorsiflexion with regard to onset time and efficacy of sciatic nerve block using the classic posterior approach. A total of 80 patients undergoing hallux valgus repair were randomly allocated to receive sciatic nerve block after evoked plantar flexion (n = 40) or dorsiflexion (n = 40). Twenty milliliters of 0.75% ropivacaine was injected after the motor response was elicited at <0.5 mA. Success rate was defined as complete sensory and motor block in all sciatic nerve distributions associated with a pain-free surgery. Time required for onset of sensory and motor block of the foot was recorded. Success was more frequent after elicited plantar flexion (87.5%) than dorsiflexion (55%; P < 0.05). Onset of complete sensory and motor block of the foot was faster after elicited plantar flexion (10 ± 10 min and 13 ± 10 min, respectively) compared with dorsiflexion (20 ± 11 min and 24 ± 12 min; P < 0.05). We conclude that plantar flexion of the foot predicts a shorter onset time and a more frequent success rate than dorsiflexion with Labat's classic posterior sciatic nerve block.