Plantar Flexion Seems More Reliable than Dorsiflexion with Labat???s Sciatic Nerve Block: A Prospective, Randomized Comparison

Abstract

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.

A review of approaches and techniques for lower extremity nerve blocks

“…Although non-randomized studies pertaining to the subgluteal and posterior popliteal approaches have suggested that inversion or plantar flexion should be preferentially sought during neurostimulation, 53,57 only three RCTs (pertaining to the transgluteal and lateral popliteal approaches) have validated this finding. 50,59,60 Ultrasonography, in combination with neurostimulation, has been successfully used as an adjunct in one RCT pertaining to the lateral midfemoral approach. 55 Further RCTs are required to determine its role in other approaches.…”

“…Thus the total anesthesia-related times were not different between the two groups (20-25 min). 49 In 80 patients undergoing hallux valgus surgery, Taboada et al 50 compared plantar flexion (tibial nerve stimulation) to dorsiflexion (peroneal nerve stimulation) as the stimulatory response guiding a single-injection technique. These authors observed a higher success rate with plantar flexion (87.5 vs 55%: P < 0.05).…”

“…Furthermore, the latter also produced shorter onset times for complete sensory and motor block (10 ± 10 vs 20 ± 11 min and 13 ± 10 vs 24 ± 12 min respectively; both P < 0.05). Taboada et al 50 attributed the improved success and onset seen with plantar flexion to the fact that the tibial nerve is the larger of the two sciatic neural components and thus requires more LA to be deposited in its vicinity.…”

A Prospective, Randomised, Double-Blind Comparative Clinical Study of 0.5% Bupivacaine and 0.75% Ropivacaine for Sciatic Nerve Block in Patients Undergoing Elective Below Knee Surgeries

“…Needle placement was considered optimal when maximal plantar flexion of foot was obtained at a current of < 0.5 mA, as plantar flexion of foot has got more success rate than dorsiflexion of foot. 11 After negative aspiration for blood, test solution (20 mL of either 0.5% Bupivacaine or 0.75% Ropivacaine) was injected. Time of completion of injection was taken as time zero.…”

Clinical Efficacy of Sciatic Nerve Block for Below-Knee Orthopaedic Surgeries

“…Needle placement was considered optimal when maximal plantar flexion of foot was obtained at a current of < 0.5 mA, as plantar flexion of foot has got more success rate than dorsiflexion of foot. 12 After negative aspiration for blood, 20 mL of 0.75% ropivacaine was injected. Time of completion of injection was taken as time zero.…”