Title: A Prospective Comparison between the Classic Labat and a Higher Intermuscular Approach to Popliteal-Sciatic Block
Nicole Higgins, M.D., Antoun Nader M.D., Mark C. Kendall M.D., Radha Sukhani M.D., Robert
McCarthy PharmD.
Northwestern University Feinberg School of Medicine, Chicago, Illinois

Introduction: A limitation to the classic Labat approach to popliteal-sciatic nerve block is the identification of the block site by surface landmarks that are fixed measurements from the knee crease and midline of the popliteal fossa, which does not adjust for anatomical variability, and may place the block site distal to the division of the sciatic nerve. An alternative intermuscular (between biceps femoris and semitendinosus muscles) approach identifies the popliteal-scaitic block site, adjusts for anatomical variation and potentially selects a block site above the division of the nerve (1). The purpose of this randomized prospective, single blinded study was to compare the latency and success of a complete sciatic nerve block using the classic Labat approach and the intermuscular approach to popliteal-sciatic nerve block.
Methods: After IRB approval and a written informed consent, ASA I-III patients undergoing foot/ankle surgery participated. Blocks were performed with the patient in the prone position, with the ankle of the surgical leg supported on a blanket roll to permit unrestricted foot movement. Patients were randomly (sealed envelop) assigned to the classic Labat approach (n=50), needle entry site 7-8 cm above the knee crease 1 cm lateral to midline of popliteal fossa, or the intermuscular approach, the site was determined by identifying the intermuscular groove between the biceps femoris laterally and semitendinosus and
semimembranosus medially (approximately12-14cm above the knee crease). A 100mm 22g insulated needle connected to a nerve stimulator was used for nerve location. The end point for local anesthetic injection was a brisk evoked motor response (EMR) – Peroneal (eversion or dorsiflexion), or tibial (plantar flexion) or a combined peroneal/tibial (inversion). Bupivacaine 0.625% with epinephrine 1:300,000 was injected incrementally, total volume 0.4 ml/kg (min. 25ml, max. 35ml). Assessments for the onset of sensory and motor block were performed every 2 mins for 10 mins, and then every 5 mins until 60 mins in the distributions of the tibial and common peroneal nerves. Complete block was defined as pinprick anesthesia and motor paralysis in both nerve distributions. The frequency of complete block and patient characteristics were compared using the Mann Whitney U-test and the 2 statistics. Kaplan-Meir curves and the log-rank test were constructed to
compare block latencies stratified by EMR between groups. A P=0.05 was required to reject the null hypothesis.
Results: The groups were similar in age, gender distribution, BMI, volume of local anesthetic, and EMR response distribution prior to injection. A complete block was achieved
in 70% using the Labat approach and 82% of patients using the intramuscular approach (P=0.18). An EMR of combined peroneal/tibial origin (inversion) resulted in a faster onset of
complete block compared to an EMR of peroneal or tibial alone, but there were no differences when block site was stratified by EMR (fig).
Conclusions: The intermuscular approach to popliteal fossa sciatic nerve block resulted in a similar frequency of complete block as the traditional Labat approach. This method has the advantage of using easily identifiable anatomical landmarks for selecting the block site.
References:
1.) Bogeat A, et al. Reg Anesth Pain Med 2004;29:290-6.

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