Electromyographic Comparison of the Efficacy of Ultrasound-guided Suprainguinal and Infrainguinal Fascia Iliaca Compartment Block for Blockade of the Obturator Nerve in Total Knee Arthroplasty

Background and Objectives: The knee is innervated by the femoral, obturator, and sciatic nerves. An infrainguinal fascia iliaca compartment block (FICB) is often used as a technique for pain management after hip and knee arthroplasty. This approach blocks the femoral nerve, lateral femoral cutaneous nerve, and obturator nerve. Previous studies show suprainguinal FICB achieves improved postoperative analgesia compared with infrainguinal FICB after hip fracture. However, the analgesic effects of suprainguinal or infrainguinal FICB on the obturator nerve after total knee arthroplasty (TKA) remain to be established. This study compared the efficacy of suprainguinal versus infrainguinal FICB for the blockade of the obturator nerve using electromyography and quantification of total opioid consumption during the 24 hours after TKA. Methods: This prospective, randomized controlled clinical study enrolled 74 patients scheduled to undergo TKA. Patients were randomized 1:1 to receive suprainguinal FICB (group S) or infrainguinal FICB (group I) with 30 mL of 0.375% ropivacaine. The primary endpoint was the mean amplitude of the adductor longus compound muscle action potential (CMAP) at 0 (before the block), 10, 20, and 30 minutes after FICB. The secondary endpoint was total opioid consumption during the 24 hours after TKA. Results: Data from 62 patients were included in the analysis. The mean amplitude of the adductor longus CMAP was significantly lower in group S compared with group I (repeated-measures analysis of variance; F =4.73, P =0.034). At 24 hours after TKA, mean (SD) total opioid consumption was significantly lower in group S, compared with group I (131.5±76.8 vs. 201.5±85.1 μg) ( P =0.001). Conclusions: Suprainguinal FICB significantly increased the incidence of successful obturator nerve block and significantly decreased fentanyl consumption 24 hours after TKA compared with infrainguinal FICB.