Clinical evaluation of obturator nerve involvement following a supra-inguinal fascia iliaca compartment block: A randomized, double-blind trial.

BACKGROUND Clinical evidence on obturator nerve involvement after supra-inguinal fascia iliaca compartment block (SFICB) is limited. This study aimed to investigate whether a 40-mL SFICB reliably anesthetizes the obturator nerve and whether the addition of a selective obturator nerve block (ONB) improves postoperative analgesia in patients undergoing total knee arthroplasty.

METHODS In this randomized, double-blind, active-controlled trial, 84 patients who underwent total knee arthroplasty were randomized to receive SFICB (40 mL of 0.5% ropivacaine) plus either active (10 mL of 0.5% ropivacaine) or placebo (10 mL of normal saline) ONBs. Spinal anesthesia and postoperative analgesia were standardized. Two primary outcomes were (1) the success rate of ONB, measured 45 min after block completion, and (2) equivalent intravenous morphine consumption during the first 24 h postoperatively, tested following a predefined fixed-sequence procedure. Secondary outcomes included post-block sensorimotor function, pain scores, rescue analgesic use, patient satisfaction, sleep quality, recovery quality, and adverse effects within 48 h postoperatively.

RESULTS The success rate of ONB was significantly higher in the ONB group than in the placebo group (97.6% vs 2.4%; risk difference, 95.2%; 95% confidence interval, 81.2%-98.0%; P < 0.001). Equivalent intravenous morphine consumption during the first 24 h postoperatively did not differ significantly between the ONB and placebo groups (6.8 [2.5, 11.5] vs 7.8 [4.6, 17.5] mg; median difference, -2.5; 95% confidence interval, -5.0 to 0.5; P = 0.156). No differences were observed in the secondary outcomes, except for a greater reduction in adductor strength in the ONB group.

CONCLUSIONS An SFICB with 40 mL of 0.5% ropivacaine rarely anesthetized the obturator nerve. The addition of a selective ONB did not improve postoperative analgesia or recovery quality within 48 h after total knee arthroplasty. Further studies are needed to define the minimum effective SFICB volume that reliably involves the femoral and lateral femoral cutaneous nerves.

CLINICAL TRIAL REGISTRATION ChiCTR2300073558.