Effects of continuous intravenous lidocaine infusion versus adductor canal block on postoperative pain and functional recovery after arthroscopic knee surgery: a non-inferiority randomized controlled trial

Arthroscopic knee surgery is increasingly performed in ambulatory settings, where effective analgesia and rapid recovery are essential. However, the incremental benefit of adductor canal block (ACB) over systemic analgesic strategies remains uncertain. This study aimed to evaluate whether continuous intravenous lidocaine is non-inferior to ACB for postoperative analgesia and recovery. In this prospective, randomized, observer-blinded non-inferiority trial, 76 patients undergoing ambulatory arthroscopic meniscal surgery under general anesthesia were assigned to intravenous lidocaine (1.5 mg/kg loading, 2 mg/kg/h infusion) or ultrasound-guided ACB (15 mL 0.2% ropivacaine). The primary outcome was the mean 24-hour postoperative resting pain score (Numerical Rating Scale, NRS, 0–10). Secondary outcomes included quadriceps strength, Quality of Recovery-15 (QoR-15) score, paresthesia, rescue analgesia, adverse events, and time to discharge. Analyses were performed on an intention-to-treat (ITT) basis. Mean 24-hour pain scores were comparable (0.82 ± 0.75 vs. 0.79 ± 0.78), with a difference of 0.03. The upper bound of the one-sided 97.5% confidence interval was 0.4, which was below the predefined non-inferiority margin (Δ = 1.0), confirming non-inferiority. Pain scores and rescue analgesia were similar. Quadriceps strength was higher with lidocaine at 1 h and 24 h ( P < 0.05). QoR-15 was slightly higher with ACB ( P = 0.05) but did not reach clinical significance. Paresthesia was less frequent with lidocaine (3% vs. 26%, P = 0.01). Time to discharge was shorter with lidocaine (4.98 ± 1.80 h vs. 6.34 ± 1.36 h, P = 0.007). Intravenous lidocaine provides non-inferior analgesia to ACB and is associated with better quadriceps function, fewer sensory disturbances, and earlier discharge after ambulatory arthroscopic meniscal surgery. Chinese Clinical Trial Registry (ChiCTR2500095362), registered on January 6, 2025.