Preferable Concentration-Volume Combination of Ropivacaine for Femoral Nerve Block in Arthroscopic Meniscoplasty: A Prospective, Double-Blind, Randomized Clinical Trial

Purpose: This study aimed to determine the preferable combination of ropivacaine balancing analgesic efficacy with minimal motor impairment under fixed total dosage for ultrasound-guided femoral nerve block (FNB) in meniscoplasty patients. Patients and Methods: In this randomized double-blind trial, 200 patients scheduled for arthroscopic meniscus repair were allocated to four groups receiving ultrasound-guided FNB with equivalent 50 mg ropivacaine doses [ R0.17 : 0.17% (30 mL); R0.20 : 0.20% (25 mL); R0.25 : 0.25% (20 mL); R0.33 : 0.33% (15 mL)]. The primary outcome was area under curve (AUC) of visual analog scale (VAS) pain intensity scores on movement through 24 hours postoperatively. Results: Statistically significant intergroup differences were observed in the AUC of VAS pain intensity scores on movement through 24 and 48 hours postoperatively ( R0.33 < R0.20 < R0.17; R0.25 ≈ R0.20 < R0.17 ). The AUC of VAS scores at rest through 24 hours postoperatively showed: R0.33 < R0.25 < R0.20 < R0.17 ; and at 48 hours: R0.33 ≈ R0.25 < R0.20 < R0.17 . The AUC of sensory block scores through 24 and 48 hours postoperatively showed: R0.33 > R0.25 ≈ R0.20 > R0.17 . In terms of postoperative motor block scores, no significant difference was found between the R0.17 and R0.20 groups ( P = 0.2233), but both were significantly lower than the R0.25 and R0.33 groups ( P < 0.05). The AUC of quadriceps muscle strength scores through 24 hours postoperatively showed: R0.33 < R 0.25 < R 0.20 < R 0.17 ; and at 48 hours: R 0.33 < R 0.25 < R 0.20 ≈ R 0.17 . The number of patients requiring rescue analgesia was significantly higher in the R0.17 group than in the other three groups ( P = 0.0013). Conclusion: At a dose of 50 mg ropivacaine, 0.20% ropivacaine (25 mL) for FNB provided effective postoperative analgesia for patients undergoing arthroscopic meniscoplasty, while allowing for earlier recovery of muscle strength. Keywords: ultrasound guidance, femoral nerve block, ropivacaine, sensory block, motor block