Comparison of two different volumes of 0.5%, ropivacaine used in ultrasound-guided adductor canal block after knee arthroplasty: A randomized, blinded, controlled noninferiority trial

Background and Aims: The aim of this study was to establish noninferiority of 10 mL of 0.5% ropivacaine as compared to 20 mL of 0.5% ropivacaine; for choosing right dose in adductor canal block (ACB) after knee arthroplasty (KA), this trial was conducted. Material and Methods: Forty patients undergoing bilateral KA with postoperative ultrasound-aided ACB were randomized: Group A patients received 20 mL 0.5% ropivacaine in the right limb and 10 mL 0.5% ropivacaine in the left limb. Group B patients received 10 mL of 0.5% ropivacaine in the right limb and 20 mL of 0.5% ropivacaine in the left limb. Catheter is positioned for intermittent boluses every 12-h up to 48 h. Results: In the final analysis (excluding six patients) based on split-body design between Group I (comprising 34 limbs which received 20 mL of 0.5% ropivacaine) and Group II (comprising 34 limbs which received 10 mL of 0.5% ropivacaine), baseline demographic data were collected. Length of the limb from anterior superior iliac spine (ASIS) to the base of the patella was comparable between two groups: Group I (in cm; 149 ± 1.63) versus Group II (in cm; 149.5 ± 1.51) ( P = 0.49, 95% CI of – 1.98 to 0.98). Primary outcomes, that is, quadriceps muscle strength, show a significant difference ( P < 0.025) at various timeline. Secondary outcome pain scores and degree of knee flexion at various time intervals showed no significant difference. There was zero incidence of fall of the patient and no significant complication due to catheter was reported leading to discontinuation of catheter use in both groups. Conclusion: 10 mL of 0.5% ropivacaine is noninferior to 20 mL of 0.5% ropivacaine in providing postoperative analgesia with preserved quadriceps muscle strength.