A randomised controlled trial comparing adductor canal block and femoral nerve block for knee arthroplasty

INTRODUCTION Adductor canal block (ACB) is hypothesised to provide superior analgesia to femoral nerve block (FNB) for total knee arthroplasty (TKA) while preserving quadriceps strength. METHODS 30 patients undergoing TKA were randomised to receive either ACB or FNB. Baseline tests of quadriceps strength were performed. Ultrasound-guided blocks with 30 mL of 0.5% ropivacaine were administered before induction of general anaesthesia. Patient-controlled analgesia (morphine) was prescribed for postoperative analgesia. The primary outcome of this prospective, double-blinded, randomised controlled trial was morphine consumption (mean +/- standard deviation) in the first 24 hours. Secondary outcomes were pain scores using a numeric rating scale (median and interquartile range [IQR]), quadriceps strength (% of baseline) and functional outcomes at 24 hours and 48 hours postoperatively. RESULTS There was no statistically significant difference in morphine consumption at 24 hours between the ACB and FNB groups (21 +/- 11 mg vs. 20 +/- 12 mg; p = 0.85). No statistically significant differences were observed between the ACB and FNB groups in pain scores at 24 hours (at rest: 0 [IQR 0-2] vs. 0 [IQR 0-2]; on movement: 5 [IQR 4-8] vs. 5 [IQR 3-8]) and quadriceps strength (24 hours: 28.8% +/- 26.1% vs. 26.8% +/- 19.6% of baseline; 48 hours: 31.5 +/- 23.1% vs. 33.7% +/- 20.1% of baseline). There were also no statistically significant differences in functional outcomes and length of stay. CONCLUSION We found no statistically significant differences in analgesic effects, quadriceps strength or functional recovery postoperatively between ACB and FNB.