Subsartorial adductor canal vs femoral nerve block for analgesia after total knee replacement

Purpose Providing effective analgesia for total knee arthroplasty (TKA) patients remains challenging. Femoral nerve block (FNB) offers targeted pain control; however, its effect on motor function, related fall risk and impact on rehabilitation has been the source of controversy. Adductor canal block (ACB) potentially spares motor fibres of the femoral nerve, but the comparative effect of the two approaches has not yet been well defined due to considerable variability in pain perception. Our study compares both single-shot FNB and ACB, side to side, in the same patients undergoing bilateral TKA. Methods Sixty patients scheduled for bilateral TKA were randomised to receive ultrasound-guided FNB on one leg and ACB on the other, in addition to combined spinal epidural anaesthesia. The primary outcome was comparative postoperative pain in either extremity at six to eight, 24 and 48 hours postoperatively. Secondary comparative outcomes included motor strength (manually and via dynamometer), physical therapy milestones and patient satisfaction. Results While pain levels were lowest at six to eight hours postoperatively and increased thereafter (P < 0.001), no significant differences were seen between extremities at any time point with regard to pain in the quantitative comparison using visual analogue scale (VAS) scores (P = 0.4154), motor strength (P = 0.7548), physical therapy milestones or patient satisfaction. However, in the qualitative comparison, a significant proportion of patients reported the leg receiving ACB to be more painful than that receiving FNB at 24 h [50.9 % (n = 30) vs 25.42 % (n = 15), P = 0.0168)]. Conclusions Although we could not confirm a benefit in motor function between ACB and FNB, given the equivalent analgesic potency combined with its potentially lower overall impact if neuropraxia should occur, ACB may represent an attractive alternative to FNB.