Femoral Nerve Blockade versus Adductor Canal Nerve Blockade with Anterior Cruciate Ligament Reconstruction: A Prospective, Randomized Clinical Trial

OBJECTIVES: Post-operative pain control is critical to successful outcomes following outpatient anterior cruciate ligament (ACL) reconstruction. Femoral nerve blockade (FNB) has traditionally been employed to provide analgesia for ACLR since its inception in the early 1990’s. Recent studies, however, suggest a significant reduction in quadriceps muscle strength, and increased fall risk with the use of FNB. To mitigate the loss in muscle function and patient safety, surgeons and anesthesiologists have recently been exploring the potential benefits of a motor sparing adductor canal nerve blockade (ACB). To date, however, few comparative studies exist within an ACL reconstruction population to determine its clinical utility. Therefore, the purpose of this study was to compare acute pain control, quadriceps muscle activation and patient function between FNB and ACB following ACL reconstruction out to 4 weeks. METHODS: One-hundred and twenty-three patients (ACB, n = 63 and FNB, n= 60) undergoing ACL reconstruction by a single surgeon (WRL) were recruited to participate in this study. Patient demographics were similar for age (28.3 ±11.1 vs 26.7 ±10.0; P =.68), gender (61.9% male vs % male; P =.17), and BMI (26 ±6 vs 27 ±8; P =.79) for ACB and FNB groups, respectively. Pain control was measured within the first 24 hours of surgery using the numeric pain rating scale (NPRS) and opioid use in morphine units (mg). Quadriceps muscle activation was measured using surface electromyography (EMG) and recorded as the deficit between the involved and uninvolved limbs (µV). Quadriceps function was clinically assessed by the number of straight leg raises performed (without a lag), and the ability to meet our criteria for ambulation without an assistive device at 24 hrs, 2 wks, and 4 wks postoperatively. A mixed-model ANOVA (group x time) was used for all statistical comparisons with an a priori α =.05. RESULTS: There were no differences in NPRS score (2.4 ±1.7 vs 2.6 ±2.0; P =.52), and Morphine units (24.1 mg ±16.3 vs 22.8 mg ±15.6; P =.61) for ACB and FNB groups thru 24 hours post-surgery. Quadriceps muscle activation deficits were lower for the ACB group at each testing timeframe (Figure 1); 24 hours (196.2 µV ±21.0 vs 227.6 µV±23.7; P =.02), 2 weeks (87.3 µV ±19.5 vs 179.2 µV ±15.2; P <.01), and 4 weeks (56.4 µV ±18.3 vs 118.9 µV ±17.1; P =.02). The ability to meet criteria for ambulation without an assistive device was higher at 4 weeks for patients receiving ACB versus FNB (98.4% vs 90.0% ; P =.01). No statistical differences were observed for the number of straight leg raises performed at any timeframe (P >.05). CONCLUSION: The primary results of this study show that ACB provides similar pain control with improved quadriceps muscle activation compared to FNB acutely following ACL reconstruction. Additionally, the ability to ambulate without an assistive device appears to occur sooner for patients receiving ACB. No differences were observed in the number of straight leg raises performed up to 4 wks post-surgery. Surgeons should consider the potential benefits of ACB for post-operative analgesia when performing ACL reconstruction.