Continuous femoral nerve block is not superior to continuous adductor canal block for postoperative pain following ACL reconstruction

1. Continuous femoral nerve block (CFNB) was not superior to continuous adductor canal block for the primary outcome of average postoperative pain over 48 hours following ACL reconstruction, despite CFNB showing lower pain immediately after surgery and a lower exploratory rate of high opioid consumption.

Evidence Rating Level: 1 (Excellent)

Study Rundown: This single-center, double-blind randomized controlled trial compared continuous femoral nerve block (CFNB) versus continuous adductor canal block (CACB) in 57 patients undergoing ACL reconstruction. The primary outcome of average pain scores at 24 and 48 hours showed no significant difference between groups (treatment effect −0.31 NRS points, p=0.58). CFNB was associated with significantly lower pain immediately after surgery (POD0), though this finding lacked correction for multiple comparisons. In an exploratory analysis, fewer CFNB patients required more than 50 morphine milligram equivalents over 48 hours compared with CACB patients (18% vs 45%, p=0.045), though the confidence interval for this difference crossed zero, and day-by-day analyses were not significant. No differences emerged in continuous passive motion use/compliance or Quality of Recovery-15 scores. The authors concluded CFNB was not superior to CACB on the primary endpoint, and the trade-off between quadriceps strength and fall risk remain unassessed and require further study.

Click to read the study in BMJ Regional Anesthesia & Pain Medicine

Relevant Reading: Pain Management After Outpatient Anterior Cruciate Ligament Reconstruction: A Systematic Review of Randomized Controlled Trials

In-Depth [Randomized Controlled Trial]: Anterior cruciate ligament (ACL) reconstruction is one of the most common orthopedic procedures in the United States, with approximately 200,000 performed annually, and postoperative pain remains a major barrier to recovery and early rehabilitation. Continuous femoral nerve blocks (CFNB) and continuous adductor canal blocks (CACB) are the two most widely used regional anesthesia techniques for this surgery. CFNB provides broader sensory coverage of the knee but causes quadriceps motor weakness, while CACB spares motor function by targeting the saphenous nerve but may provide less complete analgesic coverage. Although prior studies (mostly from total knee arthroplasty literature or retrospective ACL data) have compared these approaches, no randomized controlled trial had directly compared continuous catheter techniques specifically in ACL reconstruction prior to this study.

This was a single-center, double-blind, superiority randomized controlled trial conducted at Stanford between 2018 and 2023. Sixty adults undergoing ACL reconstruction were randomized 1:1 to CFNB or CACB. All patients received a 20 mL loading dose of 0.5% ropivacaine followed by a 0.2% ropivacaine infusion (5 mL/hour basal, 5 mL demand bolus, 30-minute lockout) via catheter after discharge. The primary outcome was average numeric rating scale (NRS) pain score at 24 and 48 hours, analyzed with a linear mixed-effects repeated-measures model. Secondary outcomes included cumulative morphine milligram equivalents (MME), continuous passive motion (CPM) usage and compliance, and Quality of Recovery-15 (QoR-15) scores. An exploratory post hoc analysis examined the proportion of patients exceeding 50 MME over the 48-hour period.

Fifty-seven patients completed the study (CFNB n=28, CACB n=29). On the primary outcome, there was no significant difference in average pain scores between groups; the estimated treatment effect for CFNB versus CACB was −0.31 NRS points (p=0.58, 95% CI −1.39 to 0.77), with no significant treatment-by-time interaction (p=0.97). In secondary analysis, current pain on postoperative day 0 (POD0) was significantly lower in the CFNB group (median 2.5 vs 4, p=0.02), though this finding should be interpreted cautiously given multiple comparisons without correction. No other pain domains (rest, motion, worst pain) differed significantly between groups at any time point. Total cumulative MME did not differ significantly between groups overall (p=0.06). However, in an exploratory analysis, fewer CFNB patients required more than 50 MME over the 48-hour postoperative period compared with CACB patients (5/28 vs 13/29; p=0.045, absolute risk difference 0.27, 95% CI −0.08 to 0.54), though this finding was not significant when each postoperative day was analyzed independently, and the confidence interval for the risk difference crossed zero. There were no significant differences between groups in CPM use, CPM compliance, or QoR-15 scores at either POD1 or POD2.

The authors concluded that CFNB was not superior to CACB for the primary pain outcome over 48 hours following ACL reconstruction. CFNB was associated with lower immediate (POD0) pain and, in exploratory analysis, a lower proportion of patients exceeding a 50 MME threshold, but these opioid-related findings are hypothesis-generating rather than definitive given the study’s modest sample size, lack of multiplicity correction, and an original power calculation based on an optimistic effect size. Importantly, the study did not assess quadriceps strength or fall risk, so the clinical trade-off between analgesic benefit and motor blockade remains unresolved and warrants further investigation in adequately powered trials, potentially in higher-risk populations such as opioid-tolerant patients.

Image: PD

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