Proximal Versus Distal Continuous Adductor Canal Blocks: Does Varying Perineural Catheter Location Influence Analgesia? A Randomized, Subject-Masked, Controlled Clinical Trial

BACKGROUND: A continuous adductor canal block provides analgesia after surgical procedures of the knee. Recent neuroanatomic descriptions of the thigh and knee led us to speculate that local anesthetic deposited in the distal thigh close to the adductor hiatus would provide superior analgesia compared to a more proximal catheter location. We therefore tested the hypothesis that during a continuous adductor canal nerve block, postoperative analgesia would be improved by placing the perineural catheter tip 2–3 cm cephalad to where the femoral artery descends posteriorly to the adductor hiatus (distal location) compared to a more proximal location at the midpoint between the anterior superior iliac spine and the superior border of the patella (proximal location). METHODS: Preoperatively, subjects undergoing total knee arthroplasty received an ultrasound-guided perineural catheter inserted either in the proximal or distal location within the adductor canal in a randomized, subject-masked fashion. Subjects received a single injection of lidocaine 2% via the catheter preoperatively, followed by an infusion of ropivacaine 0.2% (8 mL/h basal, 4 mL bolus, 30 minutes lockout) for the study duration. After joint closure, the surgeon infiltrated the entire joint using 30 mL of ropivacaine (0.5%), ketorolac (30 mg), epinephrine (5 μg/mL), and tranexamic acid (2 g). The primary end point was the median level of pain as measured on a numeric rating scale (NRS) during the time period of 8:00 AM to 12:00 PM the day after surgery. RESULTS: For the primary end point, the NRS of subjects with a catheter inserted at the proximal location (n = 24) was a median (10th, 25th–75th, 90th quartiles) of 0.5 (0.0, 0.0–3.2, 5.0) vs 3.0 (0.0, 2.0–5.4, 7.8) for subjects with a catheter inserted in the distal location (n = 26; P = .011). Median and maximum NRSs were lower in the proximal group at all other time points, but these differences did not reach statistical significance. There were no clinically relevant or statistically significant differences between the treatment groups for any other secondary end point, including opioid consumption and ambulation distance. CONCLUSIONS: For continuous adductor canal blocks accompanied by intraoperative periarticular local anesthetic infiltration, analgesia the day after knee arthroplasty is improved with a catheter inserted at the level of the midpoint between the anterior superior iliac spine and the superior border of the patella compared with a more distal insertion closer to the adductor hiatus. Accepted for publication March 27, 2018. Funding: This work was supported by the Department of Anesthesiology, University of California San Diego (San Diego, CA). The authors declare no conflicts of interest. The contents of this article are solely the responsibility of the authors and do not necessarily represent the official views of the funding entity. Institutional review board: University California San Diego Human Research Protections Program at (858) 657–5100, 9500 Gilman Dr, La Jolla, CA 92093-0052. E-mail: tnelson@ucsd.edu. This report describes human research and a prospective randomized clinical trial. The authors state that the report includes every item in the Consolidated Standards of Reporting Trials (CONSORT) checklist for a prospective randomized clinical trial. This study was conducted with written informed consent from the study subjects. The study was registered before patient enrollment. This was not an observational clinical study. Registry URL: clinicaltrials.gov NCT02523235. Reprints will not be available from the authors. Address correspondence to Brian M. Ilfeld, MD, MS , Department of Anesthesiology, University California San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0898. Address e-mail to bilfeld@ucsd.edu. © 2018 International Anesthesia Research Society

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