Femoral nerve block (FNB) was associated with the perception of less severe pain after total knee arthroplasty, but adductor canal block (ACB) was associated with earlier mobility rehabilitation, according to a study published in Medicine.

Studies comparing ACB with FNB have been inconclusive regarding opioid-induced analgesia. This randomized, controlled trial (ClinicalTrials.gov: NCT03143738) was designed to compare total consumption of intravenous morphine administered via patient-controlled analgesia (PCA) for FNB vs ACB during post-total knee arthroplasty day 1. Conducted between June 2017 and July 2018, the study included 85 participants who were randomly assigned to either FNB or ACB. After surgery, both groups received intravenous morphine through a PCA pump with a lockout period of 10 minutes.

Secondary end points included postoperative pain evaluation via visual analog scale, quadriceps muscle strength, degree of knee extension, and ability to sit, stand, and walk; secondary end points were assessed 8, 24, and 48 hours after surgery as well as just before discharge from the orthopedic ward.

The FNB group had significantly fewer morphine uses compared with the ACB group (14, range 12-15 vs 20, range 18-22; P =.0001), and the FNB participants perceived significantly less severe pain at postoperative hours 8 (23, range 20-27 vs 40, range 37-43; P =.00003) and 24 (30, range 27-32 vs 38, 36-41; P =.0001).

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However, the ACB group showed significantly superior outcomes for most of the mobility parameters, including 8th- (P =.03) and 24th-hour (P =.006) muscle strength, 8th-hour degree of knee extension (P =.001), 8th-hour sitting (P =.007), 24th-hour standing upright (P =.0001), and 24th- and 48th-hour walking. After 24 hours, the sum of ranks for ACB was 2059 compared with 1596 for FNB (U=693, P =.001); after 48 hours, the sum of ranks for ACB was 2253 compared with 1402 for FNB (U=500, P =.001).

Study limitations included potential issues with strength and ability measurements, only including pain measurements at rest, and a failure to investigate differences in hospitalization lengths of stay. However, study investigators concluded, “in the current study FNB was superior to ACB with regard to intravenous morphine consumption after [total knee arthroplasty].

This observation was consistent with pain intensity measured via a VAS during the first postoperative day. However, quadriceps muscle strength, degree of knee extension, and ability to sit, stand upright, and walk were better in the ACB group. We believe that additional—particularly high-volume—studies are needed to facilitate a better understanding of the roles of ACB and FNB after [total knee arthroplasty].”

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Reference

Borys M, Domagała M, Wencław K, Jarczyńska-Domagała J, Czuczwar M. Continuous femoral nerve block is more effective than continuous adductor canal block for treating pain after total knee arthroplasty: A randomized, double-blind, controlled trial [published online September 3, 2019]. Medicine (Baltimore). doi: 10.1097/MD.0000000000017358