title: Adductor canal block versus femoral nerve block and quadriceps strength: a randomized, double-blind, placebo-controlled, crossover study in healthy volunteers.
abstract: BACKGROUND
  The authors hypothesized that the adductor canal block (ACB), a predominant sensory blockade, reduces quadriceps strength compared with placebo (primary endpoint, area under the curve, 0.5-6 h), but less than the femoral nerve block (FNB; secondary endpoint). Other secondary endpoints were adductor strength and ability to ambulate.
  
  
  METHODS
  The authors enrolled healthy young men into this double blind, placebo-controlled, randomized, crossover study. On two separate study days, subjects received either ACB or FNB with ropivacaine, and placebo in the opposite limb. Strength was assessed as maximum voluntary isometric contraction for quadriceps and adductor muscles. In addition, subjects performed three standardized ambulation tests. Clinicaltrials.gov Identifier: NCT01449097.
  
  
  RESULTS
  Twelve subjects were randomized, 11 analyzed. Quadriceps strength (area under the curve, 0.5-6 h) was significantly reduced when comparing ACB with placebo (5.0 ± 1.0 vs. 5.9 ± 0.6, P = 0.02, CI: -1.5 to -0.2), FNB with placebo (P = 0.0004), and when comparing FNB with ACB (P = 0.002). The mean reduction from baseline was 8% with ACB and 49% with FNB. The only statistically significant difference in adductor strength was between placebo and FNB (P = 0.007). Performance in all mobilization tests was reduced after an FNB compared with an ACB (P < 0.05).
  
  
  CONCLUSIONS
  As compared with placebo ACB statistically significantly reduced quadriceps strength, but the reduction was only 8% from baseline. ACB preserved quadriceps strength and ability to ambulate better than FNB did. Future studies are needed to compare the analgesic effect of the ACB with the FNB in a clinical setting.
authors.affiliation: Department of Anaesthesia, Centre of Head and Orthopaedics, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark. pia.jaeger@rh.regionh.dk
authors.forename: Pia
authors.initials: P
authors.lastname: Jaeger
authors.forename: Zbigniew J K
authors.initials: ZJ
authors.lastname: Nielsen
authors.forename: Maria H
authors.initials: MH
authors.lastname: Henningsen
authors.forename: Karen Lisa
authors.initials: KL
authors.lastname: Hilsted
authors.forename: Ole
authors.initials: O
authors.lastname: Mathiesen
authors.forename: Jørgen B
authors.initials: JB
authors.lastname: Dahl
mesh_terms: D000293:Adolescent; D000328:Adult; D018592:Cross-Over Studies; D004311:Double-Blind Method; D023381:Endpoint Determination; D005267:Femoral Nerve; D006801:Humans; D007866:Leg / Q000502:physiology; D008297:Male; D053580:Muscle Strength / Q000187:drug effects*; D009407:Nerve Block / Q000379:methods*; D052097:Quadriceps Muscle / Q000187:drug effects*; D018401:Sample Size; D013848:Thigh; D016896:Treatment Outcome; D016138:Walking; D055815:Young Adult