title: Is the musculocutaneous nerve really in the coracobrachialis muscle when performing an axillary block? An ultrasound study.
abstract: BACKGROUND
  In reference textbooks describing axillary block, the ulnar, radial, and median nerves are located in a common sheath surrounding the axillary artery. In contrast, the musculocutaneous nerve is described as lying outside this sheath in the coracobrachialis muscle. In a recent case report of ultrasound-guided axillary block, the musculocutaneous nerve was joined to the median nerve outside this muscle. Our study evaluated the prevalence of atypical musculocutaneous nerve localizations during axillary block.
  
  
  METHODS
  All patients undergoing ultrasound-guided axillary block were included from December 2006 to December 2008. Before needle insertion, musculocutaneous, median, ulnar, and radial nerves were localized using ultrasound. Nerve stimulation confirmed atypical nerve localization. After injection of local anesthetics, musculocutaneous and median nerve anatomical relationships were observed.
  
  
  RESULTS
  The musculocutaneous nerve was outside the coracobrachialis muscle in 83 of the 387 analyzed blocks (22%). It was near the axillary artery in 22 cases (6%). The musculocutaneous and median nerves appeared as a common neural structure in 61 cases (16%). After local anesthetic injection, a common trunk persisted in 16 of 61 cases (26%), musculocutaneous and median nerves separated in 37 cases (61%), and 2 roots of the median nerve appeared (with or without a separated musculocutaneous nerve) in 6 cases (10%). Two cases (3%) remained undefined. Ulnar nerve location of the 83 patients with atypical musculocutaneous nerve position differed from the ones with a classical musculocutaneous nerve localization.
  
  
  CONCLUSIONS
  During axillary block, the musculocutaneous nerve is outside the coracobrachialis muscle in 1 of 5 patients. This atypical location should be considered during performance of axillary blockade to avoid repeated IM puncture.
authors.affiliation: Groupement d'Anesthésie Réanimation, Hôpital Trousseau, Chambray lès Tours, CHRU Tours, F-37044 Tours cedex 9, France. f.remerand@chu-tours.f
authors.forename: Francis
authors.initials: F
authors.lastname: Remerand
authors.forename: Jacky
authors.initials: J
authors.lastname: Laulan
authors.forename: Claude
authors.initials: C
authors.lastname: Couvret
authors.forename: Michel
authors.initials: M
authors.lastname: Palud
authors.forename: Annick
authors.initials: A
authors.lastname: Baud
authors.forename: Stephane
authors.initials: S
authors.lastname: Velut
authors.forename: Marc
authors.initials: M
authors.lastname: Laffon
authors.forename: Jacques
authors.initials: J
authors.lastname: Fusciardi
mesh_terms: D000328:Adult; D000368:Aged; D000758:Anesthesia; D000779:Anesthetics, Local / Q000008:administration & dosage; D000886:Anthropometry; D001365:Axilla / Q000000981:diagnostic imaging*; D001366:Axillary Artery / Q000000981:diagnostic imaging; D002349:Carpal Tunnel Syndrome / Q000601:surgery; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000000981:diagnostic imaging; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000294:innervation*; D009138:Musculocutaneous Nerve / Q000002:abnormalities / Q000000981:diagnostic imaging*; D009407:Nerve Block / Q000379:methods*; D011826:Radial Nerve / Q000000981:diagnostic imaging; D014459:Ulnar Nerve / Q000000981:diagnostic imaging; D014463:Ultrasonography
chemical_list: D000779:Anesthetics, Local