title: Double innervation of the brachialis muscle: anatomic-physiological study.
abstract: BACKGROUND
  Double innervation of the brachialis muscle has been previously reported in anatomical studies. This study aims to investigate the frequency and clinical significance of double innervation of brachialis by anatomical and electromyographic techniques.
  
  
  METHODS
  (1) The existence, origin and pattern of distribution of a branch from the radial nerve to brachialis were dissected on 20 cadaveric arms. (2) Nerve conduction studies (NCS) of 100 patients were performed. The radial nerve was stimulated, registering muscle potentials (MP) in the brachialis muscle. Subsequently, another MP was obtained by Erb's stimulation, corresponding to the whole brachialis innervation. The relative percentage of innervation from the radial nerve was calculated. (3) Two patients with lesions of the lateral cord of the brachial plexus and preserved elbow flexion were submitted to NCS.
  
  
  RESULTS
  Double innervation was found in 65 % of the anatomical preparations, following different patterns of distribution. In the NCS, 90% of the patients showed MP in the brachialis muscle after stimulating the radial nerve. The mean percentage of relative innervation was 11 %. Two patients with lesions of the lateral cord showed an important contribution from the radial nerve.
  
  
  CONCLUSIONS
  Variations in the relative percentage of innervation from the radial nerve could be due to the different sizes and shapes of this branch. The functional significance of this branch can become crucial if the main innervation to the brachialis muscle fails. When planning surgical antero-external approach to the humerus, it should be kept in mind and preserved.
authors.affiliation: III Normal Anatomy Department, School of Medicine, University of Buenos Aires, Paraguay 2155, 1211, Buenos Aires, Argentina. mbendersky@fmed.uba.ar
authors.forename: M
authors.initials: M
authors.lastname: Bendersky
authors.forename: H F
authors.initials: HF
authors.lastname: Bianchi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001132:Arm / Q000033:anatomy & histology / Q000294:innervation* / Q000502:physiology*; D001917:Brachial Plexus; D002102:Cadaver; D004576:Electromyography / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000294:innervation* / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology; D011826:Radial Nerve / Q000033:anatomy & histology / Q000502:physiology*