title: Motor innervation of the trapezius muscle: Intraoperative motor conduction study during neck dissection.
abstract: OBJECTIVE
  To evaluate the motor input from the spinal accessory nerve (SAN) and the branches of the cervical plexus in an intraoperative motor nerve conduction study measuring motor action potentials by direct stimulation of the exposed nerve during neck dissection.
  
  
  METHODS
  The entire length of the SAN and the contributions from the upper cervical plexus were preserved. Compound muscle action potentials were measured for each part of the trapezius muscle on stimulation of the SAN, C2, C3, and C4 nerves.
  
  
  RESULTS
  With stimulation of the spinal nerve, evoked responses were obtained from all 24 patients in the descending, transverse, and ascending trapezius muscle. C2 contributions were noted in 2 out of 24 patients; however, no patient revealed responses in all three parts of the muscle. C3 contributions were seen in 11 out of 24 patients, supplying all three parts of the muscle in 8 patients, and C4 contributions were noted in 20 out of 24 patients, supplying all three parts of the muscle in 16 of them.
  
  
  CONCLUSIONS
  The SAN provided the most consistent motor input to the trapezius muscle. The C2, C3, and C4 nerves also provided motor input to the trapezius muscle; however, they were either inconsistently present or, when present, irregularly innervated the three parts of the trapezius muscle.
authors.affiliation: Department of Otorhinolaryngology - Head and Neck Surgery, Ilsong Memorial Institute of Head and Neck Cancer, Hallym University College of Medicine, Seoul, Korea.
authors.forename: Jin Hwan
authors.initials: JH
authors.lastname: Kim
authors.forename: Kyu Young
authors.initials: KY
authors.lastname: Choi
authors.forename: Kyu Ho
authors.initials: KH
authors.lastname: Lee
authors.forename: Dong Jin
authors.initials: DJ
authors.lastname: Lee
authors.forename: Bum Jung
authors.initials: BJ
authors.lastname: Park
authors.forename: Young-Soo
authors.initials: YS
authors.lastname: Rho
mesh_terms: D000055:Accessory Nerve / Q000502:physiology*; D000200:Action Potentials / Q000502:physiology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002572:Cervical Plexus / Q000502:physiology*; D004576:Electromyography; D005260:Female; D006258:Head and Neck Neoplasms / Q000601:surgery*; D006801:Humans; D007432:Intraoperative Period; D008207:Lymphatic Metastasis; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D037981:Neck Dissection; D009431:Neural Conduction / Q000502:physiology*; D064171:Superficial Back Muscles / Q000294:innervation*