title: Sonography of the normal greater occipital nerve and obliquus capitis inferior muscle.
abstract: BACKGROUND
  To use sonography to measure the cross-sectional area (CSA) of the greater occipital nerve (GON) and the adjacent obliquus capitis inferior muscle (OCI) in normal subjects.
  
  
  METHODS
  Data from 30 asymptomatic subjects between the ages of 22 and 35 were collected. CSA and circumference of the GON and CSA of OCI were measured using sonography. Interexaminer reliability analysis was performed using the intraclass correlation coefficient.
  
  
  RESULTS
  The CSA of the GON and OCI were 2 mm2 +/- 1 mm2 and 1.86 cm2 +/- 0.51 cm2, respectively. The average circumference of the GON was 4.8 mm +/- 1.3 mm. The interexaminer reliability of the measurements was excellent with intraclass correlation coefficient coefficients of 0.91, 0.84, and 0.73 for the GON CSA, GON circumference, and OCI CSA, respectively.
  
  
  CONCLUSIONS
  We report the normal values of the CSA of the GON and OCI. Knowledge of these normal values may facilitate the diagnosis of GON entrapment and provide outcome measures in therapeutic interventions.
authors.affiliation: Department of Radiology, Logan College of Chiropractic, 1851 Schoettler Road, Box 1065, Chesterfield, MO 63006-1065, USA.
authors.forename: John Chin Suk
authors.initials: JC
authors.lastname: Cho
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Haun
authors.forename: Norman W
authors.initials: NW
authors.lastname: Kettner
authors.forename: Frank
authors.initials: F
authors.lastname: Scali
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Clark
mesh_terms: D000328:Adult; D001837:Body Weights and Measures / Q000379:methods; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008297:Male; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging*; D009334:Neck Muscles / Q000000981:diagnostic imaging* / Q000294:innervation*; D015588:Observer Variation; D010525:Peripheral Nerves / Q000000981:diagnostic imaging*; D015203:Reproducibility of Results; D014463:Ultrasonography; D055815:Young Adult