title: Posterior interosseous nerve of the elbow: normal appearances simulating entrapment.
abstract: OBJECTIVE
  In our clinical practice, we have noted a caliber change of the posterior interosseous nerve (PIN) at the elbow as seen in the long axis on sonography simulating nerve entrapment. The objective of this study was to characterize the PIN using sonography in asymptomatic individuals.
  
  
  METHODS
  Our study retrospectively characterized the PIN in 50 elbows of 47 asymptomatic patients with sonography. Measurements of the PIN in a short-axis cross section using the circumferential trace technique and the anteroposterior (AP) dimension in the long axis were made proximal, at, and distal to the arcade of Frohse.
  
  
  RESULTS
  There was reduction of the AP dimension of the PIN distal to the arcade of Frohse when compared with the measurements at the arcade of Frohse and proximal to the arcade (P < .0001); however, there was no significant difference between the cross-sectional area of the PIN at all 3 levels (P = .59).
  
  
  CONCLUSIONS
  The PIN normally flattens as it enters into the supinator muscle without a notable change in the cross-sectional area. This appearance should not be misinterpreted as nerve entrapment when imaged in the long axis.
authors.affiliation: Department of Radiology, University of Michigan Hospital, Ann Arbor, MI 48109 USA. bingch@med.umich.edu
authors.forename: Qian
authors.initials: Q
authors.lastname: Dong
authors.forename: David A
authors.initials: DA
authors.lastname: Jamadar
authors.forename: Brian L
authors.initials: BL
authors.lastname: Robertson
authors.forename: Jon A
authors.initials: JA
authors.lastname: Jacobson
authors.forename: Elaine M
authors.initials: EM
authors.lastname: Caoili
authors.forename: Thomas
authors.initials: T
authors.lastname: Gest
authors.forename: Gandikota
authors.initials: G
authors.lastname: Girish
mesh_terms: D000328:Adult; D000368:Aged; D003937:Diagnosis, Differential; D004550:Elbow / Q000000981:diagnostic imaging*; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009408:Nerve Compression Syndromes / Q000000981:diagnostic imaging*; D010525:Peripheral Nerves / Q000000981:diagnostic imaging*; D014463:Ultrasonography / Q000379:methods*; D055815:Young Adult