title: ECU tendon "dislocation" in asymptomatic volunteers.
abstract: OBJECTIVE
  Assess extensor carpi ulnaris (ECU) tendon position in the ulnar groove, determine the frequency of tendon "dislocation" with the forearm prone, neutral, and supine, and determine if an association exists between ulnar groove morphology and tendon position in asymptomatic volunteers.
  
  
  METHODS
  Axial proton density-weighted MR was performed through the distal radioulnar joint with the forearm prone, neutral, and supine in 38 asymptomatic wrists. The percentage of the tendon located beyond the ulnar-most border of the ulnar groove was recorded. Ulnar groove depth and length was measured and ECU tendon signal was assessed.
  
  
  RESULTS
  15.8 % of tendons remained within the groove in all forearm positions. In 76.3 %, the tendon translated medially from prone to supine. The tendon "dislocated" in 0, 10.5, and 39.5 % with the forearm prone, neutral and supine, respectively. In 7.9 % prone, 5.3 % neutral, and 10.5 % supine exams, the tendon was 51-99 % beyond the ulnar border of the ulnar groove. Mean ulnar groove depth and length were 1.6 and 7.7 mm, respectively, with an overall trend towards greater degrees of tendon translation in shorter, shallower ulnar grooves.
  
  
  CONCLUSIONS
  The ECU tendon shifts in a medial direction when the forearm is supine; however, tendon "dislocation" has not been previously documented in asymptomatic volunteers. The ECU tendon medially translated or frankly dislocated from the ulnar groove in the majority of our asymptomatic volunteers, particularly when the forearm is supine. Overall greater degrees of tendon translation were observed in shorter and shallower ulnar grooves.
authors.affiliation: Hospital for Joint Diseases, Department of Radiology, New York University Langone Medical Center, 301 East 17th Street, 6th floor Room 600, New York, NY, 10003, USA. petchc01@nyumc.org.
authors.forename: Catherine N
authors.initials: CN
authors.lastname: Petchprapa
authors.affiliation: Zwanger-Pesiri Radiology Group, 150 East Sunrise Highway, Lindenhurst, NY, 11757, USA.
authors.forename: Seema
authors.initials: S
authors.lastname: Meraj
authors.affiliation: New York University Langone Medical Center, Department of Radiology, New York University School of Medicine, 660 1st Avenue, New York, NY, 10016, USA.
authors.forename: Nidhi
authors.initials: N
authors.lastname: Jain
mesh_terms: D000328:Adult; D058070:Asymptomatic Diseases; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013708:Tendon Injuries / Q000000981:diagnostic imaging*; D014457:Ulna / Q000000981:diagnostic imaging* / Q000293:injuries*; D014954:Wrist Injuries / Q000000981:diagnostic imaging*
keywords: ECU; Instability; MRI