title: MR arthrography including abduction and external rotation images in the assessment of atraumatic multidirectional instability of the shoulder.
abstract: OBJECTIVE
  To evaluate diagnostic signs and measurements in the assessment of capsular redundancy in atraumatic multidirectional instability (MDI) of the shoulder on MR arthrography (MR-A) including abduction/external rotation (ABER) images.
  
  
  METHODS
  Twenty-one MR-A including ABER position of 20 patients with clinically diagnosed MDI and 17 patients without instability were assessed by three radiologists. On ABER images, presence of a layer of contrast between the humeral head (HH) and the anteroinferior glenohumeral ligament (AIGHL) (crescent sign) and a triangular-shaped space between the HH, AIGHL and glenoid (triangle sign) were evaluated; centring of the HH was measured. Anterosuperior herniation of the rotator interval (RI) capsule and glenoid version were determined on standard imaging planes.
  
  
  RESULTS
  The crescent sign had a sensitivity of 57 %/62 %/48 % (observers 1/2/3) and specificity of 100 %/100 %/94 % in the diagnosis of MDI. The triangle sign had a sensitivity of 48 %/57 %/48 % and specificity of 94 %/94 %/100 %. The combination of both signs had a sensitivity of 86 %/90 %/81 % and specificity of 94 %/94 %/94 %. A positive triangle sign was significantly associated with decentring of the HH. Measurements of RI herniation, RI width and glenoid were not significantly different between both groups.
  
  
  CONCLUSIONS
  Combined assessment of redundancy signs on ABER position MR-A allows for accurate differentiation between patients with atraumatic MDI and patients with clinically stable shoulders; measurements on standard imaging planes appear inappropriate.
  
  
  CONCLUSIONS
  MR arthrography has the possibility to accurately identify patients with atraumatic MDI. Imaging of the shoulder in abduction and external rotation provides additive information. Capsular enlargement of the shoulder can be diagnosed on MR arthrography.
authors.affiliation: Department of Radiology, Technische Universität München, Ismaninger Str.22, 81675, Munich, Germany, schaeffeler@me.com.
authors.forename: Christoph
authors.initials: C
authors.lastname: Schaeffeler
authors.forename: Simone
authors.initials: S
authors.lastname: Waldt
authors.forename: Jan S
authors.initials: JS
authors.lastname: Bauer
authors.forename: Chlodwig
authors.initials: C
authors.lastname: Kirchhoff
authors.forename: Bernhard
authors.initials: B
authors.lastname: Haller
authors.forename: Michael
authors.initials: M
authors.lastname: Schröder
authors.forename: Ernst J
authors.initials: EJ
authors.lastname: Rummeny
authors.forename: Andreas B
authors.initials: AB
authors.lastname: Imhoff
authors.forename: Klaus
authors.initials: K
authors.lastname: Woertler
mesh_terms: D000293:Adolescent; D000328:Adult; D002062:Bursitis / Q000473:pathology*; D002648:Child; D005260:Female; D006801:Humans; D006811:Humerus / Q000473:pathology; D017746:Joint Capsule / Q000473:pathology; D007593:Joint Instability / Q000473:pathology*; D008023:Ligaments, Articular / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D012399:Rotation; D012680:Sensitivity and Specificity; D012782:Shoulder; D012785:Shoulder Joint / Q000473:pathology*; D055815:Young Adult