title: Dynamic radiologic evaluation of horizontal instability in acute acromioclavicular joint dislocations.
abstract: BACKGROUND
  Biplane radiologic evaluation is indispensable for the correct diagnosis of acute acromioclavicular (AC) joint injuries. Thus far, no functional radiographic techniques have been quantified to evaluate horizontal instability in acute AC joint dislocations.
  
  
  OBJECTIVE
  Supine dynamic axillary lateral shoulder views detect horizontal instability of the distal clavicle in patients with acute AC joint dislocations.
  
  
  METHODS
  Cohort study (Diagnosis); Level of evidence, 2.
  
  
  METHODS
  Twenty-five consecutive patients with a mean age of 39 +/- 14 years with acute AC joint injury underwent biplane radiologic evaluation, including a conventional Zanca view and an axillary lateral view in a sitting position. In addition, supine axillary lateral views with the arm in 90 degrees of abduction and 60 degrees of flexion and extension were taken to evaluate the horizontal dynamics of the distal clavicle. The gleno-acromio-clavicular angle (GACA) was introduced and used to quantify the horizontal clavicular dynamics in terms of angle differences. The unaffected shoulders served as the control group.
  
  
  RESULTS
  Superior dislocation of the lateral clavicle in the Zanca view was classified as Rockwood type II in 7 patients, type III in 15, and type V in 3. The axillary lateral view in a sitting position showed posterior dislocation of the distal clavicle in 8 patients (Rockwood type IV injury). Dynamic radiologic evaluation revealed an average GACA difference between the neutral and anterior position of the arm of 7.1 degrees +/- 5.5 degrees for the unaffected shoulder. In the injured AC joints, 11 patients showed no radiologic evidence of horizontal instability (group A) with a GACA difference of 7.1 degrees +/- 4.8 degrees . Increased anteroposterior translation was evident in 14 patients (group B) with a GACA difference of 30.3 degrees +/- 14.3 degrees (P < .001).
  
  
  CONCLUSIONS
  Functional axillary radiologic evaluation seems to represent a simple imaging tool to reveal dynamic horizontal instability.
  
  
  CONCLUSIONS
  Horizontal instability of the distal clavicle in acute AC joint injuries represents an indication for surgical treatment. Dynamic axillary radiologic evaluation may detect previously missed unstable injuries. This evaluation might be relevant when deciding on surgical AC joint stabilization.
authors.affiliation: Department of Traumatology and Sports Injuries, Paracelsus Medical University Salzburg, Muellner Hauptstrasse 48, Salzburg, Austria. m.tauber@salk.at
authors.forename: Mark
authors.initials: M
authors.lastname: Tauber
authors.forename: Heiko
authors.initials: H
authors.lastname: Koller
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Hitzl
authors.forename: Herbert
authors.initials: H
authors.lastname: Resch
mesh_terms: D000173:Acromioclavicular Joint / Q000293:injuries*; D000328:Adult; D015331:Cohort Studies; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging*; D008875:Middle Aged; D011859:Radiography; D016059:Range of Motion, Articular / Q000502:physiology; D012783:Shoulder Dislocation / Q000175:diagnosis* / Q000000981:diagnostic imaging