Learning Radiology xray montage
 
 
 
 
 

Dislocations of the Shoulder
Posterior Shoulder Dislocation


 

  • Types of dislocations about the shoulder

    • Glenohumeral dislocation (the most common by far)
    • Acromioclavicular dislocation (12%)
    • Sternoclavicular dislocation (uncommon)

  • Types of glenohumeral dislocations

    • Anterior or subcoracoid shoulder dislocation (96%)
      • Mechanism
        • External rotation and abduction
        • 40% recurrent
      • Age
        • Younger individuals
      • May be associated with:
        • Fracture of greater tuberosity (15%)
        • Bankart lesion
          • Fracture of anterior glenoid rim
        • Hill-Sachs defect (50%)
          • Impaction fracture of posterolateral surface of humeral head due to impaction of humeral head against anterior rim of glenoid during dislocation

    • Posterior shoulder dislocation (2-4%)

      • Causes
        • Traumatic
          • Convulsive disorders or electroshock therapy
        • Nontraumatic
          • Congenital or developmental
          • May be done voluntarily, especially in children
        • Usually due to axial loading of an adducted and internally rotated arm
      • In >50% unrecognized initially and subsequently misdiagnosed as frozen shoulder
        • May be difficult to see on AP radiograph
        • Typically, a scapular Y view or transthoracic lateral of the humeral head demonstrate a posterior dislocation better
      • Imaging signs of posterior dislocation
        • Rim sign (66%) = distance between medial border of humeral head and anterior glenoid rim >6 mm
        • Humeral head is fixed in internal rotation no matter how forearm is turned – “lightbulb sign
        • May be associated with:
          • Trough sign (75%) = "reverse Hill-Sachs" = compression fracture of anteromedial humeral head
          • Fracture of posterior glenoid rim
          • Avulsion fracture of lesser tuberosity
            • Isolated  fractures of the lesser tuberosity should raise suspicion of an associated posterior dislocation
  • Inferior shoulder dislocation (1-2%)

    • Luxatio erecta
      • Extremity held over head in fixed position with elbow flexed
    • Mechanism
      • Severe hyperabduction of arm resulting in impingement of humeral head against acromion
      • Humeral articular surface faces inferiorly
    • Complications
      • Rotator cuff tear
      • Fracture of acromion with or without inferior glenoid fossa and with or without fracture of the greater tuberosity
      • Neurovascular injury

  • Superior shoulder dislocation (<1%)

    • Humeral head driven upward through rotator cuff
    • May be associated with fracture of humerus, clavicle or acromion

 

 

 

 
Posterior Dislocation of the Shoulder.
Image on left demonstrates a "trough fracture" or "reverse Hill-Sachs fracture"of the antero-medial aspect of the humeral head (red arrow) as well as widening of the glenohumeral joint space (black arrow). The scapular Y view on the right shows that the humeral head (white arrow) no longer resides in the glenoid (G) but posterior to the acromion (A), The coracoid process is marked C.