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

Anterior Dislocation of the Humeral Head

Anterior Dislocation of the Humeral Head: Top image shows humeral head displaced from glenoid and lying inferior to the coracoid process (red arrow); the middle image demonstrates a defect along the posterolateral aspect of the head, which is the Hill-Sach's deformity (green arrow). The lower image is the scapular Y view (blue line outlines scapula). The head lies in a subcoracoid (i.e. anterior location). The white arrows point to the acromion.

    • 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

posterior shoulder dislocation

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.

  • 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

Luxatio Erecta (Inferior Dislocation).

Luxatio Erecta (Inferior Dislocation). The humeral head (white arrow) lies below (inferior) to the
glenoid (black arrow) and the arm is fixed in abduction.

  • Superior shoulder dislocation (<1%)

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