Question
51 year-old fell on outstretched arm.X ray shows the following features.What can be the diagnosis?
A. Anterior Dislocation
B. Posterior Dislocation
C. Superior Dislocation
D. Inferior Dislocation
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Correct Answer » D Explanation |
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Ans:D. Inferior Dislocation.
Image shows:Luxatio Erecta (Inferior Dislocation). The humeral head (white arrow) lies below (inferior) to the glenoid (black arrow) and the arm is fixed in abduction.
Types of dislocations about the shoulder
- Glenohumeral dislocation (the most common by far)
- Acromioclavicular dislocation (12%)
- Sternoclavicular dislocation (uncommon)
Types of glenohumeral dislocations
Inferior shoulder dislocation (1-2%)
Luxatio erecta ─ uncommon form of shoulder dislocation
- 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
Anterior or subcoracoid shoulder dislocation (most common) (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 (2nd most common) (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
- 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
Superior shoulder dislocation (least common) (<1%)
- Humeral head driven upward through rotator cuff
- May be associated with fracture of humerus, clavicle or acromion