An inferior shoulder dislocation is the least common form of shoulder dislocation. The condition is also called luxatio erecta because the arm appears to be permanently held upward, in fixed abduction. The patient will often present with their hand placed on the head or near it.
It is caused either of the following mechanisms:
- sudden forceful arm hyperabduction
- less commonly, direct loading force on fully abducted arm, with extended elbow and pronated forearm
The humeral head is displaced directly below and slightly medial to the glenoid fossa, with the arm often in marked abduction (luxatio erecta).
An inferior dislocation can mimic a subcategory of glenohumeral dislocation known as subglenoid anterior dislocation, where the humeral head rests directly inferior to the glenoid in the AP and lateral projections . It is distinguished from the latter by the humeral shaft's position parallel to the scapular spine.
MRI is performed post-reduction. Common findings include :
- rotator cuff tears
- injuries to the glenoid labrum
- injuries to both the anterior and posterior band of the inferior glenohumeral ligament (IGHL)
- bone bruises or impaction fractures (Hill-Sachs lesion) at the superolateral aspect of the humeral head
Inferior dislocations have a high complication rate, with secondary osseous, soft tissue. vascular, neurological, tendon, and ligament injuries.