Diagnosis: Inferior dislocation of the shoulder
The right shoulder x-ray (FIGURE 2) revealed luxatio erecta—an inferior dislocation of the shoulder. The humeral head was displaced inferiorly with respect to the glenoid fossa and there was an associated greater tuberosity fracture. The chest x-ray demonstrated mild pulmonary contusions.
FIGURE 2
Right shoulder radiograph reveals luxatio erecta with greater tuberosity fracture
An uncommon dislocation
Inferior shoulder dislocation or luxatio erecta is the least common type of glenohumeral dislocation, comprising only about 0.5% of all shoulder dislocations.1 The 2 other types of shoulder dislocations—anterior and posterior—account for 95% to 97% and 2% to 4% of dislocations, respectively.2
Injury occurs in one of 2 ways, either by a direct or indirect mechanism. A direct dislocation occurs when there is axial loading on an arm that is fully abducted at the shoulder.3 The indirect mechanism, which is more common, is caused by a hyperabduction stress that directs the humeral neck superiorly against the acromion process, forcing the humeral head out of the glenoid fossa inferiorly.2 The indirect mechanism usually occurs when a patient falls and reacts by grasping an object above his or her head, resulting in hyperabduction.
Sometimes, there is no trauma. True inferior dislocations have also been reported in patients with stroke, septic arthritis, and other neuromuscular diseases.4