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ANSWER

From the question on page 173.

Diagnosis

Posterior shoulder dislocation.

Imaging findings

Anteroposterior right shoulder

Several findings compatible with a posterior shoulder dislocation are present (fig 1). The humeral head is fixed in internal rotation, producing a “light-bulb” appearance and there is increased distance between the anterior glenoid rim and the medial aspect of the humeral head. The posterior humeral head is impacted onto the posterior rim of the glenoid (ellipse). A tiny fracture fragment is also seen overlying the axillary recess (arrow).

Figure 1

Anteroposterior radiograph of the right shoulder, with abnormal overlap of the posterior humeral head and posterior glenoid rim (black ellipse) and a loose fracture fragment (arrow).

Transscapular view

This view shows posterior dislocation of the humeral head relative to the glenoid. The humeral head should overlap the glenoid fossa (ellipse) on this view (fig 2).

Figure 2

Transscapular radiograph of the right shoulde, showing glenoid rim (ellipse) with the humeral head positioned posteriorly.

Axillary view

The humeral head is seen impacted onto the posterior rim of the glenoid with an impaction fracture of the anteromedial humeral head (reverse Hill–Sachs or McLaughlin defect). A normal axillary radiograph of the right shoulder is also shown for comparison (fig 3). Orthogonal views more clearly delineate the posterior dislocation and are required for accurate diagnosis with plain radiographs.

Figure 3

(a) A normal axillary radiograph of the right shoulder. (b) In the patient’s radiograph, the humeral head is impacted onto the posterior glenoid rim, with a resulting defect on the anteromedial humeral head (reverse …

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