Diagnosis:
Posterior shoulder dislocation
Discussion:
Trough line is seen with posterior shoulder dislocation. When the humeral head is
forced posteriorly in internal rotation, the anterior aspect of the humeral head is driven
against the posterior glenoid rim. With sufficient force, the head will sustain a
compression fracture. In many cases of posterior dislocation of the shoulder, two parallel
lines of cortical bone can be seen. The outer (more medial) cortical line represent the
medial cortex of the humeral head, while the other line represents the margin of a
"trough" like impaction fracture.
A
B
References: