The patient had traumatic posterior shoulder dislocation with the development of the following:
- Reverse Hill Sachs lesion and Trough line sign as evident by depression of the anteromedial aspect of humeral head.
- Posterior labral tear with avulsion of the posteroinferior labrum which appears hypertrophied. It remains attached to the capsule and periosteum (periosteal sleeve avulsion).
- Posterior de-centering of the humeral head relative to the glenoid consistent with posterior instability.
- Marrow oedema of the glenoid.
- Os acriomiale as an incidental finding.
Diagnosis: Posterior labroligamentous periosteal sleeve avulsion (POLPSA) and posterior shoulder instability secondary to posterior shoulder dislocation.