Ans: C (Post dislocation of shoulder) Ref: Apley's System of Orthopaedics and Fractures. 9th ed. Explanation:Light bulb appearance - Seen due to internal rotation of humeral head in posterior dislocation of the shoulder.When the humerus dislocates posteriorly, it also internally rotates such that the head contour projects like a light bulb when viewed in a shoulder AP radiograph.Anterior dislocation of shoulder occurs from excessive external rotation of the shoulder (especially in abduction).Risk factors of Posterior shoulder dislocation of the shoulder occurs from:o Excessive internal rotation,o Following seizure episode,o Following electrocution.o In both seizure and electrocution, excessive contraction of the stronger muscles of the upper back causes pull of the humeral head backward causing dislocation.* Normal appearance of shoulder in X-ray.* Light bulb appearance of humeral head in X-ray due to internal rotation of the humeral head in posterior dislocation.Note: associated with anterior shoulder dislocation - Fracture of the greater tuberosity. associated with posterior shoulder dislocation - Fracture of the lesser tuberosity.Also Note:Standard Radiographs for Trauma of Shoulder:Shoulder - AP (in external rotation)Scapula Y viewAdditional Views:AP view (in internal rotation or in neutral position).Axial view.Shoulder LesionsHill-Sachs lesion: Compression fracture in the posterolateral humeral head, occurring secondary to recurrent- anterior shoulder dislocations, due to impingement of the humeral head against the anteroinferior part of the glenoid. It commonly associated with a Bankart lesion of the glenoid.Reverse Hill-Sachs lesion/ McLaughlin lesion: Impaction fracture of antero-medial aspect of humeral head following posterior dislocation of the humerus. Occurs due to impingement of humeral head against the posterior rim of the glenoid.Bankart lesion: Detachment of the anterior inferior iabrum from the glenoid; results from anterior shoulder dislocation.Bony Bankart lesion: Avulsion of a fragment of glenoid rim along with the Iabrum.Reverse Bankart lesion: Detachment of the posteroinferior Iabrum; results from posterior shoulder dislocation.Perthes lesion of shoulder: Detachment of the anteroinferior Iabrum with medially stripped but intact periosteum.SLAP tear {Superior labral anterior posterior tear): Tear of the superior Iabrum in the region of the insertion of the biceps.