Table 2.

Types of Glenohumeral Dislocation

Type	Frequency	Plain radiographic appearances
Anterior	95%	Humeral head lies in a subcoracoid or subglenoid position on the frontal view or much more rarely subclavicular or intrathoracic; on the scapular Y view or axial view the humeral head is anterior to the glenoid. Associated findings are Hill-Sachs lesion and bony Bankart
Posterior	2–4%	On frontal view: “lightbulb” sign due to humerus being fixed in internal rotation, loss of half-moon overlap between humeral head and glenoid due to lateral displacement, rim sign: >6 mm between medial edge of humeral head and anterior margin of glenoid and the trough-line sign – line paralleling medial humeral head due to impaction fracture anteromedial humeral head i.e. reverse Hill-Sachs. Associated finding is avulsion fracture of lesser tuberosity
Inferior (Luxatio erecta)	<1%	The patient’s arm is fixed in abduction; humeral head lies subcoracoid or subglenoid with humeral shaft parallel to spine of scapula on frontal view. Associated findings: fracture acromion, inferior glenoid and greater tuberosity
Superior	<1%	Humeral head driven upward through rotator cuff. On frontal view humeral head overlies clavicle and acromion. Associated findings: fracture of clavicle, acromion, coracoid or greater tuberosity