[Shoulder instabilities. Radiological evaluation]

In case of anteromedial instability of the shoulder, the radiological investigation should start by comparative plain films including glenoid lateral views looking for a lesion of the anteroinferior glenoid margin of the scapula. If plain films are normal, CT arthrography of the shoulder is indicated looking for a lesion of the anteroinferior glenoid labrum. If no traumatic abnormality is present, a plain CT scan may sometimes show glenoid dysplasia, which is frequently bilateral. Posterior dislocation of the shoulder is less common and is obvious on plain films. The inventory of the lesions is established by CT arthrography. In case of multidirectional instability, the radiological investigation determines the preferential direction of instability, generally by means of dynamic manoeuvres.