**1. Introduction**

The glenohumeral joint achieves the greatest mobility compared with all other joints in the human body. Due to its complex anatomy, its stability is conferred by a combination of bone, soft tissue and muscular structures. It is therefore the most commonly dislocated joint, with an overall incidence of approximately 17/100.000 per year (Kroner et al, 1989). The classification of shoulder instability is complex, depending on the cause (traumatic vs. atraumatic), degree (dislocation, subluxation, or microinstability), direction (anterior, posterior, inferior or multidirectional), and chronology (acute, chronic, or acute on chronic). Traumatic glenohumeral instability is defined as occurring after an inciting event that results in subjective or objective subluxation or dislocation that is reduced either spontaneously or by a health professional (Cadet, 2010). Atraumatic instability occurs as the sequel of generalized ligamentous laxity or repetitive motion, as in overhead throwing athletes. Inferior and multidirectional instabilities are less common than anterior and posterior ones and have been described to combine the presence of a sulcus sign or inferior subluxation of the humeral head with symptoms of pain or instability (Neer & Foster, 1980). Anterior shoulder instability accounts for 95% of acute traumatic dislocations. Although many patients who suffer an initial shoulder dislocation never experience a second episode of instability, a significant percentage present with recurrent instability that results in morbidity and decreased functionality in respect to the demands placed on the joint during everyday, occupational and athletic activities.
