The population between 18 and 30 years is the most discussed collective for shoulder instabilities. This young and active generation shows the highest incidence rate over all generations. According to Zacchilli et al. [15] who investigated 8940 shoulder dislocations, the incidence rate was 47.76 per 100,000 person-years at risk in the age between 20 and 30 compared to the reported general incidence rate of 3.1–23.9 [4, 6, 13, 15]. A much higher incidence rate was noted for male patients (79.2) when compared to females (14.8) [15]. Overall sports (especially football and basketball) and recreation-related dislocations caused 48.3% of all injuries with a significant higher rate for males [15]. It is still unknown why there is such a big difference between male and female and if neuromuscular factors, the mechanism of dislocation, or the type of repositioning may have an influence [10]. It has to be noted that most of the contact and collision sports may be affected by a gender bias, as most of them are performed by male athletics and some contact sports do have sex-modified regulations for women [5, 10].

Due to the high incidence rate, the recurrence rate of conservative treated patients in these active populations is high, too, with a rate up to 56% (range 23–29 years of age) [2, 3, 9, 11], but the systematic review by Olds et al. [9] found that this rate might be too high, due to very strict inclusion and exclusion criteria, which may not represent the general population. Additionally it has been shown that surgical stabilization is significantly reducing the recurrence rate, and therefore it is necessary to identify which patient would benefit from early surgical treatment compared to conservative treatment [3, 12, 14].

Several studies have tried to identify the risk factors, but due the inhomogeneous reported data of dislocation direction, time to first presentation, mechanism of injury, and many more factors, it is hard to compare the results. To encounter this challenge, several scores have been developed such as the instability severity index score or the FEDS (frequency, etiology, direction, and severity) classification system with good intra- and inter-rater reliability in order to simplify the documentation of a shoulder instability event and to achieve comparable data [1, 7]. Interestingly the FEDS classification did correlate with patient requiring surgical stabilization [8]. In the same study, the risk factors for recurrent instability established by the instability severity index score were similar to the reported factors such as involvement in contact sports, hyperlaxity, Hill-Sachs lesions, or loss of inferior glenoid bone after arthroscopic treatment. Especially frequency and etiology showed to be good predictors for surgery [8].