Diagnosis and treatment of posterior shoulder instability based on the ABC classification

center dot Posterior shoulder instability (PSI) is less common than anterior shoulder instability, accounting for 2-12% of total shoulder instability cases. center dot However, a much higher frequency of PSI has been recently indicated, suggesting that PSI accounts for up to 24% of all young and active patients who are surgically treated for shoulder instability. center dot This differentiation might be explained due to the frequent misinterpretation of vague symptoms, as PSI does not necessarily present as a recurrent posterior instability event, but often also as mere shoulder pain during exertion, limited range of motion, or even as yet asymptomatic concomitant finding. center dot In order to optimize current treatment, it is crucial to identify the various clinical presentations and often unspecific symptoms of PSI, ascertain the causal instability mechanism, and accurately diagnose the subgroup of PSI. center dot This review should guide the reader to correctly identify PSI, providing diagnostic criteria and treatment strategies.