• Diagnosis
• Evidence based
• Rehabilitation
• Shoulder

The aim of this editorial is to discuss the pros and cons of some of the current classification systems of shoulder instability, with special emphasis on instability in more than one direction, and to summarise the basis for future clinical reasoning and research.

The term ‘multidirectional instability’ (MDI) is commonly used in adolescents and young adults, who can sometimes voluntarily subluxate their glenohumeral joints. They report pain, instability and shoulder disability, and present with symptomatic abnormal movement of the joint in two or more directions; the abnormal movement may predominate in one direction. The joint laxity may be congenital (in which case, it is often bilateral), or may due to the microtrauma of highly repetitive end-range movements, for example, in overhead athletes.