Characteristics of multidirectional instability for a simple diagnosis (one type of pathology accounts for all directions of instability) or complex diagnoses (more than one type of instability pathology account for the several directions of instability). ‘Single diagnosis’ means that the pathology creating the instability in both or all directions is the same. ‘Multiple diagnosis’ means that the pathology of each direction of instability is different. It follows that the treatment of a case in the multiple-diagnosis MDI set is different for each direction: an inferior capsular shift might be the appropriate intervention for the II component, but the III (muscle-patterning) component should also be considered, and almost universally should be treated first. Many patients experience satisfactory return of sufficient stability with successful treatment of the III component (which is easier in the un-operated shoulder) and choose not to proceed to capsular surgery. The numbers refer to numbers of shoulders studied.