Multidirectional instability: current concepts.

Multidirectional instability (MDI) of the shoulder is a complex problem that is not yet well understood. Instability in several directions is termed MDI, but the precise definition, classification, cause, and optimal method of treatment remains elusive. The cause appears to be multifactorial, with biochemical and biomechanical abnormalities present in shoulders with MDI. The biomechanical factors responsible for preventing MDI include bony architecture, concavity-compression from the deepening of the glenoid by the labrum, stability from the ligaments, primarily the inferior glenohumeral ligament complex and the superior capsular structures, and muscular control by use of force couples, especially stabilization of the scapula. Current recommended treatment is initially nonoperative, with aggressive physical therapy aimed at strengthening the rotator cuff and the scapular stabilizers. Patients who fail to respond to a nonoperative regimen often improve with surgical stabilization, which is usually an inferior capsular shift or a variant of that procedure. After this surgery immobilization of the operated shoulder for 6 to 8 weeks is recommended by most authors.