Anterior Instability: What to Look for.

Most first-time anterior glenohumeral dislocations occur as the result of trauma. Many patients suffer recurrent episodes of anterior shoulder instability (ASI). The anatomy and biomechanics of ASI is addressed, as is the pathophysiology of capsulolabral injury. The roles of imaging modalities are described, including computed tomography (CT) and MR imaging with the additional value of arthrography and specialized imaging positions. Advances in 3D CT and MR imaging particularly with respect to the quantification of humeral and glenoid bone loss is discussed. The concepts of engaging and nonengaging lesions as well as on-track and off-track lesions are examined.