Primary impingement can be defined as impingement caused by outlet stenosis in the subacromial space in a stable shoulder. According to various authors, symptoms of impingement in the throwing athlete are often related to glenohumeral instabilitty. This secondary form of impingement can be defined as impingement secondary to instability of the shoulder. Different anatomic structures can be impinged internally or externally, probably depending on the motion and loading put on the shoulder during the painprovoking activity.