The extreme positioning of the humerus in maximum external rotation and 90° of abduction can, over time, stretch the anterior capsule and ligaments, leading to anterior capsular laxity and resultant microinstability or even frank anterior humeral translation. Microinstability may be assessed clinically by a positive ''apprehension test'' in which the patient has a sense of apprehension as his or her arm approaches the ABER position. Posterosuperior or ''internal'' impingement, in which the posterior aspect of the supraspinatus tendon and the anterior aspect of the infraspinatus tendon are compressed against the postero-superior aspect of the labrum and the glenoid, may ensue as a result of micro-instability and anterior translation of the humeral head. Although this compression can be a normal finding with overhead movements [14-16], it may also produce posterior shoulder pain [17,18]. Internal impingement may be assessed clinically with the ''relocation test ofJobe,'' in which, with the arm in the ABER position, the examiner holds the humeral head and pushes it anteriorly to produce pain and then posteriorly to relieve the pain. This test reproduces the impingement of the supraspinatus and infraspinatus tendons on the posterosuperior glenoid rim that occurs from anterior humeral subluxation in a shoulder with lax anterior restraints [19-21]. Decreased range of motion may also be present and may be seen on clinical examination as loss of internal rotation (''glenohumeral internal rotation deficiency,'' defined relative to the contralateral nonthrowing arm), weakness of scapular retraction, and weakness of upward rotation of the humerus. These can all contribute to loss of control and velocity during the throw, referred to as the ''dead arm'' syndrome [22,23]. Microinstability may also allow superior translation of the humeral head, which may then impinge the supraspinatus and infraspinatus tendons against the acromion or clavicle; this is referred to as secondary impingement .
Internal impingement may lead to ''kissing'' lesions on the glenoid and humeral sides of the joint due to repetitive impaction. On the humeral side, the supraspinatus and infraspinatus tendons and greater tuberosity are affected, whereas on the glenoid side, the posterosuperior aspect of the labrum and sub-chondral bone are affected. Kaplan and colleagues , Giaroli and colleagues , and Giombini and colleagues  all found similar constellations of abnormalities on MR imaging. In the study of Giaroli and colleagues, all six of their patients with clinically and arthroscopically diagnosed internal impingement had undersurface tears of the supraspinatus or infraspinatus tendons (Fig. 1) and had posterosuperior labral pathologic conditions, such as abnormal signal, fraying, or frank tears . In a retrospective study of nine throwing athletes who had severe internal impingement, Kaplan and colleagues  found that all nine had posterosuperior labral lesions, eight with labral fraying and one with a tear, found on both MRI and arthroscopy. All had infraspinatus tendin-opathy, and three had supraspinatus tendinopathy. Similarly, in the prospective study by Giombini and colleagues  of 11 water polo players complaining of shoulder pain, posterosuperior labral injury and partial tears of the undersurface of the rotator cuff were detected in all 11 athletes on both MRI and arthroscopy. Rotator cuff tendinopathy and tears involve the posterior aspect of the supraspinatus tendon or the anterior aspect of the infra-spinatus tendon [17,18].
The bony changes that can occur in the posterior aspect of the greater tuber-osity include subcortical cysts subjacent to the attachment of the supraspinatus and infraspinatus tendons (Fig. 2), flattening or focal indentation of the humeral head mimicking a Hill-Sachs defect (Figs. 3 and 4), and bone marrow edema, whereas subchondral sclerosis may occur in the posterosuperior aspect of the glenoid (Fig. 5) [23-25]. In Kaplan's  nine cases, eight had sclerosis in the posterosuperior aspect of the glenoid, whereas in Giombini's study , four had erosions of the posterosuperior glenoid, and five had osteochondral defects in the posterior aspect of the humeral head on radiographs.
Fig. 1. Extensive articular surface tear of the supraspinatus tendon. Coronal fat-suppressed T2-weighted image shows extensive but shallow tearing of the articular surface of the supraspinatus tendon (arrows).
In addition, in the abducted and externally rotated position in the late cocking phase, the long head of the biceps tendon has a more vertical and posterior course and is twisted at its base. This causes a posteriorly directed torsional force on the labrum and can lead to shearing and peeling back of the labrum from the glenoid, producing superior labral anterior posterior (SLAP) tears .
Superior labral lesions were originally described in 1985 by Andrews and colleagues . SLAP tears were initially classified into four types in 1990 by Snyder and colleagues , but there are now at least 10 types . Type I lesions involve fraying of the superior aspect of the labrum and are usually not
Was this article helpful?
Everything you wanted to know about. How To Cure Tennis Elbow. Are you an athlete who suffers from tennis elbow? Contrary to popular opinion, most people who suffer from tennis elbow do not even play tennis. They get this condition, which is a torn tendon in the elbow, from the strain of using the same motions with the arm, repeatedly. If you have tennis elbow, you understand how the pain can disrupt your day.