Imaging description

Abduction and external rotation (ABER) of the shoulder (Figure 10.1), when used with MR arthrography, may result in greater sensitivity than conventional positioning in detecting partial thickness tears (Figures 10.2 and 10.3) of the rotator cuff as well as some types of labral tears (Figures 10.1 and 10.3). The most sensitive sign of detachment of the anterior inferior glenoid labrum after ABER positioning of the shoulder in MR arthrography may be the presence of a contrast material-filled gap between the labrum and glenoid.

Importance

ABER positioning increases the sensitivity of MR arthrography in detecting anterior labral tears, particularly non-detached ones found at or near the insertion of the inferior glenohumeral ligament.

Typical clinical scenario

Patients with anterior glenoid labrum tears may present with shoulder pain or anterior instability.

Differential diagnosis

In non-detached anterior glenoid labrum tears, defined as tears that spare the deep fibers of the inferior glenohumeral ligament and anterior scapular periosteum, contrast material fills a gap at the base of the anterior glenoid labrum but stops short of rounding at the corner of the glenoid. Findings suggestive of a Bankart lesion on ABER MR arthrograms include contrast material in a gap at the base of the anterior glenoid labrum, which is characteristically wider and deeper than that of non-detached tears, and less commonly, the presence of contrast material rounding the corner of the glenoid.

Teaching point

Tension on the anterior labral-ligamentous complex created by the ABER position facilitates characterization of the anterior glenoid labrum tear.