Instability

Two main categories of instability include multidirectional atraumatic instability and traumatic instability [11]. Multidirectional instability usually is seen in young patients, is often bilateral, and is believed to be because of capsular laxity, which is not evaluated well with MRI. These patients typically are not sent for imaging [12].

Traumatic instability most commonly occurs after a shoulder dislocation and is usually unidirectional. Because anterior shoulder dislocation is much more common than posterior dislocation, recurrent anterior instability is more common than posterior instability. Traumatic anterior dislocation often results in tearing of the anterior inferior labrum (Bankart lesion) and in other cases there may be fracture of the anterior inferior glenoid rim (Bankart fracture) (Fig. 10). The inferior glenohumeral ligament is the main passive stabilizer of the gleno-humeral joint and its anterior band attaches to the anterior inferior labrum (Fig. 11). Tears of the anterior inferior labrum or fracture of the glenoid rim at this site destabilizes the glenohumeral ligament anchor. The inferior gleno-humeral ligament becomes incompetent and the shoulder becomes unstable

Shoulder Hagl
Fig. 10. Glenoid rim fracture following dislocation in 46-year-old patient. On PD axial image, the anteroinferior glenoid shows cortical discontinuity and medial displacement indicating fracture. The labrum (arrow) remains attached to the glenoid rim.

(Fig. 12). A similar situation may occur after posterior dislocation with rupture of the posterior band of the inferior glenohumeral ligament, posterior labral tear, and recurrent posterior instability.

Rarely, the inferior glenohumeral labral-ligamentous complex may rupture at a site other than the labrum or glenoid. One example of this situation is humeral avulsion of the inferior glenohumeral ligament (HAGL lesion) (Fig. 13). Although uncommon, a HAGL lesion is identified best in the acute setting before resolution of edema and hemorrhage. It may be important to identify on MRI because it may be difficult to see during arthroscopy and can cause significant shoulder instability.

Tears also may occur in the superior labrum. Typically these superior labral tears do not cause physical signs of instability; however, patients may have pain

Picture Rotator Cuff And Labrum

Fig. 11. Normal inferior labral-ligamentous complex. T1-weighted arthrographic MR axial image shows the inferior glenohumeral ligament (arrow) at its attachment site to the anteroinferior glenoid labrum. Labral tear in this location is closely associated with anterior instability because of incompetence of the inferior glenohumeral ligament. H, humerus.

Fig. 11. Normal inferior labral-ligamentous complex. T1-weighted arthrographic MR axial image shows the inferior glenohumeral ligament (arrow) at its attachment site to the anteroinferior glenoid labrum. Labral tear in this location is closely associated with anterior instability because of incompetence of the inferior glenohumeral ligament. H, humerus.

Anteroinferior Labral Tear

Fig. 12. Anteroinferior glenoid labral tear in 20-year-old patient with anterior instability. Following intra-articular injection of contrast material, fat-suppressed T1-weighted axial image shows contrast material partially undercutting the anteroinferior glenoid labrum (arrow), which is mildly displaced from the glenoid rim. Contrast also undercuts adjacent articular cartilage indicating delamination and flap formation. G, glenoid.

Fig. 12. Anteroinferior glenoid labral tear in 20-year-old patient with anterior instability. Following intra-articular injection of contrast material, fat-suppressed T1-weighted axial image shows contrast material partially undercutting the anteroinferior glenoid labrum (arrow), which is mildly displaced from the glenoid rim. Contrast also undercuts adjacent articular cartilage indicating delamination and flap formation. G, glenoid.

and a subjective feeling of instability. Superior labral tears may extend into the biceps anchor or may be caused by avulsion because of stress on the biceps tendon. This latter scenario often is seen in overhead-throwing athletes, swimmers, and tennis players. Repetitive overhead motions in these athletes causes traction on the biceps tendon, which is anchored on the superior labrum. The chronic stress on this bicipital-labral complex ultimately leads to tearing of the biceps anchor. A superior labral tear that involves the biceps anchor is more likely to be considered for surgical repair [13].

Rotator Cuff Anchor

Fig. 13. Humeral avulsion of the inferior glenohumeral ligament following anterior dislocation in a 38-year-old patient. Fat-suppressed T2-weighted oblique coronal image (A) shows edema or hemorrhage distal to the axillary pouch and inferior glenohumeral ligament, which is discontinuous at its expected attachment site to the humerus (arrow). On fat-suppressed T2-weighted axial image (B), the anteroinferior labral-ligamentous complex remains attached normally to glenoid rim (arrow). G, glenoid; H, humerus.

Fig. 13. Humeral avulsion of the inferior glenohumeral ligament following anterior dislocation in a 38-year-old patient. Fat-suppressed T2-weighted oblique coronal image (A) shows edema or hemorrhage distal to the axillary pouch and inferior glenohumeral ligament, which is discontinuous at its expected attachment site to the humerus (arrow). On fat-suppressed T2-weighted axial image (B), the anteroinferior labral-ligamentous complex remains attached normally to glenoid rim (arrow). G, glenoid; H, humerus.

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