SPECTRUM OF MRI FINDINGS IN GLENOHUMERAL INSTABILITY ABSTRACT ID NO: 50

INTRODUCTION The shoulder joint is a ball and socket type of joint that has two main stabilizers: the rotator cuff muscles (dynamic) the labral-ligamentous complex (static). The primary function of the rotator cuff muscles is to centralize the humeral head, limiting superior translation during abduction. The glenohumeral joint is the most commonly dislocated joint. The normal glenoid labrum height and width are 3 mm and 4 mm. The glenoid labrum is the ring of fibrocartilage that provides attachment to the glenohumeral ligaments and the capsule at the glenoid rim and deepens the glenoid fossa. The attachments of the glenohumeral ligaments and the long head biceps anchor to the labrum are stronger than the attachment of the labrum to the glenoid rim. Therefore, the glenoid labrum is commonly torn or avulsed when excessive force is applied to a glenohumeral ligament or the long head biceps

ANATOMY LATERAL VIEW OF THE GLENOID FOSSA WITH ITS LIGAMENTS

The glenohumeral ligaments (inferior, middle, and superior) are thickened bands of the joint capsule that extend from the inferior and anterior glenoid and glenoid labrum, to the anatomic neck region of the humerus. The inferior glenohumeral ligament (IGHL) is a hammock-like structure that attaches to the inferior glenoid, glenoid labrum, and the humeral neck. Thickened portions of the IGHL anteriorly and posteriorly are referred to as the anterior and posterior bands.

The middle glenohumeral ligament (MGHL) varies in thickness, shares a common origin with the SGHL & helps stabilize the shoulder anteriorly from 0-45 degrees of abduction and external rotation. The superior glenohumeral ligament (SGHL) is the smallest ligament and acts with the coracohumeral ligament to stabilize the glenohumeral joint It prevents posterior and inferior translation of the humeral head. MGHL CHL SGHL LH –BICEPS TENDON GL

On MRI the normal labrum demonstrates low signal intensity on all pulse sequences, due to the lack of mobile protons in this dense fibrocartilage. On cross sectional imaging, the normal labrum is most commonly triangular, but can also be round, cleaved, notched, flat, or absent DISCUSSION For localization purposes, the labrum is divided into six zones includes: superior, anterosuperior, anteroinferior, inferior, posteroinferior, and posterosuperior.

MRI diagnosis of labral tears is based on abnormalities in the signal intensity, morphology, and location (displacement) of the labrum. The labrum may be frayed, crushed, avulsed, or torn. Tears are classified by morphology, displaced or nondisplaced, and by location. Labral tears can extend into the biceps anchor as well as the glenohumeral ligaments. MRI criteria for diagnosing labral tears include : Surface irregularity, Increased signal within the substance of the labrum that extends to the labral surface , Fluid or contrast imbibed into the substance of the labrum , Labral avulsions. Secondary signs of labral tears include paralabral cysts , periosteal stripping and tearing, labral associated bone injuries .

Anterior Instability Posterior Instability

A Bankart lesion is a tear of the anterioinferior glenoid labrum with an associated tear of the anterior scapular periosteum, with or without associated fracture of the anterior inferior glenoid rim Classic Bankart lesion Bony Bankart lesion

A Perthes lesion is a variant of the Bankart, where the anterioinferior labrum is avulsed from the glenoid and the scapular periosteum remains intact but is stripped medially.

A BHAGL is a bony HAGL, that involves a bone fragment. A HAGL lesion is humeral avulsion of the glenohumeral ligament that occurs from shoulder dislocation, with avulsion of the inferior glenohumeral ligament from the anatomic neck of the humerus. A BHAGL is a bony HAGL, that involves a bone fragment. Reverse HAGL lesion: In posterior instability there is complete avulsion of the posterior attachment of the shoulder capsule and the glenohumeral ligament from the posterior humeral neck HAGL Reverse HAGL lesion

The GLAD lesion refers to glenolabral articular disruption, which involves a tear of the anterior inferior labrum with an associated glenoid chondral defect Glenoid avulsion of the glenohumeral ligaments (GAGL) implies an avulsion of the IGHL from the inferior pole of the glenoid, without an associated inferior labral disruption GLAD GAGL AVUL OF IGHL

The ALPSA lesion is characterized by a torn anteroinferior labrum with an intact but stripped periosteum and medial displacement of the labrum and inferior glenohumeral ligament Inferior ALPSA or cul-de-sac lesion is medial displacement of both the anterior-inferior labrum and the IGHL under the inferior neck of the glenoid ALPSA TORN ANTR INF LABRUM IGHL Inferior ALPSA AIL IGHL

Hill-Sachs lesion consists of bony injury to the posterosuperior humeral head as a result of inferior displacement (which occurred when the humeral head struck the anterior inferior glenoid during anterior dislocation). Reverse Hill-Sachs lesion consists of an anteromedial superior humeral head impaction fracture Bennett lesion is an extra- articular crescentic posterior ossification associated with posterior labral injury and capsular avulsion Hill-Sachs lesion Reverse Hill-Sachs lesion Bennett lesion

Rotator cuff interval tear do not appear as complete disruption of the fibers of its components but as thinning, irregularity, or focal discontinuity of the rotator interval capsule. Posterosuperior labral tear in association with a paralabral cyst may be seen in patients with posterior instability Rotator cuff interval tear Paralabral cyst

The SLAP lesion is an injury involving the superior aspect of the glenoid labrum, which includes the biceps tendon anchor. SLAP CLASSIFICATION Type II Type IV BHL with extension into biceps tendon

SLAP CLASSIFICATION TYPE VII TYPE V SLAP lesion with anteroinferior extension Superior labral tear with MGHL extension TYPE IX Fraying of MGHL global labral abnormality

CONCLUSION Anterior instability is the most common type of shoulder instability. It is associated with a Bankart lesion and its variants and abnormalities of the anterior band of the inferior glenohumeral ligament, whereas posterior instability is associated with reverse Bankart and reverse Hill- Sachs lesions. REFERENCES Neviaser TJ. The anterior labroligamentous periosteal sleeve avulsion lesion: a cause of anterior instability of the shoulder. Arthroscopy 1993; 9:17-21. Lynne S, Steinbach, Tirman Philip FJ, Peterfy Charles G, Feller John F. Philadelphia: Lippincott Raven; 1998. Shoulder magnetic resonance imaging. Waldt S. Burkart A, Imhoff AB, Bruegel M, Rummeny EJ, Woertler K. Anterior shoulder instability: accuracy of MR arthrography in the Classification of Anteroinferior labroligamentous injuries. Radiology 2005; 237:578-583. Bottoni CR, Franjs BR, Moore JH, DeBerardino TM, Taylor DC, Arciero RA. Operative stabilization of the posterior shoulder instability. Am J Sports Med. 2005;33:996–1002. [PubMed: 15890637] Vidal LB, Bradley JP. Management of posterior shoulder instability in the athlete. Curr Opin Orthop. 2006;17:164–71.