Navigating the Alphabet Soup of Labroligamentous Pathology of the Shoulder

The widespread use of eponyms and acronyms to describe labroligamentous findings in the shoulder has made interpretation of shoulder magnetic resonance imaging (MRI) reports challenging. We review and discuss the appearance of these lesions on shoulder MRI to help the orthopedic surgeon understand these entities as imaging findings.

Glenolabral articular disruption (GLAD) occurs secondary to impaction of the humeral head on the glenoid articular cartilage. There is a resultant defect in the glenoid articular cartilage, which extends to the glenoid labrum. A GLAD lesion is diagnosed only if the glenohumeral ligament and scapular periosteum remain intact¹ (Figure 1).

Complete detachment of the anteroinferior labrum with tearing of the anterior glenoid periosteum represents a Bankart lesion. Cartilaginous Bankart lesions are caused by an anterior glenohumeral dislocation with resultant avulsion of the anteroinferior labrum and disruption of the scapular periosteum because of acute traction on the anterior band of the inferior glenohumeral ligament (Figure 2). Anterior instability, caused by disruption of the anterior labroligamentous complex, results. Osseous Bankart lesions occur when the anterior displaced humeral head impacts the anterior inferior glenoid rim, causing a fracture (Figure 3). This loss of the glenoid articular surface area can result in glenohumeral instability. Posterior shoulder dislocations can result in corresponding findings in the posterior inferior glenoid labrum (reverse Bankart lesion) and anterior medial humeral head (reverse Hill-Sachs lesion) (Figure 2).

A variant of the Bankart lesion is the anterior labroligamentous periosteal sleeve avulsion (ALPSA). This refers to a medially displaced tear of the anterior labrum with intact periosteal stripping along the medial glenoid²with medial rotation and inferior displacement of the anterior inferior labrum along the scapular neck. An ALPSA lesion can heal via the intact periosteal blood supply. If not repaired, anterior instability will result because of malposition of the labrum, causing a patulous anterior capsule.³ When a corresponding lesion occurs in the posterior labrum because of a posterior dislocation, it is called a posterior labrocapsular periosteal sleeve avulsion (POLPSA) (Figure 4).

Another variant of the Bankart lesion is the Perthes lesion, which is a nondisplaced tear of the anteroinferior labrum with periosteal stripping. This differs from the ALPSA because the detached labrum and periosteum are held in anatomic position, possibly making the lesion difficult to detect on magnetic resonance arthrography (MRA).³ Obtaining images in the abduction external rotation (ABER) position exerts traction on the anterior inferior joint capsule and may make the Perthes lesion more conspicuous.⁴ When this occurs in the posterior labrum, it is called a reverse Perthes lesion (Figure 5).

In a patient with anterior glenohumeral instability without a Bankart lesion, pathology of the anterior band of the inferior glenohumeral ligament (IGHL) at its humeral attachment must be suspected. Humeral avulsion of the IGHL (HAGL) or its variants can be overlooked on arthroscopy. HAGL is diagnosed on MRA when the normally U-shaped IGHL takes on a J-shape, and joint fluid extravasates across the torn humeral attachment (Figure 6). If there is an avulsed bony fragment from the medial humeral neck, the lesion is termed a bony HAGL (BHAGL). In addition to the findings of a HAGL, a BHAGL shows the osseous fragment and donor site on MRI. Since a BHAGL is a bony avulsion, it can even be suggested on radiography if a bony fragment is seen adjacent to the medial humeral neck.⁵ These lesions are highly associated with other shoulder injuries, particularly Hill-Sachs deformities and subscapularis tendon tears, and it is imperative, therefore, to search for additional injuries if a HAGL-type injury is seen.⁶

A more uncommon type of HAGL can occur in the setting of posterior capsulolabral injury. A posterior-band IGHL avulsion from the humerus (PHAGL) has similar imaging findings to a HAGL, except that it involves the posterior band of the IGHL. PHAGLs are usually not associated with an acute injury and are thought to be related to repetitive microtrauma, perhaps since the posterior band of the IGHL is the thinnest portion of the IGHL complex.⁷

A Kim lesion is an arthroscopic finding described in patients with posterior instability as a superficial defect at the undersurface of the posterior labrum and adjacent glenoid cartilage without detachment or extension to the chondrolabral junction.⁸ It is, by its nature, a concealed finding on routine MRI but can be more conspicuous in FADIR (flexed, adducted, internally rotated) positioning on MRA, which exerts traction on the posterior joint capsule, allowing intra-articular contrast to fill the tear (Figure 7).

This list describes several of the most commonly encountered acronyms in shoulder MRI. A review of SLAP (superior labrum anterior to posterior) lesions was described in a previous article in the journal’s Imaging Series.⁹ A thorough understanding of these lesions is helpful in interpreting reports and determining the appropriate treatment for patients with shoulder injuries.