Clinical History: A 30 year old male with shoulder pain and instability. Fat-suppressed (1a) axial proton density and (1b) T2-weighted oblique coronal images are provided. What are the findings? What is your diagnosis?
ALPSA and Hill Sachs deformities, secondary to acute anterior glenohumeral dislocation.
An ALPSA lesion is an anterior labroligamentous periosteal sleeve avulsion. ALPSA is a variation of the Bankart lesion where the anterior inferior labrum is torn and the labrum, inferior glenohumeral ligament and intact scapular periosteum are stripped and displaced medially on the glenoid neck. 1, 2
The glenohumeral joint is a synovial-lined ball-in-socket joint that has the greatest range of motion of any joint in the human body. The glenohumeral joint is the most commonly dislocated joint, attributed to the much larger articular surface area of the humeral head and the smaller, shallow glenoid fossa.3,4,5 The glenoid labrum is a fibrocartilaginous cuff surrounding the glenoid fossa. The labrum deepens the fossa and increases the articular surface area of the glenoid. The osseous rim of the glenoid and the fibrocartilaginous labrum are sites of attachment for the glenohumeral ligaments and long head biceps tendon, which can be injured individually or in tandem.
Glenohumeral stability is provided by dynamic and static “restraints” (4a). Dynamic restraints include the rotator cuff and the long head biceps brachii tendon. Static restraints include the glenohumeral ligaments, glenohumeral joint capsule (including the rotator cuff interval capsule), the coracohumeral ligament, the glenoid labrum, and the bones.2,4,6,22 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.5 Therefore, the glenoid labrum is commonly torn or avulsed when excessive force is applied to a glenohumeral ligament or the long head biceps.3,7-11 These injuries have classic appearances, and are associated with multiple acronyms (such as ALPSA and SLAP) and eponyms (like the Hill Sachs deformity).
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, protecting against extreme range of motion.
The inferior glenohumeral ligament (IGHL) (5a,6a) 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. Anterior inferior shoulder dislocation is the most common cause of shoulder instability, and the anterior band of the inferior glenohumeral ligament is believed to represent the major passive stabilizer of the glenohumeral joint.
The middle glenohumeral ligament (MGHL) (7a) is the most variable of the glenohumeral ligaments. It varies in thickness and is associated with labroligamentous anatomic variations such as in the Buford complex. The MGHL can share a common origin with the superior glenohumeral ligament, can be absent in approximately one tenth to one third of shoulders, and functions to help stabilize the shoulder anteriorly from 0-45 degrees of abduction and external rotation. 5,7,20
The superior glenohumeral ligament (SGHL) (8a) is the smallest of the glenohumeral ligaments and acts with the coracohumeral ligament to stabilize the glenohumeral joint and prevent posterior and inferior translation of the humeral head. The SGHL can have a common attachment with the long head biceps anchor to the superior glenoid/superior labrum. The long head biceps tendon can also attach along the anterior, posterior, or along both the anterior and posterior superior glenoid/labrum.
For localization purposes, the labrum is divided into four zones, six zones, or according to the location on a clock face (9a). The four zones are superior, anterior, inferior, and posterior. Further subdivision of the labrum into six zones includes: superior, anterosuperior, anteroinferior, inferior, posteroinferior, and posterosuperior. By convention, when utilizing the clock face, the mid superior labrum is denoted as 12 o’clock and the mid inferior labrum as 6 o’clock. There is controversy regarding 3 o’clock and 9 o’clock, as radiologists tend to classify the anterior labrum as 3 o’clock regardless of side, whereas some of the orthopaedic literature assumes 3 o’clock as anterior at the right shoulder but posterior at the left shoulder. For this reason, we favor utilizing a descriptive method of localization, utilizing zones and the use of equator as a designation of the mid anterior or posterior labrum.
The normal labrum (10a,11a) 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.12,19
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 (12a), fluid or contrast imbibed into the substance of the labrum (13a), and labral avulsions. Secondary signs of labral tears include paralabral cysts (14a), periosteal stripping and tearing, labral associated bone injuries such as Hill Sachs and Osseous Bankart lesions, and hyaline cartilage injuries such as the GLAD lesion.
Multiple acronyms and eponyms are used to describe labral, glenohumeral ligament, and associated shoulder injuries. A Bankart lesion (15a) 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. (Some radiologists and surgeons use the term Bankart lesion to describe all tears of the anterioinferior labrum.)
A Perthes lesion (17a) 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 HAGL lesion (19a) 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, or a HAGL lesion that involves a bone fragment.
The GLAD lesion (20a) refers to glenolabral articular disruption, which involves a tear of the anterior inferior labrum with an associated glenoid chondral defect.
The POLPSA lesion is a posterior labrum periosteal sleeve avulsion lesion. The POLPSA lesion is associated with posterior glenohumeral instability and most commonly occurs with posterior dislocation. In the POLPSA lesion, the posterior labrum is torn and the posterior scapular periosteum is intact but stripped from the posterior glenoid. The POLPSA lesion is similar to the ALPSA lesion, however it occurs posteriorly
SLAP (21a,22a,23a,24a) is an acronym for superior labral tears, that propagate anterior and posterior in reference to the biceps anchor. Originally, SLAP lesions were classified by Snyder et al, based on arthroscopic evaluation.13 Additional categories of SLAP tears were described by Maffet et al , Morgan et al , Resnick and Beltran.14,15,16 Although the classification of SLAP tears is useful in terms of prognosis and treatment, a careful description of the type and location of labral tear can provide equivalent information.
Labroligamentous anatomic variants can mimic pathology, but their appearance and typical location can aid in making the correct diagnosis. Labral variations most commonly ocurr anterosuperiorly, at the 11 o’clock to 3 o’clock position. The sublabral recess (25a) or sulcus is seen at the 11 o’clock to 1 o’clock position, at the junction of the biceps labral complex, but it does not extend posterior to the biceps anchor. The sublabral recess is differentiated from a labral tear by the specific location, the smooth margin, and the fact that it follows the contour of the glenoid. Sublabral recess occurrence increases with increasing patient age, suggesting that sublabral recesses are an age dependant degenerative phenomenon.17
A sublabral hole, or foramen (26a), occurs between the anterosuperior labrum and the adjacent glenoid cartilage at the 12 o’clock to 3 o’clock position. It occurs most commonly at the 2 o’clock position, and in patients with a “pear shaped” glenoid.
The Buford complex (27a) is an anatomic variant that is seen anterosuperiorly, when the anterosuperior portion of the labrum is absent and the middle glenohumeral ligament is thick and cordlike.18
Shoulder pain and instability are common orthopedic problems. Although there are many causes of shoulder pain and instability (including fractures and rotator cuff tears), injuries to the glenohumeral ligaments, labrum, and biceps labral complex are often the cause. Its high spatial resolution, excellent image contrast, and multiplanar capabilities make MRI an excellent tool in the evaluation of the labrum. MR allows accurate depiction of the size and location of labral tears and their associated capsular and glenohumeral ligament injuries. Normal variants that can mimic pathology are also well depicted on MR imaging.
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Special thanks to Stadnick ME, Awh MH, Flemming DJ, Overdeck KH, and Caswell KL