Labrum

-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. 
-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”. 
-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. 
-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. 
-These injuries have classic appearances, and are associated with multiple acronyms (such as ALPSA and SLAP) and eponyms (like the Hill Sachs deformity).

-For localization purposes, the labrum is divided into four zones, six zones, or according to the location on a clock face. 
-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.

A fat suppressed oblique sagittal T1 weighted MR arthrogram image, demonstrating the six labral zones of the glenoid labrum.

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.

A fat suppressed oblique coronal T2-weighted MR image demonstrates homogeneously low signal intensity in the normal superior labrum (arrow).

A fat suppressed axial gradient echo image demonstrates increased signal intensity in the anterior labrum that extends through the labrum to the articular and non-articular surfaces (arrowheads), consistent with an anterior labral tear.

A fat suppressed oblique coronal T1-weighted MR arthrogram image demonstrates contrast extending into the superior labrum, consistent with a superior labral tear (arrow).

A fat suppressed oblique coronal T2-weighted image demonstrates a superior labral tear (arrow) and associated paralabral cyst (arrowhead). (Rotator cuff tendinosis is also noted).

-Multiple acronyms and eponyms are used to describe labral, glenohumeral ligament, and associated shoulder injuries. 

-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. (Some radiologists and surgeons use the term Bankart lesion to describe all tears of the anterioinferior labrum.)

A fat suppressed axial proton density-weighted image of a classic Bankart lesion, with tears of the anterioinferior labrum (arrow) and the adjacent scapular periosteum (arrowhead).

Illustration depicting the components of the classic Bankart lesion consisting of a tear of the anteroinferior labrum (L) and periosteum (P). Inferior glenohumeral ligament (IGHL), humerus (H), and glenoid (G).

-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 fat suppressed axial T1-weighted MR arthrographic image of a Perthes lesion demonstrates an avulsed anteroinferior labrum (arrow). The scapular periosteum remains intact but is stripped medially (arrow head).

The Perthes is a Bankart variant in which the labrum (L) is torn and the periosteum is stripped (P) but remains intact. Inferior glenohumeral ligament (IGHL), humerus (H), and glenoid (G).

-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.

Fat suppressed oblique coronal T1-weighted MR arthrogram images of a HAGL lesion. The axillary pouch in a normal patient is typically "U" shaped. This patient's axillary pouch has an abnormal inverted "J" shape (arrowheads). There is fraying of the inferior glenohumeral ligament (arrow), and cortical irregularity along the humeral neck (short arrows) consistent with a humeral avulsion of the glenohumeral ligament.

-The GLAD lesion (20a) refers to glenolabral articular disruption, which involves a tear of the anterior inferior labrum with an associated glenoid chondral defect.

A gradient-echo axial MR image of a GLAD lesion. The anterior labrum is torn (arrowhead) and there is an adjacent glenoid chondral defect (arrow).

-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. Additional categories of SLAP tears were described by Maffet et al , Morgan et al , Resnick and Beltran. 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.

Figure 21:

A fat suppressed oblique coronal T2-weighted MR image demonstrates a Type II SLAP lesion. Note fluid signal extending through the superior labrum (arrow) consistent with a superior labral tear. (Rotator cuff tendinosis with a tiny interstitial tear is also noted.)

Figure 22:

A fat suppressed oblique coronal T1-weighted MR indirect arthrogram image demonstrates a Type IV SLAP lesion, with increased signal undercutting the superior labrum (arrow) and extending into the biceps tendon (arrowhead).

Figure 23:

A fat suppressed axial T1-weighted MR arthrogram image demonstrates a Type VII SLAP lesion. The superior labral tear (arrowheads), extends into the conjoined attachment of the superior and middle glenohumeral ligaments (arrow). A small paralabral cyst (short arrow)arises posterosuperiorly from the superior labral tear.

A fat suppressed oblique sagittal MR arthrogram image demonstrates a global labral abnormality (arrowheads) consistent with Type IX SLAP lesion. Also note tearing and fraying of the labral/glenoid attachment of the middle glenohumeral ligament (arrow).

-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.

Figure 25:

A fat suppressed oblique coronal T1 MR arthrogram of a sublabral recess. Contrast undercuts the normal labrum and follows the contour of the glenoid cartilage (arrow heads), but does not extend posterior to the biceps anchor.

-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.

Figure 26:

A fat suppressed T1-weighted MR arthrogram of a sublabral hole (arrow). Sublabral holes/foramina occur anterosuperiorly (1 o'clock to 3 o'clock position). Note the smoothly contoured, otherwise normal appearing anterior superior labrum (arrow head), and middle glenohumeral ligament (short arrow).

-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.

Figure 27:

An axial fat suppressed T1-weighted MR arthrogram of a Buford complex. Note absence of the anterior superior labrum (arrowhead) and a thick, cord-like middle glenohumeral ligament (arrow).

Conclusion

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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