Anatomic Variants and Pitfalls of the Labrum, Glenoid Cartilage, and Glenohumeral Ligaments
Section snippets
Function/Biomechanics
The glenoid labrum acts as a passive stabilizer to the glenohumeral articulation by adding depth to the shallow glenoid fossa.3 It also serves as a primary attachment site for the GHLs, joint capsule, and long head of the biceps tendon. The labrum demonstrates considerable anatomic variability in its appearance, which may pose a diagnostic challenge to image interpretation.
The labral outline is ovoid in configuration, conforming to the underlying glenoid rim, and is most firmly attached to the
Anatomy and Histology
The articular surfaces of the glenoid fossa and the humeral head are lined by hyaline cartilage. Articular congruity of the glenohumeral joint is improved by normal alterations in the cartilage thickness. There is relative thinning of the articular cartilage of the glenoid centrally and thickening along the periphery. In contradistinction, the articular cartilage of the humeral head is thicker centrally and thinner near its margins.
A focal well-demarcated articular cartilage defect at the
Ligaments
The large size discrepancy between the small glenoid and the large humeral head affords the shoulder joint the largest range of motion in the human body.3 However, it also renders the joint inherently unstable and susceptible to dislocation and subluxation. Active and passive stabilizers serve to maintain stability of the shoulder.
The GHLs serve as important static stabilizers of the shoulder joint over a wide range of positions. Formed by localized thickenings of the glenohumeral joint
SGHL
The SGHL extends from the superior glenoid margin and base of the coracoid, just anterior to the biceps tendon and courses inferolaterally to the anterior humerus just superior to the lesser tuberosity at the anatomic neck. The SGHL is nearly invariably present, identified at arthroscopy in 97% of patients3 and in an arthrographic series by Palmer and colleagues45 in 98% of patients. On MR imaging, the SGHL can be well visualized on axial planes as a low–signal intensity structure arising from
MGHL
Of all the GHLs, the MGHL demonstrates the most variability.3 The ligament may be absent in up to 30% of patients.48 Initial arthroscopic studies of MGHL anatomy described an origin from the anterior margin of the scapula, just medial to the articular surface. The ligament then courses in an oblique inferolateral direction along the posterior margin of the subscapularis tendon and inserts on the neck of the humerus. In some patients, the ligament may blend with the joint capsule before
IGHL complex
The IGHL complex is composed of an anterior and posterior band and an intervening portion, the axillary recess. The complex is consistently present.55 The anterior band arises from the anterior glenoid rim/labrum at approximately the level of the midglenoid notch, between the 2-o’clock to 4-o’clock positions, which is more cranial than the origin of the posterior band, arising at the 7-o’clock to 9-o’clock position. The posterior band also inserts more medially than the anterior band and may be
Summary
MR imaging and MR arthrography remain the primary imaging modalities for evaluation of patients with suspected internal derangement of the shoulder. Accurate interpretation of these studies requires an understanding of the complex anatomy of the shoulder joint as well as the potential anatomic variants and imaging pitfalls that are routinely encountered. Although many of the variants and pitfalls have been extensively described in the radiologic and surgical literature, this body of knowledge
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The authors have nothing to disclose.