Musculoskeletal ImagingLabrum
an anatomic structure consisting of circumferential cartilaginous structures occurring around certain joints and attaching to the peripheral part of a joint surface. The hip and glenohumeral joint are among the joints with labra. Their function is to help enlarge or deepen the joint cavity. Usually labra are triangular in cross-section.
The glenoid labrum is a cuff of fibrous and fibrocartilaginous tissue surrounding the glenoid cavity. Part of its function is to provide stability to the glenohumeral joint, and it may play a role in dislocations of this joint. MR imaging is of value in assessment of labral abnormalities, such as tears, pseudotears and degeneration. One criterion for labral tear is the glenoid labrum ovoid mass GLOM or GLOM. The glenoid labrum is also involved in the ALPSA lesion (anterior labroligamentous periosteal sleeve avulsion) and the SLAP lesion (superior labral anterior and posterior lesion).
In the hip, abnormalities of the acetabular labrum include tears and cystic degeneration. Subchondral cysts of the acetabulum and osteoarthritis of the hip may be seen in some patients with labral tears. Arthrography is useful in defining these lesions. On MR images cysts appear as well-defined masses of low signal intensity on T1-weighted spin-echo images but of high signal intensity on T2-weighted images. Children with developmental dysplasia of the hip DDH also exhibit alterations in this structure. In some infants, the labrum grows inwardly, hypertrophies and fuses with the joint capsule (forming a limbus). Contrast arthrography can reveal subluxation or complete dislocation of the hip, during which the labrum may be elevated and flattened against the pelvis. Normally the labrum has a "rose thorn" appearance, but this may be lost if the limbus becomes folded on itself and lies within the acetabulum.
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