Labrum acetabuli

Magnetic

resonance arthrography of the hip: technique and spectrum of findings in younger patients. Normal hip joint. Coronal fat-saturated T1-weighted arthro-MR image demonstrates a perilabral recess (white arrow). The superior labrum has a normal triangular shape and an homogeneous low signal (white arrowhead)

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Acetabular labrum acts to deepen the acetabulum and increase contact between the pelvis and the femoral head. Its exact biomechanical role remains to be fully elucidated.

Gross anatomy

The acetabular labrum is a C-shaped fibrocartilaginous structure with an opening anteroinferiorly at the site of the acetabular notch. Here it is bridged by the transverse ligament (thus forming the acetabular foramen beneath it). Elsewhere it is attached to the margins of the acetabulum.

The labrum is thickest posterosuperiorly and widest anterosuperiorly. It is triangular in cross-section. The fibrocartilage is arranged in three distinct layers:

external surface: circumferentially oriented layer with radial reinforcing filaments.

middle layer: dense lamellar collagenous layer

articular surface: randomly oriented fibrillar layer with chondrocytes

The capsule of the hip joint attaches to the margins or immediately adjacent to the acetabulum and transverse ligament. Superiorly the capsule's attachment is removed from the labrum by a few millimeters forming the perilabral sulcus. Anteriorly and posteriorly the attachment of the capsule is much closer to the base of the labrum, and thus the perilabral sulcus is commensurately smaller.

Radiographic features

Radiographically, the labrum is best evaluated with MR arthrography and should appear as a uniformly low signal triangular structure, although signal at the base of the labrum is variable. Additionally, intrasubstance heterogeneous signal is more frequently seen in older patients.

Related pathology

Labral pathology contributes to hip pain and the development of osteoarthritis of the hip. Labral lesions are more frequently seen in patients with 'abnormal' hip morphology including: