18 Acetabular Labral Tear

CASE 18

Acetabular Labral Tear

Anthony G. Ryan and Peter L. Munk

Clinical Presentation

A patient reported recent onset of hip pain and “clicking” after a forceful twisting injury.

Figure 18A

Figure 18B

Figure 18C

Figure 18D

T1-weighted coronal oblique (Figs. 18A–18C) and sagittal (Fig. 18D) images after intra-articular injection of dilute gadolinium show linear high signal intensity extending from within the anterosuperior labrum to the surface, present over a series of contiguous slices.

Diagnosis

Acetabular labral tear.

Differential Diagnosis

The clinical presentation has a differential diagnosis, including

Snapping iliopsoas tendon
Osteonecrosis
Intra-articular disorders, such as pigmented villonodular synovitis (PVNS) and synovial osteochondromatosis

The imaging appearance has no differential diagnosis.

Discussion

Background

The acetabular labrum is a fibrocartilaginous ring applied to the outer acetabular fossa margin, serving to increase hip joint stability by deepening the fossa. The increased depth promotes development of negative hydrostatic pressure within the joint, further increasing the “hold” of the acetabulum on the femoral head. Injuries to this structure therefore have significant effects on the stability of the joint.

Etiology

Although trauma is the unifying cause in all cases, certain conditions predispose to developing early or severe labral tears, including femoral acetabular impingement, congenital/developmental hip dysplasias (Figs. 18E, 18F) and following posterior hip dislocation (Figs. 18G, 18H). In dysplasias, it is thought that tears occur as a degenerative phenomenon secondary to abnormal force redistribution within the joint.

The causative trauma is not necessarily severe, often involving a simple twisting or slipping mechanism, such as occurs when one tries to catch one’s balance on ice or a slippery floor, or recurrent low-grade trauma at the extremes of hip flexion.

Pathophysiology

The labrum is well enervated and thus is very painful when injured or chronically irritated. In addition to the physical instability induced by a defect in the labrum and consequent loss of uniform intra-articular pressure, injury to the abundant proprioceptive supply decreases the stability of the joint.

Figures 18E and 18F Coronal oblique (18E) and transaxial (18F) T1-weighted images of the left hip after intraarticular injection of gadolinium in a patient with congenital hip dysplasia, consequent joint degeneration and labral tears, demonstrating femoral head surface irregularity and truncation, and diffuse high signal intensity of the anterosuperior labrum and a more clearly defined linear high signal intensity tear extending to the surface of the midportion of the posterolateral labrum. 18G and 18H Coronal oblique (18G) and sagittal oblique (18H) T1-weighted images of the right hip after intra-articular injection of gadolinium in a patient after posterior hip dislocation shows a combined labral tear with a fracture of the underlying acetabular margin seen extending from the anterosuperior labral margin to the posterior margin, with a bony fragment projected posterior to the bony acetabulum.

The anterosuperior portion of the labrum is torn most frequently. The labrum is most commonly avulsed from the bony acetabulum rather than a true intrasubstance labral tear.

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