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Topic

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Acetabulum

The acetabulum is the large, cup-shaped cavity on the lateral aspect of the pelvis formed by the fusion of the ilium, ischium, and pubis. It articulates with the head of the femur, creating the hip joint. Its superior portion, called the lunate surface, is lined with articular cartilage and bears most of the weight during locomotion. The inferior part, the acetabular notch, is bridged by the transverse acetabular ligament.

The acetabular margin (rim) provides attachment for the acetabular labrum, which deepens the cavity and stabilizes the hip joint. The acetabular fossa, located centrally, is non-articular and contains fat and the ligamentum teres.

The acetabulum plays a crucial role in hip biomechanics, allowing mobility while maintaining stability. Clinically, it is a key site in fractures, congenital dysplasia, labral tears, femoroacetabular impingement (FAI), and osteoarthritis.

Synonyms

  • Hip socket

  • Acetabular cavity

  • Cotyloid cavity

Function

  • Forms the socket of the hip joint for articulation with femoral head

  • Bears body weight transmission during standing, walking, and running

  • Provides attachment to acetabular labrum and transverse acetabular ligament

  • Supports joint stability and mobility

MRI Appearance

T1-weighted images:

  • Bone cortex: hypointense (black)

  • Bone marrow: intermediate signal intensity

  • Cartilage: intermediate signal, well delineated from marrow

  • Useful for detecting marrow infiltration, fractures, and bone alignment

T2-weighted images:

  • Bone cortex: hypointense

  • Marrow: intermediate to bright signal depending on fat/water content

  • Cartilage: hyperintense lunate surface

  • Detects subchondral cysts, cartilage loss, and marrow edema

PD Fat-Saturated (Proton Density with Fat Suppression):

  • Bone cortex: remains dark hypointense

  • Bone marrow: fat suppression highlights subtle marrow edema as hyperintense

  • Labrum/cartilage defects: appear bright

  • Very sensitive for osteochondral injury, bone marrow edema, and labral tears

STIR:

  • Bone cortex: hypointense

  • Bone marrow: edema appears hyperintense, fat suppressed

  • Useful in trauma, stress fractures, inflammatory or neoplastic infiltration

T1 Post-Gadolinium (MR Arthrography with fat saturation):

  • Bone cortex/marrow: marrow enhances mildly, bone cortex remains dark

  • Cartilage and labrum: contrast outlines defects

  • Detects labral tears, synovitis, cartilage defects, and intra-articular pathology

3D T2-weighted Imaging:

  • Bone cortex: dark hypointense rim outlining acetabulum

  • Bone marrow: intermediate signal

  • Provides isotropic voxels for multiplanar reconstruction

  • Excellent for assessing acetabular version, morphology, and labral integrity

CT Appearance

Non-contrast CT:

  • Bone cortex: hyperdense, sharply outlined

  • Bone marrow: relatively hypodense compared to cortex

  • Excellent for fractures, dysplasia, retroversion, pincer lesions, or bone loss

CT Post-Contrast (CT Arthrography):

  • Bone cortex: unchanged, hyperdense

  • Bone marrow: enhancement depends on vascularity

  • Labrum/cartilage: joint contrast highlights tears or cartilage loss

  • Very useful when MRI is contraindicated

MRI image

Acetabulum MRI axial anatomy image-img-00000-00000

MRI image

Acetabulum MRI coronal anatomy image-img-00000-00000

CT image

Acetabulum CT axial image

CT image

Acetabulum CT coronal image

CT image

Acetabulum CT CORONAL

CT VRT 3D image

Acetabulum 3d

X Ray image

Acetabulum x ray anatomy labelled image-img-00000-00000