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Inferior rim of acetabulum

The inferior rim of the acetabulum forms the lower margin of the acetabular socket and contributes to the containment and stability of the femoral head within the hip joint. It is a key structural component of the pelvic acetabulum and plays an important role in load transmission and joint congruency.

It is an important anatomical landmark in orthopedic anatomy, hip arthroscopy, trauma assessment, and imaging of the hip joint.

Synonyms

  • Inferior acetabular margin

  • Inferior acetabular rim

Location

  • Situated at the lower margin of the acetabulum

  • Forms the inferior boundary of the acetabular cavity

  • Located between the anterior and posterior acetabular rims

  • Adjacent to the acetabular notch inferiorly

  • Faces the femoral head and inferior joint space

Anatomical components

  • Osseous acetabular rim:

    • Curved bony margin of the acetabulum

  • Acetabular notch (inferiorly):

    • Interruption in the rim bridged by the transverse acetabular ligament

  • Labral attachment zone:

    • Inferior acetabular labrum attaches to the rim

  • Adjacent ligamentous structures:

    • Transverse acetabular ligament

    • Ligament of head of femur (ligamentum teres) nearby

Relations

Superiorly:

  • Acetabular cavity and lunate surface

Inferiorly:

  • Acetabular notch

  • Transverse acetabular ligament

Anteriorly:

  • Anterior acetabular rim and pubic portion of the acetabulum

Posteriorly:

  • Posterior acetabular rim and ischial portion of the acetabulum

Medially:

  • Pelvic cavity

Laterally:

  • Femoral head

X-ray appearance

Plain radiographs (AP pelvis and oblique views):

  • Inferior rim: Seen as the inferior curvilinear bony contour of the acetabulum

  • Acetabular notch: Appears as a small interruption at the inferior margin

  • Joint congruency: Assessed by relationship to femoral head

  • Symmetry: Compared bilaterally for contour and alignment

CT appearance (Pre-contrast)

Non-contrast CT (bone window):

  • Inferior acetabular rim: Sharp, corticated bony margin

  • Acetabular notch: Clearly visualized inferior discontinuity

  • Trabecular pattern: Normal cancellous bone architecture

  • Spatial definition: Precise evaluation of rim contour and thickness

  • Relationship to femoral head: Accurately depicted in axial and sagittal planes

MRI appearance

T1-weighted images:

  • Cortical rim: Low signal intensity

  • Adjacent marrow: High signal within the acetabular bone

  • Inferior labrum: Low-signal triangular structure attached to rim

T2-weighted images:

  • Cortical bone: Low signal

  • Joint fluid: High signal outlining the inferior rim

  • Labrum: Low signal against bright fluid

STIR:

  • Marrow fat: Suppressed signal

  • Inferior rim contour: Clearly delineated

  • Joint fluid: Bright signal in the inferior recess

Proton density fat-saturated (PD FS):

  • Cortical margin: Low signal

  • Joint fluid: Bright signal

  • Labrum and ligamentum teres: Well visualized as low-signal structures

CT VRT 3D image

Inferior rim of acetabulum 3d

CT image

Inferior rim of acetabulum ct axial

MRI image

Inferior rim of acetabulum mri anatomy labelled image-img-00000-00000