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Obturator foramen

The obturator foramen is a large oval opening in the anteroinferior part of the pelvis formed by the pubis and ischium. It is mostly closed by the obturator membrane, leaving a small superior opening, the obturator canal, through which the obturator nerve and vessels pass.

It is an important bony landmark in pelvic anatomy, orthopedic surgery, hernia assessment, and cross-sectional imaging of the pelvis.

Synonyms

  • Foramen obturatum

  • Obturator aperture

Location

  • Located in the anteroinferior part of the bony pelvis

  • Formed by the pubic bone anteriorly and the ischial bone posteriorly

  • Inferior to the acetabulum

  • Lateral to the pubic symphysis

  • Superior to the ischial tuberosity

Anatomical components

  • Bony margins:

    • Superior pubic ramus

    • Inferior pubic ramus

    • Body of the ischium

    • Ramus of the ischium

  • Obturator membrane:

    • Fibrous sheet covering most of the foramen

  • Obturator canal:

    • Small opening at the superolateral margin

    • Transmits obturator nerve, artery, and vein

Relations

Superiorly:

  • Acetabulum

  • Hip joint

Inferiorly:

  • Ischial tuberosity

  • Perineal region

Medially:

  • Pubic symphysis

  • Urinary bladder (deep pelvic relation)

Laterally:

  • Hip joint capsule

  • Obturator internus muscle

Anteriorly:

  • Pectineus muscle

  • Anterior pelvic wall

Posteriorly:

  • Obturator internus muscle

  • Pelvic sidewall

Structures associated with the obturator foramen

  • Obturator membrane

  • Obturator canal

  • Obturator nerve

  • Obturator artery and vein

  • Obturator internus muscle (internal surface)

  • Obturator externus muscle (external surface)

X-ray appearance

Pelvic radiographs (AP view):

  • Obturator foramen: Large oval radiolucent opening on each side of the pelvis

  • Margins: Smooth, well-corticated bony outlines

  • Symmetry: Normally symmetric bilaterally

  • Relationship: Inferior to the acetabula and lateral to the pubic symphysis

CT appearance

Pre-contrast CT:

  • Foramen: Well-defined bony defect with smooth cortical margins

  • Bony boundaries: Clearly visualized pubic and ischial components

  • Obturator canal: Small notch at the superolateral margin

  • Soft tissues: Obturator muscles seen lining the internal and external surfaces

  • Pelvic alignment: Symmetry of foramina assessed easily

MRI appearance

T1-weighted images:

  • Cortical bone: Low signal intensity outlining the foramen

  • Bone marrow: High signal within pubic and ischial marrow

  • Obturator membrane: Low-signal linear structure

  • Obturator muscles: Intermediate signal

T2-weighted images:

  • Bone cortex: Low signal

  • Muscles: Intermediate-to-slightly high signal

  • Obturator canal contents: Tubular structures of intermediate signal

STIR:

  • Bone marrow: Fat-suppressed low-to-intermediate signal

  • Muscles and soft tissues: Intermediate signal

MRI image

Obturator foramen mri anatomy Location and Imaging Appearance -img-00000-00000

CT image

Obturator foramen ct anatomy Location and Imaging Appearance -img-00000-00000_00001

X Ray image

Obturator foramen