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Anterior superior iliac spine

The anterior superior iliac spine (ASIS) is a prominent, anterior projection of the iliac crest of the pelvis. It is one of the most palpable landmarks on the pelvic bone, located at the anterior end of the iliac crest and marking the transition between the lateral and anterior borders of the ilium.

Embryologically, the ASIS develops as part of the ossification centers of the ilium. In adolescents and athletes, the apophysis at the ASIS can be a site of traction injuries due to its muscular and ligamentous attachments.

The ASIS serves as a critical surgical and radiological landmark. It is used to locate the inguinal ligament, femoral artery, and inguinal canal, and to guide incisions in orthopedic and abdominal surgery. It also plays a role in radiographic measurements such as pelvic tilt, acetabular version, and leg length discrepancy.

Attachments

  • Muscular attachment: Sartorius muscle arises from the ASIS and courses obliquely across the thigh.

  • Ligamentous attachment: Inguinal ligament extends from the ASIS to the pubic tubercle, forming the superior border of the femoral triangle.

  • Fascial attachment: Tensor fasciae latae fascia also attaches near the ASIS.

Relations

  • Located superior to the anterior inferior iliac spine (AIIS), separated by the interspinous notch.

  • Marks the lateral boundary of the pelvic brim and upper opening of the inguinal canal.

  • Lies anterior to the iliac ala and contributes to the surface contour of the hip region.

Synonyms

  • ASIS

  • Spina iliaca anterior superior

  • Iliac spine anterior superior

Function

  • Provides origin for sartorius muscle, contributing to hip flexion, abduction, and external rotation.

  • Provides attachment for the inguinal ligament, which stabilizes the anterior abdominal wall and defines the inguinal canal.

  • Serves as a palpable surface landmark for clinical exams and surgical approaches.

  • Important radiographic and orthopedic landmark for pelvic and lower limb alignment studies.

Nerve Supply (related structures)

  • Sartorius muscle: innervated by the femoral nerve (L2–L4)

  • Inguinal ligament region: cutaneous innervation by iliohypogastric and ilioinguinal nerves

Arterial Supply

  • Superficial circumflex iliac artery (branch of femoral artery)

  • Small contributions from iliolumbar artery and superior gluteal artery

Venous Drainage

  • Superficial circumflex iliac vein → femoral vein

  • Additional drainage via iliolumbar and gluteal venous plexuses

MRI Appearance

T1-weighted images:

  • Bone cortex: hypointense (dark)

  • Bone marrow: intermediate signal intensity

  • Clear depiction of cortical outline and surrounding soft tissues

T2-weighted images:

  • Bone cortex: hypointense

  • Bone marrow: intermediate to hyperintense, depending on fat content

  • Acute injury or edema: hyperintense changes in marrow or adjacent soft tissue

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

  • Bone cortex: hypointense

  • Marrow edema or stress reaction: hyperintense signal

  • Highlights enthesopathy, apophyseal injuries, or avulsions at sartorius origin

STIR:

  • Suppresses fat and makes fractures, inflammation, or marrow edema stand out as bright signals

  • Very sensitive for detecting acute avulsion fractures in adolescents

T1 Post-Gadolinium (with fat saturation):

  • Bone cortex: remains hypointense

  • Inflammation, infection, or neoplastic infiltration: enhances brightly

  • Outlines enthesitis, abscesses, or tumors at the ASIS

3D T2-weighted Imaging:

  • Cortex: sharply hypointense

  • Allows multiplanar reconstruction of the ASIS and surrounding structures

  • Useful for surgical planning, especially in pelvic osteotomies or sports injury evaluation

CT Appearance

Non-contrast CT:

  • Bone cortex: hyperdense with crisp margins

  • Bone marrow: lower density compared to cortex

  • Excellent for fractures, apophyseal injuries, cortical irregularities, or bone remodeling

CT Post-Contrast:

  • Bone cortex: unchanged, remains hyperdense

  • Surrounding soft tissues: enhancement highlights inflammation, hematoma, or tumors

  • 3D CT reconstructions used in trauma evaluation, orthopedic surgery planning, and pelvic morphology assessment

CT VRT 3D image

Anterior superior iliac spine 3D IMAGE

CT image

Anterior superior iliac spine CT axial image

MRI image

Anterior superior iliac spine MRI axial anatomy image-img-00000-00000

MRI image

Anterior superior iliac spine spine MRI axial anatomy image-img-00000-00000_00001