CT Lower Limb Anatomy – Normal Labeled CT Axial, Coronal, Sagittal Cross-Sectional Images

Topic

Anterior inferior iliac spine

The anterior inferior iliac spine (AIIS) is a bony prominence of the ilium, located just inferior to the anterior superior iliac spine (ASIS), separated by the interspinous groove. It projects anteriorly from the ilium above the acetabulum and serves as an important attachment site for muscles and ligaments.

The AIIS provides the proximal origin for the direct (straight) head of the rectus femoris muscle and attachment for the iliofemoral ligament, one of the strongest ligaments in the body, which stabilizes the hip joint. The reflected (indirect) head of rectus femoris arises from the acetabular rim, in close relation to the AIIS.

It is a critical surgical and imaging landmark. Avulsion fractures of the AIIS are common in adolescents and athletes due to strong traction forces of the rectus femoris. Overuse or abnormal morphology of the AIIS may contribute to subspine impingement, a recognized subtype of femoroacetabular impingement (FAI).

Attachments

Muscle attachment: Direct head of rectus femoris
Ligament attachment: Iliofemoral ligament (superior band)
Capsular attachment: Part of the anterior hip capsule

Relations

Lies superior to the acetabular rim and anterior to the hip joint
Located inferior to the ASIS, separated by the interspinous groove
Closely related to rectus femoris tendon and anterior joint capsule

Synonyms

AIIS
Spina iliaca anterior inferior

Function

Provides origin for rectus femoris (straight head), aiding hip flexion and knee extension
Serves as an attachment site for iliofemoral ligament, contributing to hip stability
Acts as a landmark in imaging and surgical approaches to the hip and pelvis

Nerve Supply (related structures)

Rectus femoris muscle: innervated by femoral nerve (L2–L4)

Arterial Supply

Ascending branch of lateral circumflex femoral artery (primary supply to rectus femoris origin)
Contributions from superior gluteal artery and iliolumbar artery

Venous Drainage

Lateral circumflex femoral vein → femoral vein
Anastomotic drainage via iliac and gluteal venous networks

MRI Appearance

T1-weighted images:

Bone cortex: hypointense
Marrow: intermediate signal
Identifies avulsion fragments or marrow infiltration

T2-weighted images:

Bone cortex: hypointense
Marrow: intermediate to hyperintense if edema is present
Useful for detecting stress changes, avulsions, or cortical irregularity

PD Fat-Saturated (Proton Density FS):

Bone cortex: hypointense
Marrow edema, tendon pathology, or avulsions: hyperintense
Very sensitive for rectus femoris origin injuries

STIR:

Highlights acute avulsion injuries, bone marrow edema, or enthesitis
Suppresses fat for clear visualization of inflammatory changes

T1 Post-Gadolinium (with fat saturation):

Bone cortex: remains hypointense
Inflammation, tumors, or infection: abnormal enhancement
Useful for evaluating enthesitis, neoplasms, or post-surgical changes

3D T2-weighted Imaging:

Bone cortex: sharply hypointense
Provides multiplanar reconstruction of AIIS morphology
Essential in FAI evaluation and preoperative planning for hip surgery

CT Appearance

Non-contrast CT:

Bone cortex: hyperdense and sharply outlined
Marrow cavity: hypodense relative to cortex
Gold standard for detecting fractures, avulsion injuries, and cortical morphology (subspine prominence)

CT Post-Contrast:

Bone cortex: unchanged
Surrounding soft tissues: enhancement indicates inflammation, hematoma, or tumor
3D CT reconstructions valuable in orthopedic planning and pelvic trauma evaluation

CT VRT 3D image