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Ala of sacrum

The ala of the sacrum (sacral wing) refers to the broad, wing-like lateral projections of the sacrum formed by the fused transverse processes of the upper sacral vertebrae. Each ala extends laterally from the first sacral segment (S1) and articulates with the ilium at the sacroiliac joint.

The sacral ala provides a transitional surface between the spinal column and the pelvic bones, playing a key role in weight transmission from the axial skeleton to the lower limbs. It is covered by the iliacus and psoas major muscles, and it serves as an important anatomical landmark for spinal interventions and sacroiliac joint imaging.

Clinically, the ala is significant in sacroiliac joint dysfunction, fractures, tumor spread, infection, and trauma. In orthopedic surgery and interventional radiology, it is a reference point for sacroplasty, iliosacral screw fixation, and sacral nerve procedures.

Synonyms

  • Sacral wing

  • Ala sacralis

  • Lateral part of sacrum

Function

  • Transmits weight of the body from the vertebral column to the pelvic girdle

  • Forms part of the sacroiliac joint articulation with the ilium

  • Provides attachment points for ligaments and muscles of the pelvis

  • Serves as a radiological and surgical landmark in sacral procedures

Nerve Supply

  • No direct muscular innervation; nearby structures receive innervation from sacral plexus (L4–S4)

  • Clinical importance in proximity to sacral nerve roots in sacral interventions

Arterial Supply

  • Branches of the lateral sacral arteries (from the internal iliac artery)

  • Small contributions from the iliolumbar artery

Venous Drainage

  • Venous blood drains into the lateral sacral veins, which connect with the internal vertebral venous plexus and internal iliac vein

MRI Appearance

T1-weighted images:

  • Normal ala shows low signal cortex with intermediate bone marrow signal

  • Surrounded by hyperintense pelvic fat planes aiding contrast

T2-weighted images:

  • Cortical bone appears hypointense

  • Bone marrow appears intermediate signal, with hyperintense signal in cases of edema or pathology

STIR:

  • Suppresses fat, showing bone marrow edema, fractures, or tumor infiltration as hyperintense signals

  • Sensitive for sacral stress fractures and metastatic disease

T1 Fat-Saturated (Pre-contrast):

  • Shows intermediate marrow signal with fat suppressed, improving detection of abnormal marrow changes

T1 Fat-Saturated Post-Contrast (Gadolinium):

  • Normal marrow enhances mildly and homogeneously

  • Pathology (tumors, infection, inflammatory processes) enhances more intensely and heterogeneously

MRI Non-Contrast 3D Imaging:

  • Provides detailed reconstructions of sacral ala morphology and sacroiliac joint relationships

  • Useful for surgical navigation and congenital anomaly evaluation

CT Appearance

CT Pre-Contrast:

  • Ala visualized as dense cortical bone with trabecular pattern

  • Excellent for detecting fractures, sclerosis, and bone lesions

CT Post-Contrast:

  • Bony architecture does not enhance, but surrounding soft tissue or tumor extension may enhance

  • Useful for assessing infection, tumor invasion, or postoperative changes

  • 3D reconstructions demonstrate sacroiliac joint articulation and ala morphology

CT images

ala of sacrum ct axial image

CT VRT 3D image

ala of sacrum ct 3d image

MRI image

ala of sacrum MRI axial anatomy image -img-00000-00000