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Iliolumbar ligament

The iliolumbar ligament is a strong band of connective tissue that stabilizes the junction between the lumbar spine and pelvis. It extends from the transverse process of the fifth lumbar vertebra to the iliac crest. The ligament reinforces the lumbosacral junction and plays a crucial role in preventing excessive motion between the spine and pelvis. It is clinically relevant in trauma, degenerative changes, and in stabilizing surgical procedures involving the lumbosacral region.

Synonyms

  • Lumbosacral iliac ligament

  • Iliac-lumbar ligament

  • L5 iliac ligament

Origin, Course, and Attachments

  • Origin:

    • Arises from the tip and inferior border of the transverse process of L5 (occasionally also from L4)

  • Course:

    • Passes laterally and slightly posteriorly across the lumbosacral junction

    • Forms a stout fibrous band, often with superior and inferior bands

  • Attachments:

    • Inserts onto the iliac crest and the anterior aspect of the sacroiliac joint capsule

Relations

  • Anteriorly: Iliacus muscle, iliac vessels, lumbosacral trunk

  • Posteriorly: Erector spinae and quadratus lumborum muscles

  • Superiorly: Transverse process of L5

  • Inferiorly: Iliac crest and sacroiliac joint capsule

Function

  • Provides stability to the lumbosacral junction

  • Restricts excessive lateral flexion, rotation, and anterior translation of L5

  • Distributes mechanical load between the lumbar spine and pelvis

  • Acts as a reinforcement of the anterior sacroiliac ligament

Clinical Significance

  • May be strained or injured in lumbosacral instability or trauma

  • Hypertrophy and calcification may occur with degenerative spine disease

  • Can be a source of low back pain (iliolumbar syndrome)

  • Important landmark in spinal and pelvic surgeries

  • Pathology may mimic or contribute to sacroiliac joint disorders

MRI Appearance

T1-weighted images:

  • Appears as a low-signal band extending from L5 to iliac crest

  • Surrounded by bright fat that enhances visualization

T2-weighted images:

  • Ligament shows low signal intensity

  • Pathology (strain, degeneration) may cause focal areas of higher signal

STIR (Short Tau Inversion Recovery):

  • Normal ligament remains dark

  • Inflammation, edema, or injury appears as bright hyperintensity

T1 Fat-Sat Post-Contrast:

  • Normal ligament shows no significant enhancement

  • Pathology (enthesitis, inflammation, tumor infiltration) may show focal enhancement

3D T2 SPACE / CISS:

  • Ligament appears as a dark linear band

  • Surrounded by bright CSF and fat, improving contrast with adjacent structures

  • Useful for distinguishing ligament from nearby nerve roots or vessels

CT Appearance

Non-Contrast CT:

  • Appears as a soft tissue band between L5 transverse process and iliac crest

  • Chronic degeneration may show calcification within ligament fibers

Post-Contrast CT:

  • Ligament itself does not enhance

  • Pathologic changes may appear as soft tissue thickening or enhancement of adjacent tissues

  • Calcification or ossification visible as high-density foci

MRI image

Iliolumbar ligament mri axial image

MRI image

Iliolumbar ligament mri coronal image

MRI image

Iliolumbar ligament

CT image

Iliolumbar ligament ct coronal anatomy image-img-00000-00000