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Topic

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Sacrospinous ligament

The sacrospinous ligament is a short, triangular fibrous structure in the pelvis. It plays a crucial role in stabilizing the sacrum and forming the boundaries of the greater and lesser sciatic foramina. Along with the sacrotuberous ligament, it resists rotational forces on the sacrum and provides anchorage for pelvic floor structures. It is an important landmark in pelvic surgery and is involved in procedures for prolapse repair.

Synonyms

  • Small sacrosciatic ligament

  • Sacral spinous ligament

Attachments and Course

  • Attachments:

    • Originates from the lateral margin of the sacrum and coccyx

    • Extends laterally to attach onto the ischial spine

  • Course:

    • Forms a triangular sheet of dense fibrous tissue

    • Oriented horizontally and anterior to the sacrotuberous ligament

    • Divides the greater sciatic notch into the greater sciatic foramen (superiorly) and the lesser sciatic foramen (inferiorly)

Relations

  • Anteriorly: Coccygeus muscle and pelvic floor structures

  • Posteriorly: Sacrotuberous ligament

  • Superiorly: Piriformis muscle and greater sciatic foramen contents

  • Inferiorly: Lesser sciatic foramen, obturator internus tendon

  • Laterally: Ischial spine and ischium

Function

  • Stabilizes the sacrum by preventing its forward rotation relative to the pelvis

  • Helps maintain the integrity of the sacroiliac joint

  • Forms the boundary of the greater and lesser sciatic foramina, guiding pelvic neurovascular structures

  • Provides secondary support to the pelvic floor

Clinical Significance

  • Important landmark in pelvic surgery, especially in sacrospinous ligament fixation for pelvic organ prolapse

  • May be involved in pelvic pain syndromes

  • Close relationship with pudendal nerve and internal pudendal vessels, making it relevant in nerve entrapment and surgical complications

  • Can be thickened or injured in trauma, visible on imaging

MRI Appearance

T1-weighted images:

  • Appears as a thin, low-signal band between sacrum/coccyx and ischial spine

  • Surrounded by higher signal fat planes for contrast

T2-weighted images:

  • Remains low signal intensity

  • Injury, edema, or inflammation appears as focal bright areas

STIR (Short Tau Inversion Recovery):

  • Normally dark

  • Injury, strain, or inflammatory change appears as bright hyperintensity

T1 Fat-Sat Post-Contrast:

  • No significant enhancement in the normal ligament

  • Pathology (enthesitis, inflammation, tumor infiltration) may enhance focally

CT Appearance

Non-Contrast CT:

  • Appears as a thin, soft tissue density band extending from sacrum/coccyx to ischial spine

  • Calcifications or ossification may be seen in chronic changes

Post-Contrast CT:

  • Ligament itself does not enhance significantly

  • Surrounding enhancement may be present in cases of inflammation, abscess, or neoplastic invasion

MRI image

Sacrospinous ligament MRI axial image

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Sacrospinous ligament sag mri image

CT image

Sacrospinous ligament CT axial anatomy image

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MRI image

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