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Sacrotuberous ligament

The sacrotuberous ligament is a strong, fibrous band of the pelvis that extends from the sacrum to the ischial tuberosity. It plays an essential role in stabilizing the sacroiliac joint, converting the sciatic notches into foramina, and transmitting mechanical forces between the trunk and lower limb. The ligament is also important as an anatomical landmark for pelvic surgeons and in imaging of posterior pelvic pain syndromes.

Synonyms

  • Posterior sacrosciatic ligament

  • Sacral tuberosity ligament

Attachments and Course

  • Proximal attachments: Posterior superior iliac spine (PSIS), posterior inferior iliac spine (PIIS), lateral margins of sacrum and coccyx

  • Course: Fibers pass obliquely downward and laterally, forming a broad, flat band

  • Distal attachment: Medial margin of the ischial tuberosity

Relations

  • Anteriorly: Sacrospinous ligament, coccygeus muscle, gluteus maximus (deep fibers)

  • Posteriorly: Gluteus maximus muscle, skin of gluteal region

  • Laterally: Sciatic foramina and structures passing through them (sciatic nerve, pudendal nerve, internal pudendal vessels)

  • Medially: Sacrum and coccyx

Function

  • Stabilizes the sacrum by resisting forward tilting and rotation

  • Helps form the greater and lesser sciatic foramina together with the sacrospinous ligament

  • Transmits forces between sacrum, pelvis, and lower limb

  • Provides attachment for part of the gluteus maximus and piriformis fascia

Clinical Significance

  • Involved in pelvic instability and sacroiliac joint dysfunction

  • Can be a source of posterior pelvic and gluteal pain due to ligament strain or enthesopathy

  • Acts as a surgical landmark in procedures involving the pudendal nerve or pelvic outlet

  • May calcify or thicken in chronic stress, visible on imaging

MRI Appearance

T1-weighted images:

  • Ligament appears as a dark, low-signal band from sacrum to ischial tuberosity

  • Surrounded by bright fat planes that enhance visualization

T2-weighted images:

  • Ligament remains low signal intensity

  • Partial tears, inflammation, or enthesopathy may show focal bright signal

STIR (Short Tau Inversion Recovery):

  • Normal ligament remains dark

  • Strain, edema, or inflammation appear as bright hyperintensity

T1 Fat-Sat Post-Contrast:

  • Normal ligament shows minimal to no enhancement

  • Inflammatory or injured ligament shows focal enhancement at attachment sites

CT Appearance

Non-Contrast CT:

  • Ligament is seen as a soft tissue density band extending from sacrum to ischial tuberosity

  • Calcification or ossification may be present in chronic cases

Post-Contrast CT:

  • Normal ligament shows little to no enhancement

  • Adjacent soft tissue inflammation, abscess, or tumor infiltration may enhance and alter its margins

MRI image

sacrotuberous ligament MRI axial image

CT image

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MRI image

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MRI image

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