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Topic

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Ischial spine

The ischial spine is a thin, triangular, pointed bony projection extending posteriorly from the ischium, situated between the greater and lesser sciatic notches of the pelvis. It projects medially into the pelvic cavity and serves as a crucial anatomical and surgical landmark.

Embryologically, it develops from the ossification centers of the ischium, fusing into the pelvic ring. The ischial spine is important for pelvic stability, ligamentous attachment, and as a reference point in obstetrics and pelvic surgery.

Attachments

  • Sacrospinous ligament (extends from ischial spine to sacrum, dividing greater and lesser sciatic foramina)

  • Coccygeus muscle attaches partly to sacrospinous ligament at this level

  • Related structures: obturator internus muscle passes laterally, while pudendal nerve and internal pudendal vessels cross nearby

Relations

  • Lies between the greater sciatic notch (superiorly) and the lesser sciatic notch (inferiorly)

  • Close to the pudendal nerve, internal pudendal vessels, and sciatic nerve as they pass through sciatic foramina

  • Palpable during vaginal examination, important in obstetric assessment of pelvic dimensions

Synonyms

  • Spina ischiadica

  • Pelvic ischial projection

Function

  • Provides attachment for sacrospinous ligament, stabilizing pelvic outlet

  • Serves as an obstetric landmark for determining fetal head station during labor

  • Acts as a radiological and surgical reference point for pelvic surgery and nerve blocks

Nerve Supply (related region)

  • Pudendal nerve (passes around ischial spine)

  • Nerve to obturator internus (nearby)

Arterial Supply

  • Branches from the inferior gluteal artery and internal pudendal artery supply surrounding ligaments and soft tissues

Venous Drainage

  • Corresponding tributaries drain into the internal pudendal vein and inferior gluteal vein

MRI Appearance

T1-weighted images:

  • Bone cortex: hypointense (black)

  • Bone marrow: intermediate signal

  • Sacrospinous ligament attachment: seen as hypointense linear structure

T2-weighted images:

  • Bone cortex: hypointense

  • Marrow: intermediate to hyperintense depending on fat content

  • Surrounding ligaments: remain hypointense

  • Useful for detecting inflammatory or neoplastic changes

PD Fat-Saturated (Proton Density with Fat Suppression):

  • Bone cortex: hypointense

  • Marrow edema or stress reaction: bright hyperintense

  • Useful for sacrospinous enthesopathy or apophyseal stress injury

STIR:

  • Bone cortex: hypointense

  • Bone marrow edema or acute trauma: hyperintense

  • Excellent for detecting stress fractures or early sacrospinous ligament injury

T1 Post-Gadolinium (with fat saturation):

  • Bone cortex: remains hypointense

  • Inflammatory tissue, tumors, or infection: enhance brightly

  • Useful in evaluating abscesses, osteomyelitis, or soft tissue tumors at ischial spine

3D T2-weighted Imaging:

  • Cortex: dark hypointense outline

  • High-resolution multiplanar reconstructions of ischial spine and sciatic foramina anatomy

  • Critical for surgical navigation, pelvic nerve blocks, and tumor mapping

CT Appearance

Non-contrast CT:

  • Bone cortex: hyperdense and sharply defined

  • Bone marrow: relatively hypodense compared to cortex

  • Excellent for identifying fractures, cortical irregularities, or pelvic morphology

CT Post-Contrast:

  • Bone cortex: unchanged (hyperdense)

  • Surrounding soft tissues: enhancement demonstrates inflammation, abscess, or neoplastic involvement

  • 3D CT reconstructions useful in pelvic fracture evaluation and surgical planning

Clinical Significance

  • Obstetrics: palpable landmark to assess fetal head station (+/– relative to ischial spines).

  • Pelvic surgery: landmark for pudendal nerve blocks and sacrospinous ligament fixation.

  • Trauma: fracture of ischial spine may occur with pelvic ring injuries.

  • Pathology: site of enthesopathy, tumors, or spread of pelvic infections.

CT VRT 3D image

Ischial spine 3D CT VRT anatomy image

CT image

Ischial spine CT axial image

MRI image

Ischial spine MRI axial anatomy image