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Ischial Spine

spina ischiadica

The ischial spine is the pointed projection from the posterior ischium between the greater and lesser sciatic notches. It serves as the attachment site for the sacrospinous ligament (converting the greater and lesser sciatic notches into foramina) and the coccygeus muscle. The pudendal nerve and internal pudendal artery cross over the ischial spine as they pass from the greater to the lesser sciatic foramen.

Anatomical Data

Structure & Landmarks

Articulations	Sacrospinous ligament medially Coccygeus muscle
Landmarks	Palpable on rectal or vaginal examination as a sharp bony prominence Level approximately 10 cm above the perineum in the female pelvis Fetal station reference point during labour progress assessment
Ossification	Ossifies as part of the ischium, contributing to the posterior pelvic ring.

Clinical Relevance

Clinical Notes

The ischial spines are the reference points for fetal station in labour. Station 0 is when the fetal presenting part reaches the level of the ischial spines, with station expressed in centimetres above (negative) or below (positive) this reference. Pudendal nerve block is performed by directing a needle transvaginally to the sacrospinous ligament just posterior to the ischial spine. Sacrospinous fixation for vaginal vault prolapse places sutures through the sacrospinous ligament immediately lateral to the ischial spine.

Pathology

Common Injuries & Conditions

Pudendal Nerve Entrapment

The pudendal nerve crosses the sacrospinous ligament at the ischial spine and can be compressed there, causing perineal pain worse on sitting.

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