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Lesser Sciatic Foramen

foramen ischiadicum minus

The lesser sciatic foramen is the opening formed below the sacrospinous ligament and above the sacrotuberous ligament, through which the obturator internus tendon exits the pelvis to insert at the trochanteric fossa, and through which the pudendal nerve and internal pudendal artery re-enter the perineum after looping around the sacrospinous ligament.

Region: Pelvis & Hip

Clinical Relevance

Clinical Notes

The lesser sciatic foramen is relevant in pudendal neuralgia treatment: pudendal nerve entrapment at the sacrospinous ligament adjacent to the lesser sciatic foramen is the most common entrapment site, accessed by CT-guided injection or surgical decompression of Alcock canal. In hip reconstructive surgery, the obturator internus tendon exiting the lesser sciatic foramen can be identified at the lesser sciatic notch for releases in piriformis syndrome and deep gluteal syndrome.

Pathology

Common Injuries & Conditions

Pudendal Nerve Entrapment at Sacrospinous Ligament

The pudendal nerve looping around the sacrospinous ligament adjacent to the lesser sciatic foramen is the primary entrapment site in pudendal neuralgia, producing perineal pain and dyspareunia worsened by sitting, treated by CT-guided nerve block or surgical decompression of the Alcock canal through the perineum.