The greater and lesser sciatic foramina are two openings in the posterior aspect of the pelvis.
The greater sciatic foramen is larger and is separated from the lesser sciatic foramen by the sacrospinous ligament.
In this article, we shall look at the anatomy of the greater sciatic foramen and lesser sciatic foramen – their borders and contents.
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Greater Sciatic Foramen
The greater sciatic foramen provides a passageway for structures to pass from the pelvis into the gluteal region.
Borders
The greater sciatic foramen is bordered by:
- Superior – anterior sacroiliac ligament
- Posteromedial – sacrotuberous ligament
- Anterolateral – greater sciatic notch of the ilium
- Inferior – sacrospinous ligament and ischial spine
Contents
The greater sciatic foramen is divided into two parts by the presence of the piriformis muscle – the suprapiriform and infrapiriform foramina.
- Suprapiriform foramen:
- Superior gluteal artery and vein
- Superior gluteal nerve
- Infrapiriform foramen:
- Sciatic nerve
- Pudendal nerve
- Inferior gluteal artery and vein
- Inferior gluteal nerve
- Posterior femoral cutaneous nerve
- Nerve to obturator internus
- Nerve to quadratus femoris
Fig 2
The piriformis divides the greater sciatic foramen into two – the supra- and infrapiriform foramina.
Lesser Sciatic Foramen
The lesser sciatic foramen provides a communication between the perineum of the pelvis and the gluteal region. It lies inferiorly to the pelvic floor.
Borders
The lesser sciatic foramen is bordered by:
- Superior – sacrospinous ligament and ischial spine
- Anterior – ischial spine, lesser sciatic notch and ischial tuberosity
- Posterior – sacrotuberous ligament
Contents
The following structures pass through the lesser sciatic foramen:
- Internal pudendal artery and vein
- Pudendal nerve (note the pudendal nerve first leaves the pelvis via the greater sciatic foramen, and then re-enters via the lesser sciatic foramen)
- Obturator internus tendon
- Nerve to obturator internus
Fig 3
The pudendal nerve first leaves the pelvis via the greater sciatic foramen, and then re-enters via the lesser sciatic foramen