Where do you feel for the ischial spines?
The ischial spines can be palpated at about a finger-length into the vagina, at 4 and 8 o'clock. They are felt as bony prominences. It can be uncomfortable for the woman when you press on the spines.
Why is it important to identify the ischial spines during labour?
1) The station of the fetal head is measured in centimetres above or below the ischial spines:
2) The ischial spines are the landmark for pudendal blocks. The pudendal nerve:
- Arises from the ventral rami of S2, S3 and S4
- Leaves the pelvis through the greater sciatic foramen
- Crosses behind the ischial spine
- Re-enters the pelvis through the lesser sciatic foramen
- Supplies the clitoris, perineum and anus.