The pudendal nerve provides somatic innervation to the perineum and is blocked for obstetric analgesia. Through which structure must the needle pass to reach the pudendal nerve at the level of the ischial spine during a transvaginal block?

• A Sacrotuberous ligament
• B Piriformis muscle
• C Obturator internus fascia
• D Sacrospinous ligament ✓

Explanation

The pudendal nerve leaves the pelvis through the greater sciatic foramen below piriformis, winds around the ischial spine and sacrospinous ligament, then re-enters the perineum through the lesser sciatic foramen. In a transvaginal pudendal nerve block, the needle is directed to the ischial spine and penetrates the sacrospinous ligament to reach the nerve in the pudendal (Alcock's) canal. The sacrotuberous ligament is more posterior; piriformis lies superior to the nerve; obturator internus fascia forms the roof of Alcock's canal.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.