The pudendal nerve (S2, S3, S4) exits the pelvis through the greater sciatic foramen below piriformis, then re-enters through the lesser sciatic foramen. It runs in Alcock's canal (the pudendal canal) on the medial surface of which structure?

• A Piriformis muscle
• B Coccygeus muscle
• C Obturator internus muscle ✓
• D Iliococcygeus muscle

Explanation

Alcock's canal (pudendal canal) is a fascial tunnel formed in the obturator fascia on the medial surface of the obturator internus muscle, on the lateral wall of the ischioanal fossa. The pudendal nerve and internal pudendal vessels travel in this canal. Pudendal nerve block anaesthesia is performed near the ischial spine where the nerve is accessible before it enters the canal. Prolonged cycling (cyclist's palsy) can cause pudendal nerve entrapment in 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.