An anaesthetist performs a caudal epidural block in a child for postoperative analgesia after herniotomy. The needle is advanced through the sacrococcygeal membrane into the sacral canal. The sacral hiatus, the entry point for this block, is best identified on the surface by palpating which structures?

• A Posterior superior iliac spines
• B Ischial tuberosities
• C Iliac crests
• D Sacral cornua flanking the hiatus ✓

Explanation

The sacral hiatus is formed by failure of fusion of the laminae of the fifth sacral vertebra and is flanked on each side by the sacral cornua, the downward projections of the S4 articular processes. Palpating these two small bony prominences in the natal cleft identifies the hiatus, which is closed by the sacrococcygeal membrane. The posterior superior iliac spines mark S2, the level at which the dural sac ends, and the iliac crests mark the L4 level used for lumbar puncture.

Reference: Snell's Clinical Anatomy by Regions, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.