Sacral Hiatus S5 — FRCA Primary MCQ
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Correct answer: B — S5
The sacral hiatus is formed by the failure of fusion of the S5 (and sometimes S4) laminae. It is covered by the sacrococcygeal ligament. The sacral cornua (two bony prominences) are palpable landmarks flanking the hiatus. The dural sac terminates at approximately S2 so caudal injection below this is epidural not subarachnoid.
Reference: RCoA 2021 Primary FRCA Curriculum