What is the sacrum and what is its function?

The sacrum is a large, triangular bone formed by the fusion of five sacral vertebrae. It serves as the posterior part of the bony pelvis, supporting the vertebral column and transmitting body weight to the pelvic girdle.

How does the sacrum articulate with other bones?

The sacrum articulates with the hip bones at the sacroiliac joints via its auricular surfaces. It also connects to the L5 vertebra at the lumbosacral joint and to the coccyx at the sacrococcygeal joint.

What are the key features of the sacral surfaces?

The sacrum has three main surfaces: Pelvic surface (concave, with transverse ridges and anterior foramina), dorsal surface (convex and rough, with vertical crests and dorsal foramina), and lateral surfaces (including the auricular surface for articulation with the ilium).

What structures are found within the sacral canal?

The sacral canal contains the cauda equina, filum terminale, spinal meninges, and lateral sacral vessels. It opens at the sacral hiatus, where the S5 and coccygeal nerves and filum terminale emerge.

What muscles and ligaments attach to the sacrum?

Key attachments include the piriformis muscle (arises from S2–S4 bodies), erector spinae and multifidus muscles (originate on the dorsal surface), and ligaments like the sacrotuberous and sacrospinous near the inferolateral angle.

How does the sacrum differ between males and females?

Sex differences include the base (broader body in males, narrower in females), pelvic surface (C-shaped in males, J-shaped in females), and auricular surface (larger and less oblique in males).

What are sacralization and lumbarization?

Sacralization is the fusion of L5 or C1 with the sacrum, potentially increasing sacral foramina. Lumbarization occurs when S1 separates and fuses with L5, reducing sacral foramina to three pairs.

Sacrum – Anatomy, Foramina & Articulations

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