AnatomySpine and backSpine

Sacrum and coccyx

Learning objectives

After completing this study unit you will be able to:

Identify the sacrum and the coccyx within the vertebral column.
List the bony landmarks of each of these bones.
Name the joints to which the sacrum and the coccyx contribute and the ligaments associated with them.

Watch video

The sacrum and the coccyx are bony structures located at the caudal end of the vertebral column.

The sacrum is a triangular bone comprising five fused vertebrae. It links to the iliac bones via the sacroiliac joint and plays an important role in stabilizing the hip. Superiorly, it articulates with the last lumbar vertebra (L5) to form the lumbosacral joint. Inferiorly, it articulates with the coccyx to form the sacrococcygeal joint.

The coccyx is the most inferior part of the spine and consists of three to five fused rudimentary coccygeal vertebrae.

Several important ligaments connect the sacrum to the hip bone and help stabilize the sacroiliac joint: sacrospinous ligament and sacrotuberous ligaments as well as anterior, posterior, and interosseous sacroiliac ligaments. The anterior, posterior, and lateral sacrococcygeal ligaments extend between the sacrum and the coccyx and help stabilize the sacrococcygeal joint.

The following video will help you understand the anatomy and bony features of the sacrum and the coccyx and give you an overview of the ligaments associated with these bones.

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Browse atlas

Explore each of the structures you learned about today in the gallery below.

Summary

Key points about the sacrum and coccyx
Sacrum	Structure: Five fused vertebrae Articulations: Lumbar spine via lumbosacral joint Ilium via sacroiliac joint Coccyx via sacrococcygeal joint Landmarks: Base of sacrum Sacral promontory Ala of sacrum Anterior and posterior sacral foramina Apex of sacrum Superior articular process of sacrum Median, intermediate and lateral sacral crests Pelvic surface of sacrum Dorsal surface of sacrum
Coccyx	Structure: Three to five fused vertebrae Articulations: Apex of sacrum via sacrococcygeal joint Landmarks: Apex of coccyx Base of coccyx Coccygeal cornu Transverse processes of coccyx
Ligaments	Sacrospinous and sacrotuberous ligaments Anterior, posterior, and interosseous sacroiliac ligaments Anterior, posterior, and lateral sacrococcygeal ligaments

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