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Sacrum and coccyx

Learning objectives

After completing this study unit you will be able to:

  1. Identify the sacrum and the coccyx within the vertebral column.
  2. List the bony landmarks of each of these bones.
  3. 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 sacral vertebrae, S1-S5. It articulates with the iliac components of the hip bones via the sacroiliac joint, therefore contributing to the pelvic girdle and playing an important role in stabilization of the pelvis. Superiorly, it articulates with the inferiormost 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.

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.


Key points about the sacrum
Structure Five fused sacral vertebrae (S1-S5)
Parts Dorsal surface: median crest, intermediate crests, lateral crests, four pairs of posterior sacral foramina, sacral horns
Pelvic surface: Transverse ridges, sacral promontory, four pairs of anterior sacral foramina
Lateral (auricular) surface: Articulates with ilium
Base: Articulates with L5
Apex: Articulates with coccyx
Key points about the coccyx
Structure 3-5 fused coccygeal vertebrae
Parts Apex, base, coccygeal horns
Key points about the joints of sacrum and coccyx
Joints Lumbosacral joint (symphysis):
Anterior intervertebral joint
Zygapophyseal joints

Sacroiliac joint
Synovial articulation between auricular surface of sacrum and auricular surface of ilium
Syndesmosis between sacral tuberosity and iliac tuberosity

Sacrococcygeal joint
Apex of sacrum and base of coccyx via intervertebral disc
Sacrococcygeal zygapophyseal joint

Intercoccygeal joints
Cartilaginous or ossified joints between adjacent coccygeal vertebrae
Ligaments Lumbosacral symphysis:
Iliolumbar ligaments
Lumbosacral ligaments

Sacroiliac joints
Anterior sacroiliac ligament
Interosseous sacroiliac ligament
Posterior sacroiliac ligament

Sacrococcygeal joints
Superficial posterior sacrococcygeal ligament
Deep posterior sacrococcygeal ligament
Anterior sacrococcygeal ligament
Lateral sacrococcygeal ligament
Sacrotuberous ligament
Sacrospinous ligament

Intercoccygeal joints
Supraspinous ligament (sacral part)
Anterior longitudinal ligament (sacral part)
Anterior sacrococcygeal ligament
Lateral sacrococcygeal ligament

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