Spine · Irregular bone
Sacrum
The sacrum is a large triangular bone at the base of the spine, formed from five fused vertebrae. It wedges between the two hip bones and transfers the body's weight to the pelvis and legs.
What it is
The sacrum is a single triangular bone made of five vertebrae that fuse during growth. It forms the back of the pelvis.
Where it is
The base of the spine, between the two hip bones, above the tailbone.
What it does
Transfers the weight of the upper body to the pelvis and legs, forms the back wall of the pelvis, and protects the lower nerves.
Connections
Joints and connections
- Sacroiliac joints (with the hip bones)
- Joint with the lowest lumbar vertebra
- Joint with the coccyx
When things go wrong
Common injuries and conditions
- Sacral fracture
- Sacroiliac joint pain (a common cause of lower back and buttock pain)
Education and reference only. This explains the anatomy in plain terms; it is not a diagnosis. A severe injury, a visibly deformed limb, or the inability to move or bear weight needs urgent assessment — call 999 or go to A&E for a serious injury.
Did you know?
An interesting fact
The name "sacrum" comes from the Latin for "sacred bone", possibly because it was used in ancient sacrificial rituals.
Answers
Sacrum: frequently asked questions
What is the sacrum?
The sacrum is a triangular bone at the base of the spine, made of five fused vertebrae. It connects the spine to the pelvis and carries body weight to the legs.
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Related bones
Sources
Where this is drawn from
- NHS — Anatomy and body systems
- Gray's Anatomy for Students (Drake, Vogl, Mitchell)
- TeachMeAnatomy — skeletal system
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