The sacrum
Sacrum · os sacrum
A triangular bone at the base of your spine, made of five vertebrae fused into one.
What it does
The sacrum is wedged between your two hip bones like a keystone in an arch. It passes the weight of your upper body into the pelvis and on to the legs. Openings along it let nerves out to the pelvis and legs, including the roots of the sciatic nerve.
Surprising fact
The name comes from the Latin os sacrum, "sacred bone", possibly because ancient people believed it resisted decay or was used in sacrifices.
Why it matters
The joints where the sacrum meets the hips can become a source of lower back and buttock pain, especially during pregnancy, when hormones loosen the ligaments that normally hold them tight.
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Open in the 3D atlas · Suggest a correction · Not medical advice.
3D models: Z-Anatomy & BodyParts3D (CC BY-SA 4.0 / 2.1 JP). Card text CC BY 4.0.