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Robotic Spine Universe

Structures · Vertebrae

Sacrum

The sacrum: the fused sacral vertebrae, joining the column to the pelvis.

Show in the 3D spineSee what it connects to in the body

At a glance

Level system
Sacrum (vertebral)
Fused pieces
5Betts et al. 2022, §7.3
Canal, front to back × side to side
17.9 × 38.3 mmMeasured on one model: the Visible Human male, imaged as a supine cadaver. Not a normal range
L5 nerve
The L5 nerve exits between the L5 vertebra and the sacrum, below the L5 vertebra.Betts et al. 2022, §13.4
S1 nerve
The S1 nerve leaves through the S1 sacral foramina.Betts et al. 2022, §13.4
S2 nerve
The S2 nerve leaves through the S2 sacral foramina.Betts et al. 2022, §13.4
S3 nerve
The S3 nerve leaves through the S3 sacral foramina.Betts et al. 2022, §13.4
S4 nerve
The S4 nerve leaves through the S4 sacral foramina.Betts et al. 2022, §13.4
S5 nerve
The S5 nerve leaves through the sacral hiatus.Betts et al. 2022, §13.4
Co1 nerve
The Co1 nerve leaves through the sacral hiatus.Betts et al. 2022, §13.4

What the sources say

“It is formed by the fusion of five sacral vertebrae, a process that does not begin until after the age of 20.” Betts et al. 2022, §7.3
“Passing inferiorly through the sacrum is a bony tunnel called the sacral canal , which terminates at the sacral hiatus near the inferior tip of the sacrum.” Betts et al. 2022, §7.3

Connections to the rest of the body

Read more

  • Sagittal alignment

    How the spine's side-view curves and the pelvis work together to keep the trunk balanced over the hips. Pelvic incidence, tilt and slope, the C7 plumb line, and how the body compensates when alignment is lost.

  • The sacrum and coccyx

    The fused bones at the base of the column. The sacrum carries the weight of the trunk into the pelvis and lets the sacral nerves out through its foramina; the coccyx is the tailbone.

  • The vertebral column

    The flexible stack of bones that carries the head and trunk, protects the spinal cord and lets the back move. Its five regions, its four curves and the parts every vertebra shares.

For learning only. Levels and sizes vary between people; nothing here describes a particular person or gives medical advice. Sources: Betts et al. 2022, §7.3; Betts et al. 2022, §13.4; Betts et al. 2022, §11.6.