Sacrum & Coccyx

Sacrum & Coccyx: Anatomy & FunctionKey facts about the anatomy of the sacrum and coccyx
~ 3 min

Let us examine the structure of the five sacral vertebrae (vertebrae sacrales). They are fused into a single triangular bone — the sacrum (os sacrum).

Sacral vertebrae (vertebrae sacrales)
Sacral vertebrae (vertebrae sacrales)
Sacrum (os sacrum)
Sacrum (os sacrum)

The following parts are distinguished in the sacrum:

  • Base of the sacrum (basis ossis sacri)

  • Lateral part (pars lateralis)

  • Apex of the sacrum (apex ossis sacri)

Base of the sacrum (basis ossis sacri)
Base of the sacrum (basis ossis sacri)
Lateral part (pars lateralis)
Lateral part (pars lateralis)
Apex of the sacrum (apex ossis sacri)
Apex of the sacrum (apex ossis sacri)

There are also two surfaces — the pelvic surface (facies pelvica) and the dorsal surface (facies dorsalis).

The pelvic surface (facies pelvica)
The pelvic surface (facies pelvica)
The dorsal surface (facies dorsalis)
The dorsal surface (facies dorsalis)

On the pelvic surface, at the junction of the sacrum with the fifth lumbar vertebrae, the so-called promontory (promontorium) comes forward.

Promontory (promontorium)
Promontory (promontorium)

Below you can see the transverse ridges (lineae transversae) — traces of the fusion of the bodies of the sacral vertebrae.

The transverse ridges (lineae transversae)
The transverse ridges (lineae transversae)

And on the dorsal surface on each side is the superior articular process (processus articularis superior), with a corresponding superior articular surface (facies articularis superior) for articulation with the fifth lumbar vertebra.

The superior articular process (processus articularis superior)
The superior articular process (processus articularis superior)

On both surfaces of the sacrum are the anterior sacral foramina (foramina sacralia anteriora), through which the anterior branches of the sacral nerves and blood vessels pass, and the posterior sacral foramina (foramina sacralia posteriora), through which the posterior branches of the sacral nerves and blood vessels pass.

The anterior sacral foramina (foramina sacralia anteriora)
The anterior sacral foramina (foramina sacralia anteriora)
The posterior sacral foramina (foramina sacralia posteriora)
The posterior sacral foramina (foramina sacralia posteriora)

Moreover, the vertebral foramen (foramen vertebrale) of the sacral vertebrae form the sacral canal (canalis sacralis).

The sacral canal (canalis sacralis)
The sacral canal (canalis sacralis)

At the apex, the entrance to this canal is called the sacral hiatus (hiatus sacralis).

The sacral hiatus (hiatus sacralis)
The sacral hiatus (hiatus sacralis)

This hiatus is bounded on each side by the sacral horn (cornu sacrale).

The sacral horn (cornu sacrale)
The sacral horn (cornu sacrale)

On the dorsal surface of the sacrum, there are longitudinal crests, which are the result of the fusion of the vertebral processes:

  • The median sacral crest (crista sacralis mediana) is a trace of the fusion of the spinous processes

    The median sacral crest (crista sacralis mediana)
    The median sacral crest (crista sacralis mediana)
  • The intermediate sacral crest (crista sacralis medialis) is a trace of the fusion of the articular processes

    The intermediate sacral crest (crista sacralis medialis)
    The intermediate sacral crest (crista sacralis medialis)
  • The lateral sacral crest (crista sacralis lateralis) is a trace of fusion of the transverse processes

The lateral sacral crest (crista sacralis lateralis)
The lateral sacral crest (crista sacralis lateralis)

On the lateral parts of the sacrum, there are auricular surfaces (facies auricularis), which articulate with the pelvic bones

The auricular surfaces (facies auricularis)
The auricular surfaces (facies auricularis)

The anterior surface of the lateral part is called the ala of the sacrum (ala ossis sacri), and on the posterior is the sacral tuberosity (tuberositas ossis sacri), where the ligaments are attached.

The ala of the sacrum (ala ossis sacri)
The ala of the sacrum (ala ossis sacri)
The sacral tuberosity (tuberositas ossis sacri)
The sacral tuberosity (tuberositas ossis sacri)

We now come to the structure of the coccygeal vertebrae (vertebrae coccygeae). Their number is not constant (1-5, most often 3).

Like the sacrum, they are fused into a single bone — the coccyx (os coccygis). The coccyx has a base (basis), an apex (apex), as well as a coccygeal cornu (cornu coccygeum), which is used on each side to articulate with the sacrum.

The coccyx (os coccygis)
The coccyx (os coccygis)
Dictionary

Sacrum & Coccyx

sacral vertebrae
vertebrae sacrales
sacrum
os sacrum
base of sacrum
basis ossis sacri
lateral part
pars lateralis
apex of sacrum
apex ossis sacri
pelvis surface
facies pelvica
dorsal surface
facies dorsalis
promontory
promontorium
transverse ridges
lineae transversae
superior articular process
processus articularis superior
superior articular facet
facies articularis superior
anterior sacral foramina
foramina sacralia anteriora
posterior sacral foramina
foramina sacralia posteriora
vertebral foramen
foramen vertebrale
sacral canal
canalis sacralis
sacral hiatus
hiatus sacralis
sacral horn
cornu sacrale
median sacral crest
crista sacralis mediana
intermediate sacral crest
crista sacralis medialis
lateral sacral crest
crista sacralis lateralis
auricular surface
facies auricularis
ala of sacrum
ala ossis sacri
sacral tuberosity
tuberositas ossis sacri
coccygeal vertebrae
vertebrae coccygeae
coccyx
os coccygis
coccygeal cornu
cornu coccygeum
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