Sacrum
Updates to Article Attributes
The sacrum is the penultimate segment of the vertebral column and also forms the posterior part of the bony pelvis. It transmits the total body weight between the lower appendicular skeleton and the axial skeleton.
Gross anatomy
The sacrum is an irregularirregularly-shaped bone, roughly an inverted triangular in shape, with its base superiorly and apex inferiorly. It is curved with an anterior concavity and convex posteriorly.
The sacrum consists of five fused sacral vertebral and costal segments (numbered one-to-five) that form a central sacral body and paired sacral ala, which arise laterally from S1. Superiorly, the anterior lip of the S1 is called the sacral promontory. Posteriorly, the spinous processes are fused to form the median sacral crest.
Through the centre of the sacral body is the triangular-shaped sacral canal, which is the continuation of the lumbar spinal canal. It terminates inferiorly at the sacral hiatus and contains sacral and coccygeal nerve roots, spinal meninges (to the level of S2) and filum terminale. The spinal epidural space extends to the sacral hiatus. First to fourth sacral nerve roots exit the sacrum via four paired anterior and posterior foramen. The fifth sacral nerve root exits via the sacral hiatus.
Articulations
Superiorly, the sacrum articulates with inferior endplate of L5 via the L5/S1 intervertebral disc. Superior articular processes of S1 articulates with the L5 inferior articular facets to form the L5/S1 facet (zygapophyseal) joints. These joints form the lumbosacral articulation.
Inferiorly, the sacrum articulates with the first coccygeal segment at the sacrococcygeal joint.
Laterally, the sacral ala articulate with the ilium to form the sacroiliac joints.
Attachments
Major attachments include:
LigamentsLigamentous
- lumbosacral and iliolumbar ligaments: reinforce lumbosacral articulation
- ligamentum flavum (S1 to L5): closes the spinal/sacral canal posteriorly
- sacroiliac ligaments: reinforce the sacro-iliac joint
- sacrotuberous ligament
- sacrospinous ligament
- superficial sacrococcygeal ligament: closes the sacral hiatus
Musculotendonous
- iliacus muscle: anterosuperiorly
- piriformis muscle: antero-inferiorly
- erector spinae muscle: posteriorly
Relations
- anteriorly: fascia of Waldeyer, superior rectal vessels; peritoneum (S1-S2); rectum (S3-S5); median sacral artery; lymph nodes; piriformis muscle; sacral plexus
Variant anatomy
Related pathology
-<p>The <strong>sacrum</strong> is the penultimate segment of the <a href="/articles/vertebral-column">vertebral column</a> and also forms the posterior part of the <a href="/articles/bony-pelvis">bony pelvis</a>. It transmits the total body weight between the lower appendicular skeleton and the axial skeleton. </p><h4>Gross anatomy</h4><p>The sacrum is an irregular, roughly inverted triangular in shape, with its base superiorly and apex inferiorly. It is curved with an anterior concavity and convex posteriorly.</p><p>The sacrum consists of five fused sacral vertebral and costal segments (numbered one-to-five) that form a central sacral body and paired sacral ala, which arise laterally from S1. Superiorly, the anterior lip of the S1 is called the sacral promontory. Posteriorly, the spinous processes are fused to form the median sacral crest. </p><p>Through the centre of the sacral body is the triangular-shaped sacral canal, which is the continuation of the lumbar spinal canal. It terminates inferiorly at the sacral hiatus and contains sacral and coccygeal nerve roots, <a href="/articles/spinal-meninges">spinal meninges</a> (to the level of S2) and <a href="/articles/filum-terminale">filum terminale</a>. The <a href="/articles/spinal-epidural-space">spinal epidural space</a> extends to the sacral hiatus. First to fourth sacral nerve roots exit the sacrum via four paired anterior and posterior foramen. The fifth sacral nerve root exits via the sacral hiatus. </p><h5>Articulations</h5><p>Superiorly, the sacrum articulates with inferior endplate of <a href="/articles/l5">L5</a> via the L5/S1 <a href="/articles/intervertebral-disc">intervertebral disc</a>. Superior articular processes of S1 articulates with the L5 inferior articular facets to form the L5/S1 facet (zygapophyseal) joints. These joints form the lumbosacral articulation. </p><p>Inferiorly, the sacrum articulates with the first coccygeal segment at the sacrococcygeal joint. </p><p>Laterally, the sacral ala articulate with the <a href="/articles/ilium">ilium</a> to form the <a href="/articles/sacroiliac-joint">sacroiliac joints</a>. </p><h5>Attachments</h5><p>Major attachments include: </p><h6>Ligaments</h6><ul>- +<p>The <strong>sacrum</strong> is the penultimate segment of the <a href="/articles/vertebral-column">vertebral column</a> and also forms the posterior part of the <a href="/articles/bony-pelvis">bony pelvis</a>. It transmits the total body weight between the lower appendicular skeleton and the axial skeleton. </p><h4>Gross anatomy</h4><p>The sacrum is an irregularly-shaped bone, roughly an inverted triangular, with its base superiorly and apex inferiorly. It is curved with an anterior concavity and convex posteriorly.</p><p>The sacrum consists of five fused sacral vertebral and costal segments (numbered one-to-five) that form a central sacral body and paired sacral ala, which arise laterally from S1. Superiorly, the anterior lip of the S1 is called the sacral promontory. Posteriorly, the spinous processes are fused to form the median sacral crest. </p><p>Through the centre of the sacral body is the triangular-shaped sacral canal, which is the continuation of the lumbar spinal canal. It terminates inferiorly at the sacral hiatus and contains sacral and coccygeal nerve roots, <a href="/articles/spinal-meninges">spinal meninges</a> (to the level of S2) and <a href="/articles/filum-terminale">filum terminale</a>. The <a href="/articles/spinal-epidural-space">spinal epidural space</a> extends to the sacral hiatus. First to fourth sacral nerve roots exit the sacrum via four paired anterior and posterior foramen. The fifth sacral nerve root exits via the sacral hiatus. </p><h5>Articulations</h5><p>Superiorly, the sacrum articulates with inferior endplate of <a href="/articles/l5">L5</a> via the L5/S1 <a href="/articles/intervertebral-disc">intervertebral disc</a>. Superior articular processes of S1 articulates with the L5 inferior articular facets to form the L5/S1 facet (zygapophyseal) joints. These joints form the lumbosacral articulation. </p><p>Inferiorly, the sacrum articulates with the first coccygeal segment at the sacrococcygeal joint. </p><p>Laterally, the sacral ala articulate with the <a href="/articles/ilium">ilium</a> to form the <a href="/articles/sacroiliac-joint">sacroiliac joints</a>. </p><h5>Attachments</h5><h6>Ligamentous</h6><ul>
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