Sacrum
Sacrum | |
---|---|
Details | |
Pronunciation | (/ˈsækrəm/ or /ˈseɪkrəm/ |
Location | Base of the vertebral column |
Identifiers | |
Latin | os sacrum |
MeSH | D012447 |
TA98 | A02.2.05.001 |
TA2 | 1071 |
FMA | 16202 |
Anatomical terms of bone |
The sacrum (pl.: sacra or sacrums[1]), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1–S5) between ages 18 and 30.[2]
The sacrum situates at the upper, back part of the pelvic cavity, between the two wings of the pelvis. It forms joints with four other bones. The two projections at the sides of the sacrum are called the alae (wings), and articulate with the ilium at the L-shaped sacroiliac joints. The upper part of the sacrum connects with the last lumbar vertebra (L5), and its lower part with the coccyx (tailbone) via the sacral and coccygeal cornua.
The sacrum has three different surfaces which are shaped to accommodate surrounding pelvic structures. Overall, it is
In all other
The Stegosaurus dinosaur had a greatly enlarged neural canal in the sacrum, characterized as a "posterior brain case".[4]
Structure
The sacrum is a complex structure providing support for the spine and accommodation for the spinal nerves. It also articulates with the hip bones. The sacrum has a base, an apex, and three surfaces – a pelvic, dorsal and a lateral surface. The base of the sacrum, which is broad and expanded, is directed upward and forward. On either side of the base is a large projection known as an ala of sacrum and these alae (wings) articulate with the sacroiliac joints. The alae support the psoas major muscles and the lumbosacral trunk which connects the lumbar plexus with the sacral plexus. In the articulated pelvis, the alae are continuous with the iliac fossa. Each ala is slightly concave from side to side, and convex from the back and gives attachment to a few of the fibers of the iliacus muscle. The posterior quarter of the ala represents the transverse process, and its anterior three-quarters the costal process of the first sacral segment. Each ala also serves as part of the border of the pelvic brim. The alae also form the base of the lumbosacral triangle. The iliolumbar ligament and lumbosacral ligaments are attached to the ala.
In the middle of the base is a large oval articular surface, the upper surface of the body of the first sacral vertebra, which is connected with the under surface of the body of the last
The apex is directed downward and presents an oval facet for articulation with the
Promontory
The sacral promontory marks part of the border of the pelvic inlet, and comprises the iliopectineal line and the linea terminalis.[5] The sacral promontory articulates with the last lumbar vertebra to form the sacrovertebral angle, an angle of 30 degrees from the horizontal plane that provides a useful marker for a sling implant procedure.
Surfaces
The pelvic surface of the sacrum is concave from the top, and curved slightly from side to side. Its middle part is crossed by four transverse ridges, which correspond to the original planes of separation between the five sacral vertebrae. The body of the first segment is large and has the form of a lumbar vertebra; the bodies of the next bones get progressively smaller, are flattened from the back, and curved to shape themselves to the sacrum, being concave in front and convex behind. At each end of the transverse ridges, are the four anterior sacral foramina, diminishing in size in line with the smaller vertebral bodies. The foramina give exit to the anterior divisions of the
The dorsal surface of the sacrum is convex and narrower than the pelvic surface. In the middle line is the median sacral crest, surmounted by three or four
On the lateral aspect of the sacral groove is a linear series of tubercles produced by the fusion of the articular processes which together form the indistinct medial sacral crest. The articular processes of the first sacral vertebra are large and oval-shaped. Their facets are concave from side to side, face to the back and middle, and articulate with the facets on the inferior processes of the fifth lumbar vertebra.
The tubercles of the inferior articular processes of the fifth sacral vertebra, known as the sacral cornua, are projected downward and are connected to the cornua of the coccyx. At the side of the articular processes are the four posterior sacral foramina; they are smaller in size and less regular in form than those at the front, and transmit the posterior divisions of the sacral nerves. On the side of the posterior sacral foramina is a series of tubercles, the transverse processes of the sacral vertebrae, and these form the lateral sacral crest. The transverse tubercles of the first sacral vertebra are large and very distinct; they, together with the transverse tubercles of the second vertebra, give attachment to the horizontal parts of the posterior sacroiliac ligaments; those of the third vertebra give attachment to the oblique fasciculi of the posterior sacroiliac ligaments; and those of the fourth and fifth to the sacrotuberous ligaments.
The lateral surface of the sacrum is broad above, but narrows into a thin edge below. The upper half presents in front an ear-shaped surface, the auricular surface, covered with cartilage in the immature state, for articulation with the ilium. Behind it is a rough surface, the sacral tuberosity, on which are three deep and uneven impressions, for the attachment of the posterior sacroiliac ligament. The lower half is thin, and ends in a projection called the inferior lateral angle. Medial to this angle is a notch, which is converted into a foramen by the transverse process of the first piece of the coccyx, and this transmits the anterior division of the fifth sacral nerve. The thin lower half of the lateral surface gives attachment to the
Articulations
The sacrum articulates with four bones:
- the last lumbar vertebraabove
- the coccyx (tailbone) below
- the ilium portion of the hip bone on either side
Rotation of the sacrum superiorly and anteriorly whilst the coccyx moves posteriorly relative to the ilium is sometimes called "nutation" (from the Latin term nutatio which means "nodding") and the reverse, postero-inferior motion of the sacrum relative to the ilium whilst the coccyx moves anteriorly, "counter-nutation".[6] In upright vertebrates, the sacrum is capable of slight independent movement along the sagittal plane. On bending backward the top (base) of the sacrum moves forward relative to the ilium; on bending forward the top moves back.[7]
The sacrum refers to all of the parts combined. Its parts are called sacral vertebrae when referred individually.
Variations
In some cases, the sacrum will consist of six pieces or be reduced in number to four.[8] The bodies of the first and second vertebrae may fail to unite.
Development
The
Clinical significance
Congenital disorders
The
Another congenital disorder is that of
Fracture
Sacral fractures are relatively uncommon; however, they are often associated with neurological deficits. In the presence of neurological signs, they are mostly treated with surgical fixation.[12]
Cancer
The sacrum is one of the main sites for the development of the
Other animals
In dogs the sacrum is formed by three fused vertebrae. The sacrum in the horse is made up of five fused vertebrae.[14] In birds the sacral vertebrae are fused with the lumbar and some caudal and thoracic vertebrae to form a single structure called the synsacrum. In the frog the ilium is elongated and forms a mobile joint with the sacrum that acts as an additional limb to give more power to its leaps.
History
English sacrum was introduced as a technical term in anatomy in the mid-18th century, as a shortening of the Late Latin name os sacrum "sacred bone", itself a translation of Greek ἱερόν ὀστέον, the term found in the writings of Galen.[15][16][10][17][18][19] Prior to the adoption of sacrum, the bone was also called holy bone in English,[20] paralleling German heiliges Bein or Heiligenbein (alongside Kreuzbein[21]) and Dutch heiligbeen.[20][22][23]
The origin of Galen's term is unclear. Supposedly the sacrum was the part of an animal offered in sacrifice (since the sacrum is the seat of the
In
Additional images
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Image of a female pelvis seen anteriorly, sacrum at centre.
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Lateral surfaces of sacrum and coccyx.
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Base of sacrum.
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Median sagittal section of the sacrum.
-
Left levator ani from within.
-
The posterior divisions of the sacral nerves.
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Sacrum. Pelvic surface.
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Sacrum. Dorsal surface.
-
Sacrum anatomy
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Sacrum (not labeled) seen on the right with sacral nerves, median sacral artery, and rectum on the lower left.
See also
- Bone terminology
- Pelvimetry
- Rump (croup)
References
This article incorporates text in the public domain from page 106 of the 20th edition of Gray's Anatomy (1918)
- ^ Oxford Dictionaries and Webster's New College Dictionary (2010) admit the plural sacrums alongside sacra; The American Heritage Dictionary, Collins Dictionary and Webster's Revised Unabridged Dictionary (1913) give sacra as the only plural.
- ^
Kilincer, Cumhur; et al. (2009). "Sacrum anatomy". Scientific spine. Trakya Üniversitesi Rektörlüğü, Yerleşkesi, 22030 Edirne, Turkey: Self. Retrieved 8 November 2015.
{{cite web}}
: CS1 maint: location (link) - ^ "Skeletal system" (PDF). Dept. of Biology. Gambier, Ohio: Kenyon College. Retrieved 9 November 2015.
- ISBN 0-520-24209-2.
- ISBN 1-57947-669-4.
- ^ Joseph D. Kurnik, DC (16 December 1996). "The AS Ilium Fixation, Nutation, and Respect".
- ^ Maitland, J (2001). Spinal Manipulation Made Simple. Berkeley: North Atlantic Books, p. 72.
- ^ Gray, Henry (1918). Anatomy of the Human Body. Lea & Febiger. pp. 111.
sacrum will consist of six pieces.
- ISBN 0-443-06583-7
- ^ a b Anderson, D.M. (2000). Dorland's illustrated medical dictionary (29th edition). Philadelphia/London/Toronto/Montreal/Sydney/Tokyo: W.B. Saunders Company.
- PMID 2180307.
- S2CID 6651435.
- ^ "Understanding Chordoma – Chordoma Foundation". www.chordomafoundation.org. Retrieved 7 April 2017.
- ^ King, Christine, BVSc, MACVSc, and Mansmann, Richard, VMD, PhD. "Equine Lameness." Equine Research, Inc. 1997.
- ^ a b Hyrtl, J. (1880). Onomatologia Anatomica. Wien: Wilhelm Braumüller. K.K. Hof- und Universitätsbuchhändler.
Geschichte und Kritik der anatomischen Sprache der Gegenwart
- ^ Liddell, H.G.; Scott, R. (1940). Jones, Sir Henry Stuart; McKenzie, Roderick (eds.). A Greek-English Lexicon. Oxford: Clarendon Press.
- ^ His, W. (1895). Die anatomische Nomenclatur. Nomina Anatomica. Leipzig: Verlag Veit & Comp.
Der von der Anatomischen Gesellschaft auf ihrer IX. Versammlung in Basel angenommenen Namen
- ^ Federative Committee on Anatomical Terminology (FCAT) (1998). Terminologia Anatomica. Stuttgart: Thieme.
- ^ Lewis, C.T.; Short, C. (1879). A Latin Dictionary. Oxford: Clarendon Press.
founded on Andrews' edition of Freund's Latin dictionary
- ^ a b c d Schreger, C.H.Th. (1805). Synonymia Anatomica. Fürth: im Bureau für Literatur.
Synonymik der anatomischen Nomenclatur
- ^ "cross bone", also of unclear origin. According to Grimm, Deutsches Wörterbuch (""Kreuz", meaning 8a".), Kreuz "cross" is used of the sacral area of the spine, but also of the spine as a whole, with usage examples from the 17th-century (Christian Weise, Isaacs Opferung, 1682, 3.11). Notabilia Venatoris by Hermann Friedrich von Göchhausen (1710) and Teutscher Jäger by Johann Friedrich von Flemming (1719, p. 94) also give kreuz as hunting terminology for a specific bone of the stag.
- ^ a b c Foster, F.D. (1891–1893). An Illustrated Medical Dictionary. New York: D. Appleton and Company.
Being a dictionary of the technical terms used by writers on medicine and the collateral sciences, in the Latin, English, French, and German languages.
- ^ Everdingen, J.J.E. van, Eerenbeemt; A.M.M. van den (2012). Pinkhof Geneeskundig woordenboek (12de druk ed.). Houten: Bohn Stafleu Van Loghum.
{{cite encyclopedia}}
: CS1 maint: multiple names: authors list (link) - ^ "sacrum". Online Etymology Dictionary.
- ^ a b Hyrtl, J. (1875). Lehrbuch der Anatomie des Menschen. Mit Rücksicht auf physiologische Begründung und praktische Anwendung (Dreizehnte Auflage ed.). Wien: Wilhelm Braumüller K.K. Hof- und Universitätsbuchhändler.
- ^ used by Antimachus; see Liddell, Henry George; Scott, Robert. "klo-nis". A Greek-English Lexicon.
- ^ Kraus, L.A. (1844). Kritisch-etymologisches medicinisches Lexikon (Dritte Auflage ed.). Göttingen: Verlag der Deuerlich- und Dieterichschen Buchhandlung.
External links
- Anatomy photo:43:st-0401 at the SUNY Downstate Medical Center – "The Female Pelvis: Bones"
- pelvis at The Anatomy Lesson by Wesley Norman (Georgetown University)