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During about the sixth month of fetal life, two centres make their appearance in the base of this process: they are placed laterally, and join before birth to form a conical bilobed mass deeply cleft above; the interval between the sides of the cleft and the summit of the process is formed by a
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The internal structure of the odontoid process is more compact than that of the body. The odontoid peg is the ascension of the atlas fused to the ascension of the axis. The peg has an articular facet at its front and forms part of a joint with the anterior arch of the atlas. It is a
263:. The inner ligaments limit rotation of the head and are very strong. The weak apical ligament lies in front of the upper longitudinal bone of the cruciform ligament and joins the apex of the deltoid peg to the anterior margin of the foramen magnum. It is the fibrous remnant of the
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The base of the process is separated from the body by a cartilaginous disk, which gradually becomes ossified at its circumference, but remains cartilaginous in its center until advanced age.
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are broad and strong, especially in the front, where they coalesce with the sides of the body and the root of the odontoid process. They are covered above by the superior articular surfaces.
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Type II fracture - Extends through the base of the dens. It is the most commonly encountered fracture for this region of the axis. This type is unstable and has a high rate of non-union.
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Jumah, Fareed; Alkhdour, Saja; Mansour, Shaden; He, Puhan; Hroub, Ali; Adeeb, Nimer; Hanif, Rimal; Mortazavi, Martin M; Tubbs, R. Shane; Nanda, Anil (2017).
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The centres for the arch appear about the seventh or eighth week of fetal life, while the centres for the body appear in about the fourth or fifth month.
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The apex of the dens has a separate centre that appears in the second and joins about the twelfth year; this is the upper epiphyseal plate of the atlas.
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and may cause nerve and circulation compression syndrome. On its anterior surface is an oval or nearly circular facet for articulation with that on the
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The dens, or odontoid process, consists originally of a continuation upward of the cartilaginous mass, in which the lower part of the body is formed.
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The body is deeper in front or in the back and is prolonged downward anteriorly to overlap the upper and front part of the third vertebra.
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Type III fracture - Extends through the vertebral body of the axis. This type can be stable or unstable and may require surgery.
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are round, slightly convex, directed upward and laterally, and are supported on the body, pedicles, and transverse processes.
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In addition to these, there is a secondary centre for a thin epiphyseal plate on the undersurface of the body of the bone.
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are thick and strong. They play a large role in the stability of the cervical spine alongside the laminae of C7.
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It presents a median longitudinal ridge in front, separating two lateral depressions for the attachment of the
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Fractures of the dens are classified into three categories according to the
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The body and vertebral arch are ossified in the same manner as the corresponding parts in the other
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is large, very strong, deeply channelled on its under surface, and presents a bifurcated extremity.
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Posterior atlantooccipital membrane and atlantoaxial ligament; the axis is visible at center.
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This article is about a bone named the Axis. For an anatomical axis such as AP or ML, see
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Its shape and position (shown in red) from above. The skull is shown in semi-transparent.
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which retains the process in position. The apex is pointed and gives attachment to the
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are very small, and each ends in a single tubercle. Each process is perforated by the
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Knowledge articles incorporating text from the 20th edition of Gray's
Anatomy (1918)
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Median sagittal section through the occipital bone and first three cervical vertebra
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Type I fracture - Extends through the tip of the dens. This type is usually stable.
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of the atlas, and the upper epiphyseal plate of the axis may sometimes be found.
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The inferior articular surfaces have the same direction as those of the other
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The defining feature of the axis is its strong bony protrusion known as the
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for individuals with anomalous dens, as any violent impact may result in a
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734:"The role of the vertebral laminae in the stability of the cervical spine"
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The axis is ossified from five primary and two secondary centers.
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675:"Os Odontoideum: A Comprehensive Clinical and Surgical Review"
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A fracture of the base of the dens as seen on plain X-ray
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781:(3 ed.). American Academy of Orthopaedic Surgeons.
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Axis on X-ray taken through an open mouth, teeth visible
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Second cervical vertebra, or epistropheus, from above
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A fracture of both pedicles of the axis is termed a
308:, which is directed obliquely upward and laterally.
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Sagittal section of nose mouth, pharynx, and larynx
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489:A fracture of the base of the dens as seen on CT
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255:joint. The alar ligaments, together with the
243:; these ligaments connect the process to the
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732:Pal, G. P.; Routal, R. V. (April 1996).
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329:are very shallow, and lie behind the
23:Second cervical vertebra of the spine
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18:Anatomical terminology § Axes
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777:Schenck, Robert C., ed. (1999).
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233:transverse atlantal ligament
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618:Unfused arch of atlas at CT
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1138:anterior sacral foramina
501:Type 3 odontoid fracture
363:and axis (the C1 and C2
237:apical odontoid ligament
157:, "axle") is the second
129:Anatomical terms of bone
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912:Intervertebral foramen
808:Atlas of Human Anatomy
630:anatomical terminology
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428:Clinical significance
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1167:Lateral sacral crest
544:Axis seen from above
513:Type 2 dens fracture
302:transverse processes
197:longus colli muscles
1403:Bones of the thorax
1162:Medial sacral crest
1157:Median sacral crest
692:10.7759/cureus.1551
357:catastrophic injury
331:articular processes
1351:Infrasternal angle
1313:Xiphisternal joint
1293:Suprasternal notch
1026:Thoracic vertebrae
1016:Vertebra prominens
977:Posterior tubercle
962:Transverse foramen
949:Cervical vertebrae
814:2017-11-20 at the
738:Journal of Anatomy
628:This article uses
447:Hangman's fracture
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365:cervical vertebrae
320:cervical vertebrae
313:articular surfaces
306:transverse foramen
219:, also called the
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907:Vertebral foramen
873:General structure
519:Additional images
327:vertebral notches
291:vertebral foramen
169:, upon which the
159:cervical vertebra
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225:os odontoideum
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371:Development
175:spinal cord
173:rests. The
63:Identifiers
1392:Categories
1236:false ribs
1084:mammillary
1049:transverse
922:transverse
636:References
1298:Manubrium
1231:true ribs
1079:accessory
1074:Processes
927:articular
917:Processes
865:Vertebrae
746:0021-8782
701:2168-8184
433:Fractures
392:vertebrae
344:Variation
265:notochord
188:Structure
1258:tubercle
1218:Rib cage
1044:inferior
1039:superior
812:Archived
719:29018648
624:See also
558:3D image
385:ossified
277:pedicles
1382:Anatomy
1285:Sternum
932:spinous
890:pedicle
855:of the
764:8621347
755:1167584
710:5630463
652:page 99
284:laminae
149:, the
147:anatomy
86:D001368
58:Details
1368:Portal
1209:Thorax
1189:Coccyx
1096:Sacrum
895:lamina
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679:Cureus
660:(1918)
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982:Atlas
900:notch
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650:from
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295:atlas
167:atlas
163:spine
133:[
122:12520
69:Latin
1273:head
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1226:Ribs
1196:none
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1009:dens
1004:Axis
885:Arch
880:Body
783:ISBN
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351:are
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217:dens
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211:Dens
206:Axis
182:dens
171:head
155:axis
151:axis
110:1050
93:TA98
81:MeSH
29:Axis
750:PMC
705:PMC
687:doi
367:).
145:In
117:FMA
105:TA2
1394::
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838:t
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20:.
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