3 Atlanto-Occipital Anatomy



10.1055/b-0039-166412

3 Atlanto-Occipital Anatomy

Suzanne Labelle, Fady Y. Hijji, Ankur S. Narain, Philip K. Louie, Daniel D. Bohl, and Kern Singh

3.1 Bony Anatomy



3.1.1 Occipital Bone


(Fig. 3.1)




  • External occipital protuberance.



  • Superior nuchal line.



  • Inferior nuchal line.



  • Occipital condyle:




    • Articulate with superior facets of the atlas vertebra.

Fig. 3.1 Bony anatomy of occipital bone. (Reproduced with permission from Bambakidis NC, Dickman CA, Spetzler RF, Sonntag VKH, eds. Surgery of the Craniovertebral Junction. 2nd edition. New York, NY: Thieme; 2012)


3.1.2 Atlas: First Cervical Vertebra (C1;)


(Fig. 3.2)




  • Foramen magnum:




    • Allows passage of spinal cord.



  • Anterior arch:




    • Anterior tubercle.



    • Articular facet for dens on posterior surface.



  • Posterior arch:




    • Equivalent to lamina of other cervical vertebrae.



    • Posterior tubercle:




      • Equivalent to spinous process.



  • Transverse process:




    • Contains transverse foramen:




      • Allows for passage of vertebral artery.



      • Vertically oriented.



  • Lateral masses:




    • Equivalent to vertebral body (no formal vertebral body).



    • Contains tubercle for attachment of cruciate ligament.



    • Superior articular surface:




      • Horizontally oriented.



      • Articulates with occipital condyle forming atlanto-occipital joint:




        • Biaxial condyloid synovial joint: fluid-filled articulations involving occipital condyles that allow movement in two planes.



        • Permits flexion and extension; minimal lateral bending and rotation.



    • Inferior articular surface:




      • Horizontally oriented.



      • Articulates with lateral mass of axis forming atlanto-axial joint.

Fig. 3.2 Bony anatomy of atlas and axis. (Reproduced with permission from Bambakidis NC, Dickman CA, Spetzler RF, Sonntag VKH, eds. Surgery of the Craniovertebral Junction. 2nd edition. New York, NY: Thieme; 2012)


3.1.3 Axis: Second Cervical Vertebra (C2;)


(Fig. 3.2)




  • Dens:




    • Unique to only C2.



    • Anterior articular facet:




      • Articulates with anterior arch of atlas.



      • Forms median pivot joint ( Fig. 3.3 ).



    • Posterior articular facet:




      • Serves as articulating surface for the transverse ligament of the cruciate ligament:




        • Prevents subluxation between C1 and C2.



    • Small vertebral body beneath dens:




      • Small pedicles attaching to lateral masses.



  • Transverse process:




    • Contains transverse foramen:




      • Vertebral artery exits here:




        • Makes a 45-degree turn and re-enters cervical spine at transverse foramen of C1.



  • Spinous process:




    • Small and bifid.



  • Lateral masses:




    • Superior articular facet:




      • Horizontally oriented.



      • Articulates with atlas forming atlantoaxial joint:




        • Uniaxial synovial joint: fluid-filled joint that allows movement in one plane.



        • Plane joints between both superior articular facets of axis and corresponding inferior articular facets of atlas.



        • Median pivot joint between dens and anterior arch of atlas.



        • Permits side-to-side head rotation (50% of cervical rotation).



        • Permits small degree of flexion/extension (10 of 110 degrees of the cervical spine).



    • Inferior articular facet:




      • Horizontally oriented.



      • Articulates with C3 ( Table 3.1 ).

Fig. 3.3 Atlantoaxial joint side-to-side rotation. (Reproduced with permission from Bambakidis NC, Dickman CA, Spetzler RF, Sonntag VKH, eds. Surgery of the Craniovertebral Junction. 2nd edition. New York, NY: Thieme; 2012)
























Table 3.1 Comparison to other cervical vertebrae

Vertebra

Similarities

Differences

Atlas (C1)

  

Posterior arch in place of lamina


Posterior tubercle in place of spinous process


Anterior arch with anterior process


Axis (C2)

Spinous process Vertebral body

Articular processes in place of lamina


Dens/odontoid process


Both

Transverse processes with foramina for vertebral artery Articular surfaces on lateral masses

No uncinate processes


Lateral masses in place of body



3.2 Ligamentous Anatomy


(Tables 3.2, 3.3; Figs. 3.4, 3.5)

Fig. 3.4 Internal ligaments of craniocervical junction. (Reproduced with permission from Baaj AA, Mummaneni PV, Uribe JS, Vaccaro AR, Greenberg MS, eds. Handbook of Spine Surgery. 2nd edition. New York, NY: Thieme; 2016)
Fig. 3.5 Sagittal view of external ligaments of craniocervical junction. (Reproduced with permission from An HS, Singh K, eds. Synopsis of Spine Surgery. 3rd ed. New York, NY: Thieme; 2016)





















































Table 3.2 Atlanto-occipital ligaments ( Figs. 3.5, 3.6 )

Ligament

Origin

Insertion

Function

Anterior


Anterior atlanto-occipital membrane (AAO)

Anterior aspect of atlas

Anterior rim of foramen magnum

Limits extension of head


Barkow’s ligament

Anteromedial aspect of occipital condyle anterior to alar ligament

Anteromedial aspect of occipital condyle anterior to alar ligament

Limits extension of atlanto-occipital joint


Lateral atlanto-occipital ligament (LAO)

Anterolateral transverse process of axis

Jugular process of occipital bone

Limits lateral flexion of the head


Posterior


Posterior atlanto-occipital membrane (PAO)

Posterior arch of atlas

Posterior rim of foramen magnum

Posterior reinforcement of joint


Tectorial membrane

Posterior axis

Upper surface of occipital bone anterior to foramen magnum

Restricts extension at atlanto-occipital joint (continuation of posterior longitudinal ligament)


Posterior atlanto-occipital membrane (PAO)

Posterior arch of atlas

Posterior rim of foramen magnum

Posterior reinforcement of joint


Nuchal ligament

Spinous process of C7

Inferior projection of occipital bone

Restricts hyperflexion of cervical spine (continuation of supraspinous ligament)

















































Table 3.3 Atlantoaxial ligaments

Ligament

Origin

Insertion

Function

Anterior


Cruciate ligament (transverse atlantal ligament)

Lateral tubercle of atlas

Lateral tubercle of atlas of opposite site

Maintains stability of atlantoaxial junction by locking odontoid process against anterior arch of C1 Strongest ligament of the atlantoaxial joint


Alar ligaments

Lateral aspect of odontoid process

Base of skull

Limits hyperrotation and lateral bending on contralateral side


Transverse occipital ligament (TOL)

Inner aspect of occipital condyle

Inner aspect of occipital condyle

Sits posterosuperiorly to alar ligaments and assists them in support of craniocervical junction


Posterior


Accessory atlantoaxial ligament

Medial dorsal surface of axis

Posterior to transverse ligament on lateral mass of atlas

Protection and support for branches of vertebral artery that supply the dens


Tectorial membrane

Posterior axis

Upper surface of occipital bone anterior to foramen magnum

Restricts flexion/extension at atlantoaxial joint


Nuchal ligament

Spinous process of C7

Inferior projection of occipital bone

Restricts hyperflexion of cervical spine

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May 17, 2020 | Posted by in NEUROSURGERY | Comments Off on 3 Atlanto-Occipital Anatomy

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