Atlas- AxisBody Relationship

The aXis body will always bemisaligned to the laterol sideopposite the laterality of thelower angle. The axis bodyshould never be disrelated tothe same lateral side that thelower cervical spine is laterallymisaligned.

I n the nasi urn dimension there isa relationship of the atlas-axisbody that corresponds to the

lateral movement of the lower cerv-ical spine. The atlas-axis body medialto lateral movement will be neutral inthe relationships of the odontoid tothe internal lateral mass spaces undernormal amatomical and neutral lowercervical spine positioning. (Fig. 1)

The articulation of atlas and axiscomprises three synovial joints - oneon each side between the inferiorfacet of the lateral mass of the atlasand the superior facet of the axis, andthe other mediaL between the densand the anterior arch and transverseligament of the atlas. The lateralatlanta-axial joints are classified asplane joints but the articular surfacesinvolved are both sJjghtly convex intheir long axes. The median atlanto-axial joint is a pivot joint between thedens of the axis and the ring formedby the anterior arch and the trans-

TodoV's Chiroproctic/September-October. 1986

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By Roy W. Sweat. D.C.

verse ligament of the atlas.The bodies of the vertabrae in the

cervical area are arcuated, and thejoints of Luschka in the cervical areamaintain a continuity of directionalmovement When one of the cervicalvertebrae moves laterally, the inter-osseous lockingof the vertebralbodiescauses the vertebra above to movelaterally in the same direction. Thebodies from seventh cervicalthroughthe axis body will follow the move-ment. Theinferior atlas facets and thesuperior axis facets have no interos-seous locks and are synovial joints;consequently, the atlas can subluxateright or left of the axis body.Ligaments

Eightstrongligamentshelp maintainthe atlas and axis body in a neutral orjuxtaposition. Ligaments permit safeand smooth movement but help pre-vent and check trauma.

The transverse ligamentofthe atlasis a thick,strong band whic~attachesfrom the internal lateral masses,arches around the posterior dens andretains the dens in contact with theanterior arch. As it crosses the dens alongitudinalband isprolonged upwardand attaches to the basilar part of theoccipitalbone. Alowerband prolongsdownward and attaches to the pos-terior surface of the axis body. It isthen knownas the cruciformligamentThe tectorial (ligament)membrane isthe upward continuation of the pos-terior longitudinal ligament. It is fan-shaped, broad and strong andstretches from the basilar groove ofthe occipitalbone downward overtheposterior surfaces of the vertebralbodies. It coversthe odontoid process,givingadded strengthto the transverseligament of the atlas.

This ligamenthas also an accessory(deep) portion with fibers more later-allyplaced and stretches from the la-teral margins of the anterior foramen

magnum to the upper postero-lateralportions of the body of the axis. Thealar ligaments extend from the densto the lateral margfns of the foremenmagnum. These strong, short, roundedcords, which are almost as thick aspencils, check lateral rotation andside-to-side movements of the headand attach the skull to the axis. Thearticular capsule joins the posteriorarticular surfices of the axis with themargins of the lateral masses of theatlas. The accessory ligament is a re-inforcement of the posterior medialmargin. It attaches below to the bodyof the axis near the base of the dens,and above to the lateral mass of theatlas near the transverse ligament.

The atlanto (axial)-epistrophic liga-ment is a strong fibrous band extend-ing from the anterior arch of the atlasto the front of the body of the axis.The apicialligament extends from thetip of the dens to the internal surfaceof the occipital bone. The anteriorlongitudinal ligament isa strong narrowband of fibrous tissue extending fromthe base of the skull down to the an-terior midportion of the vertebralbodies to the sacrum.Axis Body-Lower Cervical SpineRelationship

When the lower cervical spine hasmoved laterally one to five ,degrees,the relationship of the atlas-axis bodywill be neutral. The atlas laterality list-ings and the axis body listings will bethe same. There is some small degreeof lateral movement of the lower cer-vical spine before the atlas-axis bodyrelationship is disrupted.

When the lower cervical spine hasmoved laterally five to 10 degrees,the axis body will be disrupted onedegree, based on a three-inch con-dular circle, in its relationship to theatlas. When the lower cervical spine is10 to 15 degrees degrees, the axisbody will be disrupted two degrees in

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