- -

The Atlas Sagittal Plane

T he atlas sagittal plane is con-structed from the. sagittal cervi-cal x-ray (Fig.1). The atlas sag-

ittalplane (ASP)is necessary to estab-lishso that the atlas frontal plane x-ray .

is takento observethe atlasat a directfrontal plane view. On the frontalplane,we do not want to lookat theatlas from a supe-rior or inferiorview.

In the atlasorthogonal pro-gram, we takethe sagittalx-rayviewfirst and es-tablish the ASPline and then wetake the frontalplane x-ray.Using a Coor-dinate System

White andPunjabi, in theirbook ClinicalBiomechanicsof the Spine,recommend thata three-dimen-sionalcoordinatesystembeusedtodocument thecomplete me-chanical behavior of spinal motionsegmentsand functionalbiomechanicsof the spine. They recommend theright-handed Cartesian orthogonalcoordinatesystem.

"The suggested central coordi-nate systemwith its originbetween the

ASP 3 ...

ASP 2

ASP 1

ASPD

~ W. Sweat, D.C.

cornua of the sacrum is shown. Itsorientation is as follows: The -y-axisisdescribed by the plumb line droppedfrom the origin, and the +x-axispointsto the leftat a 90-degree angle to the y-axis. The +z-axis points forward at a9O-degree angle to both the y-axis andthe x-axis. The human body is shown in

ATLAS SAGGrI'AL PLANE

c: 1987 Dr. Roy W. SweatAtlanta,Georgia 30341

the anatomic position. There are somebasic conventions that are observedwhich make this a useful system. Theplanes are as shown: The sagittalplaneis the y,z plane; the frontal plane is they,x plane; and the horizontal piane isthex,z plane. Movementsare described

in relation to the origin of the coordi-nate system. The arrows indicate thepositive direction of each axis. The~rigin is the zero point, and the direc-tion opposite to the arrows isnegative." (Fig.2)Constmcting the ASP Une

We mark the inferior border ofthe posteriorarch where itjoins the atlas.lateral mass asour first land-mark. We thenmove posteri-orly along theinferiorborderof the poste-rior arch forone-quartertoone-half inchand put a sec-ond marking.We then con-structourASPline throughthese twopoints ex-tended to theanterior facialfeatures. AllASPlines0 orlower should

be taken as A-P open-mouth views.There are three growth centers in

the atlas, one in each lateral mass andone in the anterior arch. On the frontalx-ray, the inferior border of the poste-rior arch will be horizontal and in thecenter of the lateralmasses. EachASP

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x,z

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line willaverage seven degrees. We findthat 90 percent of the ASP lines willbe1,2, and3.

About the author: Roy W. Sweat, D.C., Is anoted author, lecturer, and researcher whomaintains a prlootepractice. Forfurther Infor-mation, write to him at 3274 Buckeye Road,N.E., Atlanta, Georgia30341.

References1. Whiteand Punjab!,ClinicalBiomechanicsofthe Spine, (Reprintedwith pelTTlisslon),Uppln-cott, 1978, p. 62.2. Warwick and Williams, Gray's Anatomy,35th ed., p. 246, W.B. SaundersCo., 1973.3. Case Studies, Sweat ChiropracticClinic.

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