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X-Rays Explained

X-Rays Explained


Conference on Research and Education
Monterey, California June 21-23, 1991

Presenter: E.A. Addington, M.A., D.C.
Blair Chiropractic Clinic
Lubbock, Texas

The technique developed and taught by the late William G. Blair, D.C., Ph.C., F.I.C.A., is an exclusively cervical technique that considers subluxations of Cl through C4. (A number of contemporary practitioners extend the analysis and adjustive procedures through the entire cervical spine.) The presence of cervical nerve interference is established by observation of both persistent differential paraspinal derinothermographic pattern and functional leg length deficiency (traditionally assessed in the prone position). The misalignment component of the subluxation is demonstrated radiographically by means of specially developed spinographic views which are customized to each patient's anatomy.

Dr. Blair's spinographic research and clinical procedures (1,7) were propounded on his empirical observations (2-7) that clinically significant asymmetry "malformation" of bilateral structures usually employed in cervical spinographic analysis is the rule rather than the exception. The simplifying assumption underlying Dr. Blair's system is that, regardless of asymmetry, the opposing surfaces of a joint develop in such a way that their margins are identical in conformation. Therefore, properly-imaged and properly aligned articulations will demonstrate exact juxtaposition of adjacent articular surfaces at their osseous margins, while misaligned articulations will demonstrate certain observable and classifiable disappositions at their osseous margins. If vertebrae misalign, and in the absence of fracture, that misalignment must take place at the articulations. The articulation is therefore the most anatomically accurate place to assess the alignment of the vertebra.

Dr. Blair developed a two-stage system of visual spinographic analysis that permits assessment of vertebral alignment at the articular margins as those articulations are formed in each individual patient and which is therefore insensitive to violations of the assumption of bilateral symmetry. A scout series, traditionally comprised of Base Posterior, A-P Open Mouth, and five-degree rotated Lateral Cervical views, is used to determine the optimum angles from which to observe the atlantooccipital and apopyhseal articulations. An articular series, which includes Blair Oblique Protractoviews of each atlanto-occipital articulation and a Blair lateral Cervical Stereoscopic view made at a specified degree of rotation and tube elevation, is used to determine cervical articular alignment. The Blair Protracto clamp, a patented patient positioning device which permits the taking of cervical radiographs at specific degrees of rotation, is necessary to perform both the scout series and the articular series, which together comprise the Blair Cervical Series.

The Base Posterior view (which is similar to the diagnostic Submental Vertex view but must be free of appreciable head-tilt and must meet additional positioning criteria) is used to plot and measure the convergence any-les -representing the longitudinal axes) of the respective atlanto-occipital articulations according to a distinctive method originated by Dr. Blair. The Blair Princij2le of Atlanto-Occipital Misalignment states that, in the non-fractured and non-dislocated atlas, misalignment with respect to the occipital condyles occurs in an obliquely-anterior or obliquely-posterior direction parallel to one or both of the atlanto-occipital convergence angles. The Base Posterior view is also used to study osseous asymmetry of the foramen magnum, condyles, lateral masses, and spinal canal; to assess deviations in the course of the neurological contents of the foramen magnum and cervical spinal canal; to study the formation of atlas transverse processes and posterior arch for adjustive considerations, and to contribute information for the selection of an ipsilateral or contralateral adjustive contact. The convergence angle is also used in adjusting certain atlas listings.

The A-P Open Mouth view is used to study lateral deviations of the neural rings which may be causing brainstem or cord pressure, asymmetries of occipito-atlanto-axial structures and their resulting developmental or biomechanical compensation patterns, and apparent spinus process rotations. In conjunction with the 5-degree-rotated scout Lateral Cervical view, the A-P Open Mouth view is also used to prescribe the direction and amount of patient rotation (usually from 0 to 5 degrees) and central ray placement superior-to-inferior ( usually at the level of the external auditory meatus or of the lower cervicals) for best visualization of the C2-4 articulations on the Blair Lateral Cervical Stereoscopic view. Some contemporary practitioners omit the scout Lateral Cervic view take 5-degree rotated Lateral Cervical Stereoscopic views the left and the right sides to obtain more complete visualization of the articulations from C2 inferiorward.

Blair Oblique Protractoviews of each atlanto-occipital articulation are made with the patient turned in a positioning chair secured in Blair Protracto clamps at an angle equal to the convergence angle of the articulation being studied, so that the central ray is directed obliquely anterior-to-posterior along the convergence angles of each of the respective articulations. In this manner the antero-lateral (distal) margins of each of the articulations may be clearly imaged (often by means of stereoscopic views, depending upon the amount of superimposed osseous densities) and trichotomously classified as being either juxtaposed, overlapped (atlas lateral mass margin more anterolateral than condyle margin), or underlapped (lateral mass margin less antero-lateral than condyle margin). These appositional judgments of each articulation may then be combined to deduce the actual unilateral or ambilateral misalignment pathway(s) of atlas in relation to occiput, and an anatomically accurate misalignment listing and adjustive formula may thus be derived.

The Blair Lateral Cervical Stereoscopic view, or the alternative bilateral rotated lateral Cervical Stereoscopic views, are read using a stereo viewbox or stereo binoculars, permitting differentiation of the left and right apophyseal articulations and three dimensional visualization of the neural canal. Appositional determinations are made at the anterior margins of the apophyseal articulations, and the superior vertebra is listed as being either juxtaposed, misaligned anterior-superior, or misaligned posterior-inferior at the articular margin on each side. Corresponding anterior or posterior displacements of the posterior aspect of the vertebral body is usually observable on the side of a posterior-joint misalignment. Stereoscopic study of the course of the neural canal of these views is of great importance in determining the segment(s) to be adjusted.

In some cases the posterior articulations between C2 and C3 will be observed to be formed with a semi-sagittal joint plane. In these cases, C2-C3 apposition is usually determinable from the Blair Oblique Protractoviews, on which the margins of these "turned articulations" will ordinarily be satisfactorily visible. In rare cases, special Blair Axis Views, taken through the ocular orbit or the open mouth, may be necessary to list C2.

Measurement studies of the convergence angles (8) have demonstrated interovserver reliability (Pearson product- moment correlation coefficients) ranging from .84 to .90 among experienced clinicians using the same measurement procedures (p less than .01). Means of convergence angles on the right and the left sides were not found to differ to a statistically significant extent (p greater than . 10). Convergence angles of left and right articulations, pooled together, showed a mean value of about 24.3 plus or minus 1.6 degrees, with a range of 6 to 58 degrees and a standard deviation of about 8 degrees, in a sample of 45 cases. A weak correlation between convergence angles within subject was found (r = .40, p less than .01). A mean difference in convergence angle measurements within subject of 7.25 -+ 1.5 degrees was observed, with a range of .5 degrees and a standard deviation of 5.2 degrees.

Interobserver reliability of appositional measurements at atlanto-occipital articular margins has been reported to range from .65 to .79 (Pearson r; p less than .005) on Blair Oblique Protractoviews (9). Condylar slope measurements from these views, used in the majority of atlas adjustment formulas, demonstrated interovserver reliability ranging from .81 to .92 (Pearson r; p less than .005), while measurements of posterior condylar convexity, used in some atlas adjustments, ranged from .21 to .84 (Pearson r; p less than .05) inb interobserver reliability due to slight differences in measurement methods. Interobserver reliability of articular determinations subjacent to atlas has not yet been investigated, although such a project is currently in the early stages of design (10).

Considering only C1 through C4, and taking account of observed or reasonable ranges of convergence, condylar slope and convexity, atlas plane line, and articular slopes of C2-C4, it has been estimated that at least 578, 782 distinct adjustments of the upper cervical spine exist within the Blair system (11). Specificity is critical to proper utilization of the technique.


  1. Blair, Wm.G. Primary Seminar. Advanced Seminar. Five-Day Seminar. Various U.S. locations, ca. 1961-1980.
  2. Blair, Wm. G. A synopsis of the Blair upper cervical
    Spinographic research. Science Review of Chiropractic (International Review of Chiropractic: Scientific Edition) I (1) : I- 19 (Nov. 1964)
  3. Blair, Wm. G. For evaluation; for progress. Intl. Rev. Chiro. 22 (8) :8-11 (Feb. 1968)
  4. Blair, Wm. G. For evaluation; for progress. Intl. Rev. Chiro. 22 (9): 10-14 (Mar. 1968)
  5. Blair, Wm. G. For evaluation; for progress. Intl. Rev. Chiro. 22 (12):14-16 Pun. 1968)
  6. Blair, Wm. G. The big idea: what is it? Intl. Rev. Chiro. 23 (2):13-14 (Aug. 1968)
  7. Blair, Wm. G. Blair Upper Cervical Spinougphic Research Primary and Adaptive malformations, Procedures for Solving Malformation Problems: Blair Principle of Occipito-Atlanto Misalignment. Ph.C. Thesis, Palmer College of Chiropractic, 1968
  8. Addington, E.A., M.G. Howard, M.A. Pruitt, and C.E. Spears. Objectivity of Blair atlanto-occipital articular convergence angle measurements. Third Annual Upper Cervical Symposium, Dec. 5-7, 1968, Life Chiropractic College, Marietta, GA. (Earlier version presented at First Annual Convention and Educational Seminar, Wm. G. Blair Chiropractic Society, Inc., Oct. 24-26, 1968, Lubbock, TX.)
  9. Addington, E.A., F. Harkins, R.I. Morrison, R.W. Muncy, and P.Rush. Interobserver reliability (objectivity) of atlanto-occipital appositional measurement and condylar slope and convexity measurements on Blair Oblique view spinographs. Third Annual Convention and Educational Seminar, Wm G. Blair Chiropractic Society, Inc., October 7-8, 1988, Sommerville (Boston), MA. (Earlier version presented as Objectivity (interobserver reliability) of atlanto-occipital articular appositional determinations and slope angle measurement in Blair upper cervical technique. Fourth Annual Upper Cervical Conference, Dec. 4-6, 1987, Life Chiropractic College, Marietta, GA.)
  10. Addington, E.A., et.al., in progress.
  11. Addington, E.A., and R.W. Muncy. Estimated number of distinct upper cervical adjustments in
    Blair technique. Fourth Annual Convention and Educational Seminar, Wm.G. Blair Chiropractic
    Society, Inc., Oct. 28-29, 1989 Kansas City, MO.
  12. Addington, E.A., M. Banitch, R. Morrison, and C. Roberts. Interobserver reliability of neural canal diameters and neural canal relationships in A-P open mouth cervical spinographs. Tenth Annual Conference, Wm. G. Blair Chiropractic Society, Inc., Seattle, WA. Aug. 4-6, 1995

Reprinted by permission from the Proceedings of the Sixth Annual
Conference on Research and Education: "Emphasis on Consensus."
June 21-23, 199 1, Monterey, California.
Program Sponsors:
Consortium for Chiropractic Research, California Chiropractic
Association, ACA Council on Technique.


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