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To the Editor:
It is encouraging to see new, clinically relevant upper cervical anatomical research; and no Blair practitioner will be surprised by the findings of Briggs et al1 of bilateral asymmetry of the atlantooccipital (AO) articulations. However, several of the references of Briggs et al to Blair's hypothesis on the matching of ipsilateral AO surfaces, his research database, and his radiographic analysis require clarification.
Blair2 does state broadly that “the articulations of the body perfectly match at the articular surfaces”; but he subsequently restricts his consideration to the3 “comparison of articular surfaces at their margins,” advancing no specific hypothesis as to surface areas. Finding that the medial margins of the AO articulations are “seldom well-defined” and “do not offer us articular surface comparison,” he developed the Blair Oblique Protractoviews specifically to image the most anterolateral or “distal condyle lateral mass margins” parallel to the longitudinal axis of each articulation.4 Viewing even these distal margins at too posterior4 or too anterior5 a point can be misleading as to articular alignment.
Blair's research was based not on “matched and unmatched” cadaver specimens with cartilage attached, but primarily on hard tissue “stereoscopic [i.e., three-dimensional] study of hundreds of Cranial-Atlanto-Axial-Cervical spinographs” (precision postural radiograph meeting chiropractic standards)2 and on malformation data from “anatomical measurement” of dry specimens in the BJ Palmer Osteological Collection supplied by Dr LG Fraser.4 Thus, the findings of Briggs et al are essentially peripheral to Blair's assertions, which invariably refer to osseous, not soft tissue, margins. Nevertheless, several potential sources of investigational error should be noted.
The cleaning itself, however meticulous, of the acute distal edges of lateral mass vs the obtuse (and often very short and indistinct) distal edges of the condyle presents 2 distinct psychomotor challenges to the hand. Any potential systematic error thus introduced would be compounded for methods 2 and 3 of Briggs et al by the “cut[ting] out,” by unspecified but presumably equally vulnerable means, of the aluminum foil molds.
For all 3 methods of Briggs et al, the outlines obtained will indeed depend, as the authors suggest, on the exact angle at which the mold or anatomical material is mounted with respect to the projectional surface. However, this is not a “minor measurement flaw” but a major source of potential error that must be carefully controlled in clinical practice.4,5 Consistent measurement is not necessarily correct measurement.
Briggs et al state that their method 3 is the most relevant because it mimics what is seen on the Blair Protractoviews.1 Their method looks at the image mimicking a base posterior or vertex radiograph (a coronal view). Blair insisted that the relationships of the condylar and lateral mass distal margins should not be assessed from the coronal view at all, but from a diagonally vertical perspective and “on a plane 90° to the [slope of the] articulation.”4 Therefore, the conclusion of Briggs et al comments on radiographic images that they did not study in their article.
A more technical exposition of Blair's hypotheses, observations, and methods as related to the procedures of Briggs et al is available at www.blairchiropractic.com. Hopefully, such studies as that of Briggs et al will stimulate further investigation into this pivotal area of the spine.