Atlas–Axis Facet Asymmetry

Abstract

Asymmetrical joint geometry is common and causes asymmetrical joint dynamics. Thus, a clinician attempting to palpate vertebral motion would be misled by assuming that perceived restricted joint motion universally represented a finding potentially amenable to manipulation. For spine palpation to be a valid indicator for manipulation, the clinician applying it must first be able to differentiate between asymmetrical motion caused by vertebral fixation and that caused by asymmetrical joint anatomy.

The effect of talocrural joint manipulation on range of motion at the ankle

“…It suggests that such a discrepancy in an asymptomatic individual is 'normal' and should not be assumed by therapists to be necessarily 'dysfunctional'. This is consistent with other studies that have indicated asymmetries of joint geometry and ROM in other regions, such as the atlas-axis articulation 27 and sacroiliac joint 28,29 , are commonly found in normal populations.…”

Principal Components Analysis of the Atlas Vertebra

“…Because of a longer articular path on one facet, the range of motion would be accentuated on one side as compared to the other side creating not only structural asymmetry but also functional asymmetry. 2 With the dominant role of the atlantoaxial joint being rotation, there may be a relationship between variation in the morphology of the inferior facet and interpretation of both static and motion palpation results. 2,16 Variation in the structure of the atlantoaxial joint (especially variation that impacts rotation) may have significant biomechanical impact leading to upper cervical dysfunctions such as muscle spasm (especially torticollis).…”

“…A restricted motion because of natural variation (in a joint that would normally be freely movable) may wrongly suggest an abnormal position. 2 Although there is a wealth of information regarding variability and asymmetry in the normal cervical spine, symmetry is still largely assumed for the analysis, diagnosis, and management of the vertebral malposition. This holds true for many chiropractic techniques such as Gonstead, National Upper Cervical Chiropractic Association, and Atlas Orthogonal.…”

“…[2][3][4][5][6][7][8][9][10][11][12] Variations in both the occipital condyles and atlas have previously been shown in both cadaveric specimens using dissected tissues and live patients using radiographs. 2,[6][7][8][9]12 Variation in the geometry of the atlantooccipital joint may cause asymmetrical joint dynamics such as unequal occipital extension on the atlas when compared bilaterally. This may then lead to errors of interpretation based on palpation and the assumption that a perceived restricted joint motion represents a malposition.…”

“…Although the aforementioned studies discuss some form of variation, none specifically identify true asymmetry as a statistical construct (ie, sides differ statistically). 1,2,[7][8][9]12 A second, more important problem in most of the previous studies is that of experimental design. Many of these articles are univariate studies, often using simple procedures (z statistic, Student t test, or simple inspection) for analysis, making it difficult at best to understand variability in the entire dataset across multiple variables without increasing the probability of error.…”