Atlas-axis facet asymmetry. Implications in manual palpation

A basic study of six human cervical spines, documenting displacement with applied forces mimicking palpation.

To assess the issues of motion palpation of joint restrictions and the inferred link to disease.

Although several investigators have suggested that the issue of asymmetry and normal-abnormal function should be assessed, data are unavailable.

Atlas-axis specimens were harvested from six cadavers, cleaned of ligamentous and muscle tissue, and potted and secured with dental plaster. Forces (5-25 N) were applied along the mediolateral axis, and the corresponding displacement along three orthogonal axes were documented with infrared diodes and the Optotrak camera system (Northern Digital, Waterloo, Ontario, Canada). Specimen geometry and asymmetry were documented with plain radiographic film and a gimbal apparatus.

Each of the six specimens displayed different behavior and differing degrees of asymmetry (e.g., facet inclination 17-35 degrees) so that each was analyzed as a case study. Asymmetrical and discontinuous force-displacement correlations were linked to anatomic asymmetry that appeared to be of natural occurrence.

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.