MORPHOLOGICAL ASYMMETRY OF THE ATLAS AND ITS CLINICAL IMPLICATIONS

Objective: The aim of this study was to investigate the asymmetry of the adult atlas by deviation frequencies using 3-dimensional (3D) computer models based on the computed tomographic (CT) spine data from healthy patients. Methods: Sixty adult atlas computer models were reconstructed from CT data of the cervical spine. The morphological asymmetries were investigated and measured with 3D software. Asymmetry in the morphology of the vertebral artery groove was observed, and the angles between the lines connecting the apices of transverse processes and the apices of anterior and posterior tubercles were measured. The lengths of the left and right posterior arches were measured, and the differences in values were categorized. Results: We observed 7 cases (11.67%) with asymmetrical vertebral artery groove forms. There were 4 different categories: foramen-shaped, semi-foramen-shaped, deep, and superficial grooves. The asymmetry was of different shapes on both sides. Relative to the lines connecting the apices of anterior and posterior tubercles, the asymmetry frequency of the transverse processes and the posterior arch length was 6.67% and 16.67%, respectively. Conclusions: For the specimens in this study, variation in morphology of the atlas was common. Asymmetry of apices of transverse processes, posterior arches, and vertebral artery grooves should be taken into account during clinical palpation, diagnostic imaging, and treatment including spinal manipulation. (J Manipulative Physiol Ther 2011;34:463-467)