Variability of Upper Cervical Anatomy: A Reflection on Its Clinical Relevance

The upper cervical complex is a distinctive spinal area with a great need for mobility as well as stability. The specific anatomical morphology of the atlanto-occipital and of the atlanto-axial joints seems to support these complex functional demands. The present study reports on some systematic and non-systematic observations of specific morphological variations and variants of the upper cervical joint anatomy. They are reported with respect to morphological features of the transverse atlantal and alar ligaments, morphological features of the lateral atlanto-axial and atlanto-occipital joints, additional joint configurations of the atlanto-occipital junction, muscular attachments to the joint capsule of the lateral atlanto occipital joint, and the Processus styloideus in its relationship with movements of the upper cervical joints. The observations mainly confirm general anatomical descriptions from textbooks, although some confront with these basic anatomical configurations mainly due to large morphological variation. Additionally, specific anatomical variants may raise questions on the generally accepted functional anatomical features. Some of these specific morphological configurations may have major implications for the kinematics of the occipito-atlanto-axial complex. This paper intends to reflect on the functional impact of the observed upper cervical morphological variability.