Background: Detailed study of the craniovertebral junction (CVJ) is necessary to completely understand the mechanism of its flexion and extension. Materials and methods: One cadaver head was sectioned in the sagittal plane. Also, in 22 volunteers, examined using the multislice computed tomography (MSCT), 14 parameters and 2 angles were measured in the neutral position, flexion and extension. Results: The obtained measurements showed the anterior part of the occiput to move inferiorly in flexion, and the anterior atlas arch and the tip of the dens to get closer to the basion. At the same time, the opisthion moves superiorly, but the cervical spine bends anteriorly. Consequently, the dens-opisthion diameter and the opisthion-posterior atlas arch distance slightly decrease in length, whilst the arches of the atlas (C1), axis (C2) and C3 vertebra become more distant. Following extension, the posterior part of the occiput moves inferiorly, so that the basion-dens tip, the basion-axis arch, and the basion-posterior atlas arch distances increase in length. In contrast, the distances of the C1–C3 arches decrease in length. The angle between the foramen magnum and the dens tip decreases 1.620 on average in flexion, but increases 3.230 on average in extension. The angle between the axis body and the opisthion also decreases in flexion (mean, 3.360) and increases in extension (mean, 6.570). Among the congenital anomalies, a partial agenesis of the posterior atlas arch was revealed (4.5%), as well as an anterior dehiscence of the C1 foramen transversarium (13.6%). Conclusions: The mentioned measurements improved our understanding of the CVJ biomechanics. The obtained data can be useful in the evaluation of the CVJ instability caused by trauma, congenital anomalies and certain spine diseases. (Folia Morphol 2017; 76, 1: 100–109)
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