C1-C2 Vertebral artery

3D Model

Figure 4. A 3D model that was created by photogrammetry scan of C1 and C2 vertebrae and a vessel segment generated in Blender software v. 2.92 (Blender Foundation, Amsterdam, Holland). The suboccipital segment of the VA (V3) is the mobile portion of the VA. Depending on the head position it is stretched or compressed. Only, in neutral position, the vertical and horizontal portions of the V3 segment are perpendicular 1,2. When the head is rotated to contralateral side and extended (as required by the anterolateral approach) both portions of the V3 segment (horizontal and vertical) are stretched and run almost parallely, only separated by the groove of the posterior arch of the atlas 1,2. The degree of head rotation is the key during surgical positioning of the patient: a contralateral rotation less than 15° provides access to the anterior part of the cranio-vertebral junction, whereas rotation up to 30° brings the posterior arch into the surgical view