The Atlas Vertebra Phenomenon

Force Distribution in the Atlas Region

In the upper cervical joint between the atlas (blue) and skull (pink), the intervertebral discs (gray), which normally act as shock absorbers between two vertebrae, are absent. Another remarkable feature is that the head does not rest on the atlas vertebra. Instead, the skull is held solely by the ligaments and muscular force of the atlas and neck muscles (red). It essentially "floats." From a biomechanical perspective, the atlas thus functions as a tension ring for the atlas muscles (red/green), distributing the shear forces (green/blue) across the first cervical vertebra in the horizontal plane. Si  multaneously, it acts as a gliding vertebra between the atlanto-occipital joints (pink/yellow/blue), preventing any pressure on the joint surfaces (yellow).

                                                                              Force distribution in the Atlas region according to Koerner

The deeper significance of this minor revelation for the treatment of head and neck pain is only gradually being recognized by the medical community. Furthermore, the long-term analysis of X-rays of the atlas region has shown that no significant osteoarthritis develops in the area of the atlanto-occipital joint. To support the head, the load-bearing capacity, shock absorption, shear forces, and mobility in the atlas region are managed and controlled solely by the muscles. The actual supporting function for the head, which can weigh up to five kilograms, is performed by the neck muscles and the circular muscles surrounding the atlas.

Another key functional function of the atlas region is ensuring the central blood supply to the brain via the vertebral artery. This paired cervical artery originates in the thoracic cavity and then runs to the right and left through the foramina of the transverse processes of the cervical vertebrae to the skull. At the first cervical vertebra, the atlas, both cervical arteries curve around the posterior part of the vertebral arch and enter the cranial cavity there.

To ensure adequate blood supply despite the high mobility of the atlas region, the neural control receptors of the atlas ring muscles are closely connected to the vessel walls of the two sharply angled internal arteries.
Impaired blood flow in this region can lead to disorders such as dizziness, which is very often triggered by rapid head movements. Furthermore, occipital headaches, tinnitus, hearing loss, visual disturbances, peripheral sensory disturbances in the upper extremities, gait instability, and temporary speech disorders can occur.