The atlantooccipital joint is the name given to the upper cervical joint. Together with the lower upper cervical joint, it provides mobility similar to that of a ball and socket joint.
What is the atlantooccipital joint?
The atlantooccipital joint is also known as the upper cervical joint or articulatio atlantooccipitalis. This refers to the joint located between the occipital bone (Os occipitale) and the first cervical vertebra (Atlas). Together with the atlantoaxial joint (lower cervical joint) and the muscular attachments, it provides a connection between the base of the skull and the cervical spine. In addition, it forms a significant integration region within the human body. The mobility of the atlantooccipital joint resembles a ball and socket joint.
Anatomy and structure
The atlantooccipital joint is an egg yolk joint (ellipsoid joint). It is located between the two occipital condyles and the fovea articularis of the 1st cervical vertebra. The joint capsule of the upper cervical joint is reinforced on the ventral side and the posterior side. In the section of the back of the membrane, a larger hole is located between the cervical vertebrae, which is closed only by this membrane. From this area, the subarachnoid space or the cisterna cerebellomedularis, which is its extension, can be accessed through the use of a cannula. In this way, a puncture of cerebrospinal fluid (CSF) is performed. At this point, however, the spinal cord can also be destroyed by a sharp puncture. Within the spinal canal is the membrana tectoria, a ligament that runs across the two upper cervical joints. Below this is the cruciform ligament of the 1st cervical vertebra (ligamentum cruciforme atlantis). Also of importance to the atlantooccipital joint is the atlantoaxial joint. This consists of the articulatio atlantoaxialis mediana and the articulatio atlantoaxialis lateralis. The 1st and 2nd cervical vertebrae (axis) are connected to each other by the upper joint sections of the articular processes. The two joint areas are enclosed by a common joint capsule. Several ligaments provide fixation. The dens axis, a cone-shaped bony process, is responsible for rotational movements of the head such as head shaking. The cone joint allows rotation of 20 to 30 degrees to either side. Thus, the inferior cervical joint is responsible for about 70 percent of head rotation. The fibrous tracts of the joint capsule that stabilize the atlantooccipital joint reinforce dorsally and ventrally in a ligamentous fashion. They bear the names Ligamentum atlantooccipitale anterius and Ligamentum atlantooccipitale posterius. Further stabilization is provided by the ligamentum cruciforme atlantis.
Function and Tasks
The interaction of the atlantooccipital joint and the atlantoaxial joint provide fine gradation of head movements. Through the upper cephalic joint, a forward tilt of the head by 20 degrees as well as a backward tilt by 30 degrees is feasible. In addition, it can tilt the head 15 degrees to the side. In this way, the atlantooccipital joint allows for flexion and extension of the head. Combinations of nodding movements of the upper upper cervical joint and rotating movements of the lower upper cervical joint ensure movements to all three spatial planes. Furthermore, the atlantooccipital joint, together with the atlantoaxial joint as well as the muscular attachments, provides a connection between the base of the skull and the cervical spine.
Diseases
Various injuries can affect the atlantooccipital joint. For example, there is a risk of crushing or even severing the spinal cord and medulla oblongata (medulla oblongata) due to a neck fracture. This results in a fracture of the tooth of the 2nd cervical vertebra. Likewise, rupture of the ligaments of the dens axis is possible. This in turn results in severe damage to the respiratory and circulatory center, which immediately leads to the death of the affected person. If the dens axis is suspected to be ruptured in an injured person without spontaneous breathing, vital intubation must be performed to counteract possible damage to the spinal cord or the medulla oblongata. This must be done with the cervical spine in a neutral position. Ligamentous injuries that do not involve a fracture of the dens axis may result in instability of both upper cervical joints. This includes symptoms such as breathing disorders or central sleep apnea.If the dens axis is only incompletely formed or even not formed at all, this is considered to be the cause of an atlantoaxial subluxation. In this case, the upper cervical joint between the 1st and 2nd cervical vertebrae is incompletely dislocated. There is a risk of spinal cord damage because of this. Another possible injury to the upper upper cervical joint is a tear of the retaining ligament located between the 1st cervical vertebra and dens axis. Often, the joint capsule parts between the 1st and 2nd cervical vertebrae are also damaged. The atlas therefore threatens to drift onto the axis. Doctors then speak of an atlantoaxial instability injury. Pronounced instability of the two upper cervical joints is also possible in the case of tears in the joint capsule between the wing ligaments or atlas and occipital bone. It is not uncommon for physicians to overlook instability impairments in their diagnosis because the patient tends to tense muscles more than instability during the examination. The reason for this is the increased tension of the muscles, which is a protective device against vertebral drift. However, visualization of the loss of stabilization of the upper cervical joint is possible by fluoroscopy after administration of muscle relaxants. The symptoms of instability injury are mainly due to circulatory disturbances in the region of the internal carotid artery, jugular veins and vertebral arteries. Repeatedly, a lack of oxygen can occur because of this. In addition, affected individuals often suffer from visual disturbances such as flying gnats, dizziness and lightheadedness. However, infarction does not occur. Instead, a mildly pronounced cell death of the brain parenchyma occurs.
