Cervical Vertebrae
This article focuses on the typical cervical vertebrae (C3-C7)
Regions
The typical cervical vertebrae are C3 to C7. The transition zone is centred on C2, and so the upper transition zone refers to the atlantoaxial joint, and the lower transition zone refers to the C2-C3 joint. The suboccipital zone is centred on C1.
The cervical spine can also be divided into the upper occipito-atlanto-axial joint complex, and the sub-axial spine.
- Upper occipito-atlanto-axial joint complex
- Multiple synovial joints with strong transverse and alar ligaments provide about half of total movements
- Movements: C0-1 - nutation, C1-2 - rotation
- Nerve roots: C1 nerve sits under the vertebral artery, C2 nerve root sits with veins.
- They are well preserved in older subjects
- Sub-axial spine; discs, and zygapophyseal joints.
- Uncovertebral clefts
- 45 degree facet joints, allows for flexion and extension but not much rotation
- Oblique, antero-lateral course of nerve roots
- Vertebral arteries in foramina transversaria.
- Small anterior muscles, large posterior muscles. Therefore vulnerable to extension trauma.
Suboccipital Zone
- Main article: Atlanto-occipital Joint
Transition Zone
Upper Transition Zone
- Main article: Atlanto-axial Joint
Lower Transition Zone
The lower half of the axis (C2) vertebra has a typical cervical vertebra structure. There is a vertebral body centrally, and paired inferior articular processes laterally. The upper half receives the paired lateral masses of the atlas (C1), and the load is transmitted down the cervical spine through an anterior channel (vertebral bodies) and a posterior channel (the paired zygapophyseal joints). The load is approximately split equally between these two channels.
Typical Cervical Vertebrae
The typical cervical consists of a vertebral body and paired articular pillars. There are also transverse processes that come outwards from the articular pillars. The laminae are formed posteriorly by two pillars, and there is a spinous process in the middle. The transverse and spinous processes are essentially levers that muscles act through in order to alter the position of the cervical vertebrae.
Each vertebral body has paired uncinate processes that sit along their superolateral margins. They are positioned more anteriorly in the upper cervical spine, and more posteriorly in the lower cervical spine. The uncovertebral or Luschka joint is the joint that is formed by the uncinate process and the inferolateral portion of the vertebral body above. The uncinate processes limit lateral flexion maintaining the integrity of the ipsilateral intervertebral foramen, and also maintain the position of the intervertebral discs with axial rotation.
Adjacent articular pillars are joined by the zygapophysial joints. These are synovial joints that are formed by the inferior articular process of the vertebra above with the superior articular process of the vertebra below. The joints have meniscoids between them made up of fibroadipose tissue. The joints are planar and face backwards and upwards, or more descriptively they are typically oriented about 40° to the coronal and transverse planes. The C2-3 joint is exception, with the joints also facing medially, forming an ellipsoid socket where the axis (C2) sits.
Cervical intervertebral discs are located anteriorly between adjacent vertebral bodies, and have a fundamentally different structure to lumbar intervertebral discs. The discs are fibrocartilaginous in the adult, and there is effectively no posterior annulus. The posterior aspect of the disc forms a normal physiological cleft by around the age of 30, which acts as a joint space.
The anterior longitudinal ligament only connects the typical vertebra, extending from C2 caudally. The posterior longitudinal ligament is found on the floor of the vertebral canal of the typical cervical vertebrae. At the atlantoaxial region it expands to form the membrana tectoria, separating the dural sac and spinal cord from the median atlantoaxial joint.
The vertebral bodies have a saddle joint shape. The superior surface of each vertebral body has two curvatures. One curvature is slightly convex along the sagittal plan. A second curvature is deep concave in the transverse plane between the uncinate processes. With this saddle shape, motion is restricted to two planes, the sagittal and oblique coronal planes.
In the sagittal plane, the vertebral bodies are able to rotate and translate to allow for flexion and extension. The axes of rotation are at different locations down the spine. In the upper spine the axis of rotation is below the moving vertebra, but the axes move progressively closer to the disc down the cervical spine.
In the oblique coronal plane, set at 40° forward of the coronal plane in the same plane of the zygapophysial joints, the vertebra can rotate. The vertebra is like an inverted cone with a fixed apex, but with a base that can rotate. The apex is the anterior, median point on the vertebral body: the location where the anulus fibrosus fibres point towards, and in doing so these fibres fix this point in place. The base is the ellipsoid joint formed by the inferior edge of the upper vertebral body, and the uncinate process of the lower vertebral body. The base of the cone thus is able to swing across the ellipsoid surface. The zygapophysial joints display a sliding motion during this movement, with the inferior articular processes sliding laterally under the superior articular processes.
