Cervical spine: X-ray anatomy of the cervical spine

Considering the unique structure of the cervical spine (CS), the importance of the physiological functions it provides and the diversity of pathological processes, we considered it necessary to dwell in more detail on the anatomical and functional features and some variants of cervical spine pathology. Unfortunately, modern domestic literature on this issue is almost completely absent. In our opinion, this has been the reason for the recent sharp increase in the number of patients who are diagnosed with vertebrobasilar insufficiency either without sufficient grounds or without the necessary detailing. This leads to the prescription of the same type of therapeutic manipulations and drugs for pathological processes that differ in anatomical causes and pathogenetic mechanisms, which is hardly justified.

Taking into account the anatomy features, the cervical spine is divided into the craniovertebral zone, which includes the base of the skull and the two upper cervical vertebrae (in the literature it is designated as Oc-C1-C2), and the cervical spine itself C3-C7. The structure of the cervical spine is traditionally carried out on the basis of data from radiation methods - radiography, CT and MRI. We also note that the assessment of the parameters of the central section of the base of the skull and the craniovertebral zone, in our opinion, should be carried out primarily by neurosurgeons and neuropathologists, since the main complaints arising from the pathology of this zone are of a cerebral nature.

[ 1 ]

X-ray anatomy of the craniovertebral zone and cervical spine

The high complexity of the anatomical structure of the craniovertebral zone explains the need to identify the main radiographic landmarks used in its assessment.

On X-rays of the craniovertebral zone in the lateral projection, the relationships of the structures of the skull base to each other, as well as the relationships of the skull base to the upper cervical vertebrae are assessed. It is important to remember the fundamental condition for the correct assessment of the anatomical relationships in this zone: the X-rays must preserve images of all the necessary structures - the hard palate and perforated plate in the front, the occipital bone - in the back.

When assessing the central section of the base of the skull, the following indicators are analyzed:

• The sphenoidal angle (Fig. 58, a) is formed by the intersection of lines drawn tangent to the perforated plate (planum sphenoidale) and the Blumenbach's slope of the base of the brain. Normally, the value of the sphenoidal angle lies within the range from 90° to 130°;
• The angle of inclination of the foramen magnum (FM) (Fig. 58, b) is formed by the intersection of the line of entry into the FM (McRue's line) and the line connecting the posterior edge of the hard palate with the posterior edge of the FM (Chamberlen's line). Normally, the angle of inclination of the FM is from 0° to 18°.

On an X-ray of the skull in the anteroposterior projection, taken through the open mouth (“per os”), the ratio of the faces of the pyramids of the temporal bones is assessed; the lines tangent to them are normally on the same straight line or intersect at an angle that is open upward and is at least 160°.

The relationship of the skull (as a whole) with the spinal canal is assessed by the following indicators:

• The craniovertebral angle is formed by the intersection of lines tangent to the slope of the base of the brain and the posterior surface of the C2 vertebral dens. The angle characterizes the magnitude of the physiological craniovertebral kyphosis, which is normally 130°-165°.
• The sphenovertebral angle is formed by the intersection of lines tangent to the perforated plate (base of the anterior medullary fossa) and the posterior surface of the dens C of the vertebra. Normally, its value lies within the range of 80° to 105°.
• the Chamberlain index is determined by the distance between the apex of the C dentition of the vertebra and the line connecting the posterior edge of the hard palate with the posterior edge of the BZO (the so-called Chamberlain line). Normally, the Chamberlain line intersects the apex of the axis or is located within 3 mm above or below it;
• The MacGregor index is determined by the distance between the apex of the C2 dentition and the so-called basal line connecting the posterior edge of the hard palate with the occipital tubercle (the so-called Mae Gregor line). Normally, the Chamberlain and Mae Gregor lines coincide, or the Mae Gregor line is located 2-4 mm lower. Evaluation of the relationship between the foramen magnum and the cranial part of the spinal canal allows us to evaluate the stability of the craniovertebral zone. The following indicators are determined using a lateral radiograph (Fig. 58, 59): the angle of entry into the foramen magnum, formed by the intersection of a line tangent to the posterior surface of the C2 dentition and a line connecting the posteroinferior edge of the C body with the posterior edge of the foramen magnum. Normally, this angle is from 25° to 55°.

Craniovertebral distances:

• the anterior craniovertebral (syn. supradental) distance is measured between the anterior edge of the craniovertebral cavity (basion) and the apex of the C1 vertebral dens. Normally, the supradental distance is 4-6 mm in children and reaches 12 mm in adults;
• The posterior craniovertebral distance is measured between the upper surface of the posterior semi-arch of the atlas Q and the occipital bone. In the average position of the head, this indicator is normally 4-7 mm, but when tilted forward and backward, it can fluctuate from 0 to 13 mm;
• the ratio of the basion to the apex of the C2 vertebral dens: a perpendicular drawn from the basion to the line of entry into the spinal canal normally intersects the C2 dens;
• the ratio of the size of the entrance to the spinal canal to the full size of the foramen magnum (the ratio CB/AB) should normally be no less than 1/2, more often 3/4. The distance CB is estimated as the smallest distance "accessible" to the cranial part of the spinal cord - SAC (see abbreviations).

The main spondylometric parameters characterizing the anatomy of the cervical spine proper are assessed using lateral radiographs taken with the head in the average physiological position. The cervical spine is examined in functional positions of sagittal and lateral tilts to detect its hidden pathology, most often instability or hypermobility of individual vertebral-motor segments.

The retrodental distance is measured between the posterior surface of the C2 tooth and the anterior surface of the posterior half-arch of the C1 atlas. Normally, the retrodental distance should be equal to or exceed 2/3 of the distance between the internal contours of the anterior and posterior half-arches of C4; a decrease in this indicator is noted with atlantoaxial instability associated with instability of the anterior Cruveilhier joint.

The line connecting the posterior wall of the spinal canal between the C1 and C3 vertebrae is called the Swischuk line after the author who described it. Normally, the base of the spinous process of C2 should be located no more than 1 mm behind this line (the so-called Swischuk test). Violation of these relationships is characteristic of atlantoaxial instability associated with instability of the anterior Cruveilhier joint or with corporodental instability of C2.

The ratio of the sagittal size of the spinal canal, measured at the level of the C4 vertebral body, to the anteroposterior size of this body is described in foreign literature as the Pavlov index, and in domestic literature as the Tchaikovsky index. According to foreign data, this indicator should normally exceed 0.8, and its decrease indicates the presence of congenital stenosis of the cervical spinal canal. In domestic literature, a value of the index exceeding 1.0 is considered normal, with values from 0.8 to 1.0 the condition is considered compensated, and with a value of less than 0.8 - as decompensated stenosis of the spinal canal.

Among other indicators of the normal, physiological state of the cervical spine, the following should be highlighted:

• ossification nuclei of the apophyses of the cervical vertebrae appear at 10-12 years;
• the natural wedge shape of the cervical vertebrae is maintained for up to 10 years;
• the maximum retropharyngeal distance at the level of the C2-C4 vertebral bodies should not exceed 7 mm, at the level of the C5-C7 vertebrae - 20 mm;
• at the level of the C2-C3 segment in children, physiological mobility of the vertebrae is possible within the range from 0 to 3 mm, which is assessed as pseudo-instability of the specified segment;
• the fusion of the body and tooth C2 occurs, according to radiographic data, at the age of 3 to 6 years. However, on magnetic resonance imaging, the shadow of the corporo-dental synchondrosis is preserved at a much later date, including it can be detected in adults;
• the size of the Cruveilhier joint gap does not exceed 3-4 mm;
• the supradental distance is 4-6 mm in children and reaches 12 mm in adults;
• The ratio of the distance between the basion and the posterior half-arch of the atlas to the distance between the anterior arch of the atlas and the opisthion is described in the literature as the Power index, an indicator that characterizes the stability of the craniovertebral zone and is normally equal to or less than 1.0.