In the newborn and young infant the vertebral bodies, although basically rectangular, often appear more oval because they have rounded corners, especially anteriorly (Fig. 2.1a). Thereafter the vertebral bodies become more cuboid-rectangular (Fig. 2.1b), but in some individuals can appear exceptionally flat (Fig. 2.1c). The latter configuration is not to be misinterpreted as being representative of platyspondyly, as seen with bony dysplasias, for it merely reflects the wide spectrum of the normal appearance of the vertebral bodies.

In the normal individual the neural arch of C2 usually is the largest such structure in the upper cervical spine. This is helpful when one is assessing radiographs for the presence of occipitalization. With occipitalization, C1 is fused to the base of the skull and yields to C2 as being the uppermost visualized posterior arch. Ordinarily it would be the second arch to be visualized. The posterior arch of C1 is smaller than the posterior arch of C2 and thus, when this arrangement is altered, and the uppermost visualized neural arch is the largest one present, one should suspect occipitalization.

In addition to the preceding considerations, the neural arches and spinous processes of the cervical vertebrae can show even more variation in configuration. In this regard, some may be hypoplastic, and in addition, while normal spinous processes tend to point downward, occasionally they point upward. Because of this they may erroneously suggest that a pathologic increase in the intraspinous distance is present (Fig. 2.2).

Finally, because of the complicated embryonic development of the cervico-occipital junction, aberrant bony ossicles frequently are encountered in the upper cervical spine and at the base of the skull. Most of these occur anteriorly, but they also can be seen posteriorly, and at either site usually are round or oval. Such ossicles have smooth edges and should not be misinterpreted for avulsion fractures (Fig. 2.3).

In most individuals, flexion or extension of the cervical spine results in little excess motion. However, in other instances, and especially in infants and young children, since the ligaments are lax, normal physiologic hypermobility is more common and leads to spinal configurations that frequently are confused with pathologic states [1]. In addition, it is important to appreciate that the apex of the flexed cervical spine curve in infants and young children is located at a different level from that in older children and adults [2]. In infants and young children it is located in the upper cervical spine at approximately the level of C2–C3 (Fig. 2.4a), while in older children and adults it is located in the midcervical spine, that is, somewhere between C4 and C6 (Fig. 2.4b). This explains why cervical spine injuries, primarily flexion induced, are more common in the upper cervical spine in infants and young children, and more common at the C4–C6 level in older children, adolescents, and adults. This also is probably why degenerative changes in adults occur primarily at the C4–C6 level. In addition, when considered with the overall increased mobility of the infant’s and young child’s spine, it is more readily understood why so many normal hypermobility phenomena occur in the upper cervical spine in this age group.

This finding is common in young infants during hyperextension of the cervical spine [1]. The resultant configuration is that of a very high, indeed dislocated appearing, anterior arch of C1 (Fig. 2.5). The finding, to the uninitiated can be quite alarming but, is entirely normal.

Similar to hypermobility of the anterior arch of C1, hypermobility of C1 with flexion can result in an exaggerated intraspinous distance between C1 and C2 [1]. However, as opposed to the high anterior arch of C1 phenomenon, this configuration also can be seen in older children. Indeed, distances of up to 10 or even 12 mm can be encountered and still be normal (Fig. 2.6). In these cases, however, the C1–dens distance (predental distance) is normal.

It is well known that the predental distance in infants and young children can be wider than in adults. Indeed, up to 5 % of normal individuals can demonstrate a predental distance of 5 mm, but most often the distance is somewhere between 2 and 3 mm on initial, neutral cervical spine studies [3, 4]. In any of these cases, if there is no increase in the predental distance on flexion, the finding can be considered normal (Fig. 2.7). However, it also should be recalled that with flexion there can be a normal increase in the distance of up to 2 mm (Fig. 2.8). If there is more widening than this, one should suspect underlying instability of the ligaments, either on a traumatic or congenital basis. The latter problem is associated with anomalies of the dens, primarily dens hypoplasia and an associated os odontoideum.

Physiologic posterior dislocation of the vertebral bodies occurs less frequently than anterior dislocation. It tends to occur over the midcervical spine, and maximum normal sliding should be no more than 2 mm [5]. The displacement can occur at one or multiple levels (Fig. 2.9).

With spasm, or rigid positioning on an “EMS transporting backboard,” a patient’s head can be cocked forward so that angulation of C2 on C3 results [1]. In such cases there is no actual anterior displacement of C2 on C3, but the severe degree of angulation encountered can erroneously suggest that the ligaments between C2 and C3 have been disrupted and that dislocation is present (Fig. 2.10a). In these cases I have found it helpful to draw a line along the posterior aspect of C2 and the dens and note whether it intersects or just touches the upper posterior corner of C3. If it does, no dislocation is present (Fig. 2.10b). In such cases the posterior cervical line [6] should not be applied, for it will lead to erroneous conclusions. The line was designed to be used only if anterior displacement of the body of C2 on C3 was present (see next section).

Anterior dislocation of C2 on C3 can occur with a hangman’s fracture, but in infants and children it is far more common on a normal, physiologic basis [6, 7]. The degree of displacement is usually no more than 2 mm, but to the uninitiated a traumatic dislocation often is at first suggested (Fig. 2.11). In these cases I have found it helpful to apply a line, the posterior cervical line [6], to the anterior cortices of the spinous tips of C1 and C3, and then note whether it intersects, touches, or comes close to the anterior cortex of the spinous tip of C2 (Fig. 2.12). If the line misses the anterior cortex of C2 by more than 1.5 mm, a hangman’s fracture should be suspected. Otherwise, the finding should be considered physiologic (Fig. 2.13).

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