Preliminary CT study of C1-C2 rotational mobility in normal subjects

Abstract

IntroductionOnly in neutral position is the caudal surface of the atlas (C1) articular processes in full contact with its corresponding opposite in the axis (C2). Therefore, any rotational displacement of C1 on C2 should result in some degree of contact loss between the corresponding articular surfaces.The classical concepts about atlanto-axial (C1-C2) mechanics give a 40°rotation to both the left and right [29,30], so we can expect that a normal full rotation implies a wide articular surface contact loss. Nevertheless, not only is there no image representing this "expected fact" in classical literature, but it is simply indicated by means of circular arrows [30] upon an anatomical schematic model representing a lateral view of C1 on C2 in neutral position. White and Panjabi [30] show a contact loss between the opposing surfaces of the C1 and C2 articular processes (with no mention of it) when trying to demonstrate the possibly troublesome lengthening that the vertebral artery undergoes when nearing its rotational limits. Furthermore, we have also found a paper showing images in which the previously mentioned surface contact loss can be seen when explaining another altogether different topic [16].The paper by Fielding and Hawkins [8, 9] on atlantoaxial rotatory fixation has become a classic one and it is constantly referred to in almost all published papers relatAbstract A CT study of normal atlanto-axial (C1-C2) rotary mobility was carried out on ten normal immature subjects. In order to determine the limits of normality, the ten children underwent clinical and radiological examination. The clinical study included checking for objective signs of joint laxity and measurement of rotational neck mobility. The radiological study included standard lateral radiographs in neutral and maximal flexion positions and a CT scan taken in maximal left and right side rotation at the C1-C2 articular processes joint. The superpositioning of the images taken in every rotational direction showed, in all ten children, a wide contact loss between the C1-C2 corresponding facets, ranging from 74 to 85% of the total articular surface. The report on these images, carried out by three independent radiologists, concluded that there was a rotary subluxation in all cases. In the ten children studied, there were no significant differences with regard to neck mobility or laxity signs in clinical or standard X-ray examination. Our results lead us to conclude that, except for complete C1-C2 rotational dislocation with facet interlocking, a CT scan showing a wide -but incomplete -rotational facet displacement is not sufficient to define a status of subluxation. This leads us to perceive that there is a risk of overdiagnosis when evaluating upper cervical spine rotational problems in children. The concept of both rotary C1-C2 fixation and subluxation should be revised.

Variability of Upper Cervical Anatomy: A Reflection on Its Clinical Relevance

“…As demonstrated in several studies, the contact area between atlanto-axial joint surfaces during full rotational position may be as low as 15% in children [47] and 30% in adults [37]. The distances between the edges of the superior and inferior surfaces show mean values of 7.6 mm (˘0.8 mm) during full active axial rotation in adults [48].…”

“…A mean displacement of 0.5 mm (˘0.5) was reported considering only the impulse phase [49]. Compering these values with those from active rotation of the head [46,47,50], it is possible to assume that the inter-vertebral movement induced with such combined motion technique is not able to endanger vital structures such as the vertebral arteries and the spinal cord.…”

Atlantoaxial rotational dislocation and associated multiple-level fractures to the spine

“…This method has been presented by Rinaldi, in 1979 [18]. Villas et al have correlated the injury's severity to the joint's surface that remains uncovered during the dislocation [10,19,20].…”

Imaging of Atlanto-Occipital and Atlantoaxial Traumatic Injuries: What the Radiologist Needs to Know

“…■ Rotation as high as an average 79° was seen in one study of adult volunteers, and loss of contact of the articular facets of C1 and C2 during rotation as high as 74% -85%, seen in physiologic conditions, was seen in another (60). Therefore, diagnosis of subluxation of the atlanto-occipital joint should not be made based solely on the appearance of this joint at CT.…”