Basic ScienceComprehensive computed tomography assessment of the upper cervical anatomy: what is normal?
Introduction
Traumatic occipitocervical (OC) injuries, including damage to the OC and atlantoaxial (AA) articulations, are common findings in fatal cervical spine injuries [1], [2], [3], [4]. In an OC injury, the primary ligamentous stabilizers of the cervical spine are frequently severely damaged [5], [6], [7], [8], [9], [10], [11]. The worst of these can be described as internal decapitation [8]. Early recognition of these injuries and appropriate management and stabilization are associated with improved outcomes [8], [12], [13]. Traditional diagnostic methods for evaluating the upper cervical spine have been based on relationships of the skull with the cervical spine as visualized from lateral radiographs [14], [15]. These measurements have focused on midsagittal structures, including the posterior cortical margin of the axis body, the basion, and the posterior AA ligament. These methods have limited sensitivity and specificity for detecting injury workup [16], [17], [18]. Additionally, given the distance between the structures, measurements may change with the incident angle of the X-ray beam (rotational distortion) and the distance between the target and the X-ray film because of parallax error [19], [20], [21].
For reasons related to superior qualitative analysis of bone and its relationships, the use of computed tomography (CT) scan for the trauma evaluation of the spine has gained substantial popularity [22], [23]. Some studies are available that describe and quantify upper cervical alignment, particularly regarding the occipitoatlantal interval [17] or the condylar gap [24], [25], [26], as measured in the sagittal plane. However, despite increased use of CT imaging, specific criteria that can identify normal and abnormal CT anatomy in the upper cervical spine are not well defined [24], [27], [28]. Thus, the purpose of this study was to detail the normal anatomical features and relationships of the upper cervical spine as seen on the CT scan. In turn, this improved understanding should establish better criteria for detecting subtle upper cervical abnormalities or injury.
Section snippets
Patients
The patient population consisted of 100 patients who underwent a screening multidirectional CT scan of the cervical spine with multiplanar reconstructions as part of a trauma protocol between November 2006 and September 2007. Patients were randomly selected by searching both the trauma registry and the radiology teaching file databases. Patient demographics, including age, sex, and injury mechanism, were obtained from the medical record, and associated injuries were documented. All scans were
Results
The characteristics of the study population are described in Table 4. Based on multivariate analysis of variance, there was no evidence of significant variations associated with age, race, or gender for any of the measurements performed.
Almost all of the measurements were not normally distributed with statistically significant skewness (p<.05). Examination of the histograms of the data distribution revealed that the data were skewed toward the lower range of data, with a tail toward the higher
Discussion
This study has shown that, in general, the upper cervical spine has reliable left-right symmetry and consistently narrow joint spaces. Of all the midline and paramedian measurements, the congruency of the OC joints was found to be most consistent. These are represented by P1, P2, and P3 in Fig. 2 and C1, C2, and C3 in Fig. 3. Occipitocervical joint measurements were more consistent than the AA joints. At the OC joint, there was exceptional symmetry from right to left in both the coronal and
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Author disclosures: JAH (stock ownership, including options and warrants, Medical Metrics, Inc., other office, Medical Metrics, Inc.; grants, DARPA).
A research fellowship grant from Medtronic provided salary support for the research fellow (ND) and is gratefully acknowledged.