Elsevier

The Spine Journal

Volume 10, Issue 3, March 2010, Pages 219-229
The Spine Journal

Basic Science
Comprehensive computed tomography assessment of the upper cervical anatomy: what is normal?

https://doi.org/10.1016/j.spinee.2009.12.021Get rights and content

Abstract

Background context

High-speed computed tomography (CT) exams have replaced traditional radiographs for assessment of cervical spine injuries in many emergency departments. Recent evidence demonstrates that even subtle displacements can indicate significant upper cervical spine injuries. Many different anatomical measurements have been described in the upper cervical spine to date, most of them based on X-ray. The range of anatomical relationships that exist in an uninjured population must be known to reliably detect abnormal relations. The measurements with the lowest normal variation are likely to be most useful in detecting injuries.

Purpose

The purpose of this study was to describe the normal quantitative anatomical relationships as well as the threshold measurements most likely to detect injury in the upper cervical spine.

Study design/Setting

Retrospective anatomical case review.

Patient sample

Seventy-six thin-sliced cervical CT scans randomly selected from a trauma population, all negative for injury in the cervical spine.

Methods

Forty-two different anatomical measurements were made of the upper cervical spine. These included traditional historical measurements and other detailed dimensions to characterize occipitocervical (OC) and atlantoaxial (AA) joint relationships.

Results

After review of all the anatomical measurements performed in the upper cervical spine, direct measurements of the joint space had the least variation. The mean OC joint space was 0.6 mm, with an upper 95% confidence interval (CI) of 1 mm at the most anterior or posterior aspects of the joints. This was true for both sagittal and coronal measurements. The mean AA joint space was 0.6 mm, with an upper 95% CI of 1.2 mm at the lateral aspect of the joint on the coronal image only. The midsagittal structures demonstrated significantly higher standard deviation and variability.

Conclusions

These results revealed consistently narrow joint spaces and left-right symmetry in the upper cervical spine joints that do not vary according to demographics. There was distinctly greater consistency in the coronal plane, which enabled more precise diagnostic measurement and side-to-side comparison of measurements. This precision will enable more accurate identification of abnormal scans, which should prompt consideration for additional workup. Thus, better understanding of these relationships may enable earlier detection of subtle craniocervical dissociative injuries based on CT scan data. This is important, because the only evidence of a severe injury on CT can be subtle misalignment.

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.

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