We found 15 studies of modest methodologic quality that evaluated the diagnostic accuracy of the Canadian C-spine rule and NEXUS. We found that both rules had consistently high sensitivity, indicating that a negative test result is highly informative in excluding a clinically important cervical spine injury and, therefore, the need for radiographic examination. The value of a negative test result is further shown by the low negative likelihood ratio and post-test probability. In the only direct comparison, the Canadian C-spine rule had higher sensitivity, and thus gives fewer false negative results. Because both rules are based on imaging all patients with positive results, the low specificity and high false positive rate means that many people without injury will undergo unnecessary imaging. The results of the sensitivity analysis reinforced the primary findings. However, for the Canadian C-spine rule, the range over which specificity spanned was significantly reduced. This suggests that the diagnostic accuracy of the Canadian C-spine rule is superior when the rule is used in its entirety.
The findings of this review are consistent with a previous meta-analysis14
and 2 literature reviews.30,31
However, our review used a larger and more sensitive search strategy, which resulted in a larger number of primary studies identified for inclusion. In addition, we considered the methodologic quality of the included studies when interpreting the diagnostic accuracy. As a result, we have outlined an optimal diagnostic study design for future studies in this area (Appendix 2, available at www.cmaj.ca/lookup/suppl/doi:10.1503/cmaj.120675/-/DC1
) in order to reduce potential biases.
Clinically, our review highlights the effectiveness of the Canadian C-spine rule and NEXUS in clearing the cervical spine without the need for imaging, while maintaining patient safety. Although most of the studies included in this review are validation studies, only the Canadian C-Spine rule has been evaluated in an impact analysis study, which further supports its use in practice.21
Despite these findings, there is a more liberal use of imaging in current clinical practice, which may reflect patient preference, physicians’ fear of litigation or missing a fracture, or uncertainty of the application or accuracy of the screening tools. Improved education of physicians may facilitate greater use of these rules. In particular, educational content should focus on the subjective components of the Canadian C-spine rule (e.g., dangerous mechanism of injury,21
range of motion assessment) and NEXUS (e.g., distracting injuries, intoxication)32
because these components were most frequently misinterpreted.
Educating patients may also improve the utilization of these screening tools. In the absence of any clinical indication of a clinically important cervical spinal injury, routine imaging is not associated with psychological benefits or improved outcomes.33
Patients knowledge of this, together with knowledge about the accuracy of these screening tools weighed against the potential harms of unnecessary radiation exposure, would allow for more informed decisions to be made. To ease the concerns of patients discharged without imaging, further evaluation of alternate follow-up strategies, such as the 14-day proxy, would be beneficial for both clinical practice and research. Currently there is only limited data to support the use of the 14-day proxy as a reference standard,34
and there is no data on the accuracy of the 21-day surveillance strategy.
Limitations of this review included the selected use of data sources, the moderate methodologic quality of the included studies and the heterogeneity, which prevented pooling. Although a sensitive search strategy including citation tracking was used to identify eligible studies, we did not search for grey literature (e.g., contacting key authors to identify unpublished data). The inability to pool results means that the findings of this review are based on individual studies and only one direct comparison. Factors contributing to the heterogeneity identified included between trial variations in methodologic quality, clinical characteristics (e.g., professions applying the rules, their experience and training) and within-trial variations in how rules were interpreted and applied.
Based on studies with modest methodologic quality, we found that both the Canadian C-spine rule and NEXUS were highly sensitive rules that have the potential to reduce imaging rates. However, the lower specificity and false-positive results indicate that many people will continue to undergo unnecessary imaging. In the only direct comparison, the Canadian C-spine rule appeared to have better diagnostic accuracy, and it should be used over NEXUS to assess the need for cervical spine imaging. Future studies of diagnostic test accuracy need to ensure that rigorous methodologic procedures are followed to reduce bias. Furthermore, the evaluation of these tools in settings outside of emergency departments, in pediatric and older populations and by primary care physicians, such as general practitioners and physiotherapists, is also required.