Disc-level canal diameter predicts risk of spinal cord injury after minor trauma

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A study published in The Spine Journal indicated that patients with a disc-level spinal canal diameter below 8mm, on MRI, are at increased risk of acute spinal cord injury following a minor trauma to the cervical spine.

Study authors Nikolaus Aebli, Orthopaedics and Spinal Surgery, Swiss Paraplegic Centre, Nottwil, Switzerland, and others reported that following a minor trauma to the cervical spine, some patients may develop acute spinal cord injury. They added that the presence of spinal stenosis (either because of a congenitally narrow spinal canal or degenerative changes) may increase the risk of spinal cord injury after this type of trauma, but reported that current methods of assessing the presence of spinal stenosis are limited. For example, the Torg-Pavlov ratio (the cervical spinal canal to vertebral body ratio) on radiographs has a low predictive value and canal narrowing caused by soft tissue cannot be assessed on conventional radiographs. 


However, Aebli et al commented that MRI parameters could be used to predict the risk and severity of acute spinal cord injury after minor trauma. They reported: “The aim of the present study was therefore to investigate the spinal canal diameter and the space available for the cord at the level of the intervertebral disc in patients suffering from acute cervical spinal cord injury after a minor trauma to the cervical spine.” The authors explained that they had two hypotheses: that the disc-level spinal canal diameter and space available for the cord was significantly smaller in patients with spinal cord injury after a minor trauma compared with patients without neurologic  injury after this type of trauma, and significantly decreased disc-level spinal canal diameter and space available for the cord would be associated with increasing severity of spinal cord injury.


In the study, of patients who had received a minor trauma to the cervical spine, 52 had an acute cervical spinal cord injury and 131 did not (the control group). Using MRI, Aebli et al assessed the sagittal diameter of the vertebral body, the sagittal outer diameter of the subarachnoid space at the midpoint of the vertebra (midvertebral canal diameter), the sagittal outer diameter of the subarachnoid space at the level of the intervertebral disc (disc-level canal diameter), and the sagittal diameter of the spinal cord at levels C2 and T1. 


They found that in all parameters, there were significant differences between patients with spinal cord injury and those without spinal cord injury (p<0.01)—stating: “A cutoff value of 8mm for the minimal disc-level canal diameter provided the greatest proportion of true positives (positive predictive value of 84%) for predicting the risk of spinal cord injury after a minor trauma to the cervical spine.” Therefore, their hypothesis that patients with spinal cord injury would have a reduced disc-level space diameter and space available for the cord compared with non-injured patients was validated.
However, their hypothesis that the disc-level spinal canal diameter and the space available for the cord would be significantly decreased with increasing spinal cord injury was not proven. Aebli et al did not find any significant differences in MRI parameters between patients with different grades of spinal cord injury severity.


The authors concluded: “Patients at risk of acute spinal cord injury after a minor trauma to the cervical spine can be identified by applying a disc-level canal diameter cutoff value of 8mm.” They added that additional factors, such as trauma mechanism, to the radiological characteristics of the cervical spinal canal affected the severity of acute spinal cord injury after a minor trauma to the cervical spine.


Aebli told Spinal News International: “As a spinal specialist, I am lacking reliable parameters for identifying critical cervical spinal canal stenosis in my patients and for assessing their risk of spinal cord injury after a minor trauma. The disc-level canal diameter cutoff value provides a valuable additional information for deciding on further diagnostic and therapeutic steps or for making recommendations on life style changes (eg. whether to participate in contact sports or not) in these patients.”

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