Experimental Research And Clinical Application On The Cervical Spinal Canal Volume With Dynamic Three-dimension Spiral CT Measure

Objective:To measure cervical spinal canal volume under dynamic CT, and realize the dynamic change of the canal volume occupying ratio by herniated disc and tissue in three positions:hyperflexion, neutral and hyperextension, in normal adults and cervical spondylotic myelopathy (CSM) patients, and then probe its clinical significance.Methods:10 cases of normal and 20 cases of CSM scanned in hyperflexion, neutral and hyperextension positions under spiral CT(C₄～C₆). All the information was transferred to GE Advantage Workstation 4.2 for assessment. By using Volume Rendering (VR), Multiplanar Reformation(MPR) and Maximum Intensity Projection(MIP), with a reconstruction sheet thickness of 0.625mm, we measured the areas of both bony canal and fibrous canal in every chosen cross-sections and the sagittal diameters of cervical canal and cervical vertebra body. Then calculated the cervical spinal canal volume occupying ratio under the three positions using MATLAB 7.0.1, and statisticly analyzed the dynamic change.Results:1. There is significant difference of the cervical spinal canal volume occupying ratio in neural position between normal and CSM patients (P<0.01). 2. For those CSM patients, the cervical spinal canal ratio in neural position is in poor correlation with JOA score, it's Pearson coefficient correlation is 0.183(P>0.05). The secondary sagittal diameter of cervical spinal canal, the effective cervical spinal canal ratio and the cervical spinal canal volume occupying ratio are in good correlation with JOA score, and the Pearson coefficient correlation is 0.445(P<0.05), 0.496(P<0.05), -0.611(P<0.01), respectively.3. In different position, the dynamic change of the cervical spinal canal volume occupying ratio is coincidence between normal and CSM patients, the result is hyperextension>neutral>hyperflexion, and the differentiation is significant(P<0.01).Conclusion:1. The dynamic change of the cervical spinal canal volume occupying ratio calculated by spinal CT scan and image reconstruction, combined with MATLAB is an objective reflection of the dynamic change of pressure burden the cervical spinal cord bore in movement (flection and extention), and it has great significant in predicting the episode of CSM, estimating the degree of the compression to spinal cord, choosing a better surgical approach and avoiding some complications in operations.2. The secondary sagittal diameter of cervical spinal canal, the effective cervical spinal canal ratio and the cervical spinal canal volume occupying ratio are in good correlation with JOA score. And the latter has the better relativity, so it can be a quantitate index in the clinical diagnosis of CSM. As a volume assessment, it represents the effect of spinal stenosis on spinal cord in a 3D-structure other than a plane, which is more objective.3. The mechanism of spinal injury is that, in hyper-extention, the diameter of cervical spinal and the dural increases, added with the herniated intervertebral discs and the folding flaval ligaments, all of these factors make the cervical spinal canal volume occupying ratio increase dramatically. For the CSM patients with a decreased spare volume of canal, hyper-extention spinal injury is even easier to happen.4. In hyperflexion, the length of the cervical spinal canal increased, the herniated intervertebral discs recovered, added with the tightened thus thinner flaval ligaments and increased spinal spare volume, may be the compensate mechanism why the cervical curve is straightening up or even recurving in CSM patients. But hyperflexion is not a physiological position of cervical vertebrae, which is easy to cause biomechanics disorder of the cervical vertebrae, increase the degeneration rate of intervertebrae discs and facets. What's more, after the compensation broken, it will make the cervical spinal cord under severe pressure.