Establishment of the Lunar Phase Morphological Classification for Cervical Spinal Canal

Study Design Retrospective clinical trial. Purpose To establish a morphological classification of the cervical spinal canal using its parameters. Overview of Literature Cervical spine computed tomography (CT) data of 200 healthy volunteers in 2 years were analyzed. The morphology of the spinal cord was also analyzed. Methods The median sagittal diameter and transverse diameter of the spinal canal from C2 to C7 were measured on CT images. The ratio of the median sagittal diameter to the transverse diameter was calculated. Accordingly, the spinal canal shape of each segment was classified into four, and the specific criteria of lunar phase classification were determined through linear discriminant analysis based on the ratio of the median sagittal diameter to the transverse diameter. The inter-rater reliability of the classification was explored using Kappa coefficients. Finally, the morphology of the different segments of the cervical spinal canal in healthy volunteers was revised and compared. Results According to the ratio of the median sagittal diameter and the transverse diameter of the cervical spinal canal, the lunar phase classification of the cervical bony spinal canal was determined as follows: full-moon >0.65, 0.55< convex-moon ≤0.65, 0.46≤ quarter-moon ≤0.55, and residual-moon 0.05). The frequency of the spinal canal of the residual-moon type was the highest, and the full-moon (6.5%) and residual-moon (7.5%) types of C7 were rare. Conclusions The morphological classification of the cervical spinal canal was established to present anatomical variations. The classification showed good inter-rater reliability.