Reliability and reproducibility of measurements in para-sagittal planes on sub-axial cervical vertebral bodies: a morphometric study of endplates in three-dimensional models

BACKGROUND: Dimensional measurements have been implemented on a variety of entities in morphological studies of the sub-axial cervical vertebral endplate. Despite great progress, little information between the mid-sagittal plane and bilateral uncinate processes has been acquired due to the lack of a reliable method to determine the para-sagittal planes. Also, few studies of this region are available. We proposed a new approach to defining the para-sagittal planes on a 3D cervical vertebral body model; in this approach, dimensions can be measured in a specific plane. The aim of this study was to assess the inter-observer and intra-observer reliability of the measurements in different sagittal planes on sub-axial cervical vertebral endplates of 3D models. METHODS: We established mid-sagittal and bilateral quarter para-sagittal planes on the 3D model of a sub-axial cervical vertebral body based on landmarks labeled on the surface. By intersecting the vertebral body with the planes, three curves located at the three para-sagittal planes were generated. Linear dimensions were measured on every curve by two observers separately, and in total, 24 sub-axial cervical spines were included in the study. The first observer (O1) performed the procedure twice with an interval of 2 weeks. The paired t test, Wilcoxon matched-pairs signed-rank test and the interclass correlation coefficient (ICC) were employed to evaluate the inter- and intra-observer reliability of the proposed method. RESULTS: There were no significant differences in most intra- and inter-observer comparisons, and higher non-significant proportions were found in the intra-observer comparisons than in comparisons between different observers. The interclass correlation coefficients (ICCs) in the measurements were excellent (> 0.75) in most circumstances, and the values in intra-observer comparisons were higher than those in inter-observer comparisons. CONCLUSIONS: In this study, we proposed an approach to determine the bilateral quarter para-sagittal planes in a 3D cervical vertebral body model; the results demonstrated that the method is reproducible with high intra- and inter-observer agreement.