Shape change in the atlas with congenital midline nonunion of its posterior arch: a morphometric geometric study

Publication date: Available online 29 May 2017
Source:The Spine Journal
Author(s): Luis Ríos, Carlos Palancar, Francisco Pastor, Susana Llidó, Juan Alberto Sanchís-Gimeno, Markus Bastir
Background contextcongenital midline nonunion of the posterior arch of the atlas is a developmental variant present at a frequency ranging from 0.7% to 3.9%. Most of the reported cases correspond to incidental findings during routine medical examination. In cases of posterior nonunion, hypertrophy of the anterior arch and cortical bone thickening of the posterior arches have been observed, interpreted as adaptive responses of the atlas to increased mechanical stress.Purposewe sought to determine if congenital nonunion of the posterior arch results in a change of the shape of the atlas.Study Design/SettingAnalysis of first cervical vertebrae from osteological collections through morphometric geometric techniques.Methodsa total of 21 vertebrae were scanned with a high-resolution 3D scanner (Artec Space Spider). To capture vertebral shape, 19 landmarks and 100 semi- landmarks were placed on the vertebrae. Procrustes superimposition was applied to obtain size and shape data (MorphoJ), which were analyzed through Principal Component Analysis (PCA) and mean shape comparisons.Resultsthe PCA resulted in two components explaining 22.32% and 18.8% of total shape variance. The graphical plotting of both components indicates a clear shape difference between control atlas and atlas with posterior nonunion. This observation was supported by statistically significant differences in mean shape comparisons between both types of vertebra (p<0.0001). Changes in shape are observed in the superior and inferior articular facets, the transverse processes and the neural canal between control and nonunion vertebrae.Conclusionsnonunion of the posterior arch of the atlas is associated to significant changes in the shape of the vertebra.



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