Quantitative Anatomy of the Second Cervical Vertebra

STUDY DESIGN: While the gross anatomy of the second cervical vertebra has been well described qualitatively, our evolving understanding of spinal pathology makes it necessary for the modern surgeon to have more quantitative information. OBJECTIVES: The authors' goal was to directly measure clinically relevant dimensions of the second cervical vertebra, using a collection of anatomic specimens. SUMMARY OF BACKGROUND DATA: Many existing studies have been based on analysis of radiographic images, which are subject to errors of magnification, rotation, and projection. Several recent studies of dens morphology have been based on direct measurements. These studies in general did not extend to the lateral masses or posterior ring, however. METHODS: Direct measurements using digital calipers and goniometer were taken from 51 dried human second cervical vertebrae. The maximum and minimum anteroposterior and lateral diameters of the dens, and the anteroposterior and lateral diameters of the end-plate and foramen and were measured. The heights of the dens and superior facet surfaces were measured relative to a plane defined by the anterior-most point of the inferior endplate and the inferior-most points of the inferior facet surfaces. RESULTS: The greatest variation was found in the dens angle, with specimen dens angles ranging from -2 degrees to 42 degrees. The most significant correlations were between the total height of the vertebra and the height to the base of the dens (r2 = 0.81), between the total height of the vertebra and the maximum lateral diameter of the dens (r2 = 0.77), and between the minimum lateral diameter of the dens and the maximum lateral diameter of the dens (r2 = 0.63). CONCLUSIONS: The dimensions measured in this study confirm a significant degree of anatomic variation in the second cervical vertebra, and show no important correlations among the various measured dimensions. In particular, no significant correlation was found between dens height and canal diameter. Dens angle in the sagittal plane was the most variable measurement.