स्पाइन जर्नल

Morphometric Analysis of Human Second Cervical Vertebrae (Axis)

Abstract

Teo EC, Haiblikova S, Winkelstein B, Welch W, Holsgrove T and Cazzola D

Possessing an odontoid process and unique superior articular facets, the axis vertebra morphometry significantly differs from morphometry of other cervical vertebrae. The fractures of axis, especially its dens, are very common and surgeries highly risky. Knowledge of the axis dimensions is essential not only for preclinical studies, diagnosis of spinal cord diseases, planning of the surgeries but also for correct selection and insertion of surgical instruments or vertebral implants design. Many quantitative studies of the second cervical vertebra have been performed, yet still lacking the area parameters determination and precision of three-dimension in vivo measurement. Vertebral dimensions are reported to vary among populations, although there are very little studies examining Caucasian specimen.

This study aims to provide three-dimensional in vivo morphometric analysis of the axis vertebra as well as comparison to the previous studies. The clinically relevant vertebral dimensions were measured on the threedimensional model reconstruction of CT scans providing high accuracy. Five human second cervical vertebrae were investigated (Caucasian males) and linear, area and angular dimensions were measured.

The data on vertebral body dimensions were best fitting Doherty and Naderi measurement. The vertebra body anterior height was established to be 26.2 mm and the posterior height 21.4 mm. The dens parameters were similar to those presented by Doherty. Doherty also reported large variation in the dens sagittal angle which was observed in the present study as well. The dens height was determined to be 17.8 mm which is significantly greater compared to the previous studies. The smallest height among specimens was reported to be 17.0 mm. The smallest anteroposterior or transverse diameter of the dens measured was the upper depth, 9.4 mm. The smallest and biggest areas of dens were measured to be 79.0 mm2 and 121.6 mm2. The superior articular facet area with mean value 211.2 mm2 was observed to be significantly bigger than the inferior area, 141.2 mm2. The mean sagittal angle of the inferior facet area was assessed to be 42.1° and the mean frontal angle of the superior articular facet 69.3°. The parameters of articular facets measured by Xu correspond to the present study. Due to the vertebral body enlargement in the inferior part of vertebra, the spinal canal superior depth,18.0 mm, was observed to be bigger than its inferior depth, 16.2 mm. In case of the spinal canal depth, Sengul measured values considerably greater than other studies. However, Singla, Gosavi and Xu presented the parameters very similar to the present study. Spinal canal width was measured to be 24.4 mm supporting the measurement done by Sengul which is 24.7 mm.

The measured vertebral dimensions can be used either for development of instrumentation, preclinical planning of surgeries, implant design or as the reference values for evaluation and diagnosis of various clinical conditions.