Morphometric study of the Axis vertebra

The axis (second cervical vertebra) is unique in possessing the dens or odontoid process and very specialized superior articular facets. The study was carried out to gather the metrical data of this atypical cervical vertebra. A hundred dried intact human axis vertebrae were measured using digital vernier caliper accurate up to 0.01 mm and a goniometer. Various linear and angular measurements of body, dens, lateral mass, pedicles, superior and inferior articular facets, lamina and spine were studied. The mean antero-posterior diameter of body of axis vertebra was 14.77 ± 1.73 mm. The external height of lateral mass on the right side was 8.77 ± 1.43 mm and 8.28 ± 1.26 mm on the left side. The height of dens was 14.86 ± 1.54 mm and the average transverse diameter was 9.28 mm. All the measurements, namely length, thickness and height of lamina were observed to be more on the right side than on the left, and all these differences were statistically significant. (P < 0.0001) The data in this study should be useful to surgeons while working around the second cervical vertebra to avoid injury to the vital structures.