A Morphometric Study of the Adult Human Axis Vertebra and its Clinical Implications

Abstract

Introduction: The axis (second cervical vertebra) is unique in possessing a dens or odontoid process and a specialised superior articular facet. It acts as an axle for the rotation of the atlas and the head around the strong dens which project cranially from the superior surface of the body. A good understanding of the dimensions of this bone is necessary for the evaluation of many clinical problems. Objectives: 1. To measure various parameters of the axis vertebra. 2. To compare the results with the previous studies. Materials and Methods: This observational study was carried out on 100 dried human vertebrae of unknown sex used for teaching in the Department of Anatomy at Madras Medical College. The parameters were measured by a digital vernier calliper and an inch tape. Results: The mean pedicle length on the right and left sides were 28.7mm and 27.8mm, the mean pedicle width on the right and left sides were 8.1mm and 8.3±1.61mm, and the mean pedicle height on the right and left sides were 9.4±1.54 mm and 9.4±1.34mm. The mean anteroposterior diameter of the superior articular facet on the right and left sides was 16.53±1.44mm and 16.62±1.52mm. The mean transverse diameter of the superior articular facet on the right and left side was 14.42 ±1.48mm and 14.62±1.68mm. The mean anteroposterior diameter of the inlet and outlet of the vertebral canal was 20.9±2.09mm and 18.23±2.32mm. The mean transverse diameter of the inlet and outlet of the vertebral canal was 20.4±1.89 and 20.2mm. The mean height and width of the dens are 15.4±1.77 and 10.05±0.91. Conclusion: Anatomical knowledge of accurate dimensions of the axis vertebra is required for evaluation of many surgical problems in the craniovertebral junction. Correction of instability of the atlanto– axial complex due to traumatic and pathological conditions requires surgical techniques like anterior or posterior screw fixation, interspinous wiring and interlaminar clamping. It can also be useful to devise a new method of fixation of the fractured odontoid process or axis pedicle. The observations of this will provide wide knowledge about the dimensions of the pedicle, the superior articular facet, dens, body and vertebral canal.