Surgical importance of atlas and axis anatomy

The atlas (first cervical vertebra) and the axis (second cervical vertebra) injuries are the most feared of all vertebral injuries because of their relation to the lower medulla and adjacent spinal cord. Fractures of the atlas account for approximately 1-2% of all fractures and for 2-3% of all acute cervical spine fractures. Atlantoaxial instability results from either a purely ligamentous injury or avulsion fractures. Various techniques has been described for atlantoaxial stabilization. The aim of present study was to determine the anatomical variations of atlas and axis, and to get morphometrical analysis for screw fixation to reduce the complications. The study was performed on 58 atlas vertebrae and 64 axis vertebrae. The measurements obtained from atlas and axis were discussed. The variations of atlas were invastigated as spina bifida in 1.7%, accessory foramen on right side in 8.6%, accessory foramen on left side in 1.7%, canal for vertebral artery in 1.7%, bipartiate superior articular facet in 5.1%. Variants of axis were limited only spina bifida in 1.7 % and corona dentalis in 1.5 %. Some of these anatomical variants may be a cause of certain clinical symptoms which have previously described in the literature. According to the results of the present study, measurements on the vertebrae are different for every individual. The variations of atlas and axis also may have significance for surgery. For this reason, imaging methods and examinations before surgery should be used to describe the anatomy of the region. Keywords: Atlas; axis; screw; fixation; anatomical variations