Morphometric and radiological study of the foramen transversorium of the axis vertebra

ABSTRACT

In this work 250 dried axis vertebrae and CT scan for 50 patients were used to study the foramen transversorium on both sides regarding the presence of erosion, the dimensions of the foramen and its openings, the shape of the openings, the dimensions of the pedicle, the costotransverse bar and the external height of the lateral mass.The anatomical results showed that 6% of the foramina on the left side were markedly eroded [opened] due to the absence of the costo-transverse bar while no erosion was found on the right side. The foramen with its two openings were larger on the left side than on the right side. The right foramen transversorium had a mean height of 0.57 +/- 0.14cm and a mean width of 0.55 +/- 0.11cm while the left foramen had a mean height of 0.61 +/- 0.17cm and a mean width of 0.60 +/- 0.12cm. The diameter of the superior opening of the foramen was wider on the left side [mean = 0.58 +/- 0.I4 cm] than on the right side [mean = 0.54 +/- 0.14cm]. Also, the diameter of the inferior opening had a mean of 0.60 +/- 0.12cm on the left side and 0.55 +/- 0.IIcm on the right side. The superior opening was oval in the majority of the cases [96.80% on the right side and 97.45% on the left side] while-the inferior opening was mostly circular [91.60% on the right side and 92.34% on the left side]. The height of the pedicle had a mean of 0.83 +/- 0.09cm on the right side and 0.78 +/- 0.09cm on the left side while the width of the pedicle had a mean of 0.82 +/- 13cm on the right side and 0.77 +/- 0.17cm on the left side. The costotransverse bar had a mean width of 0.51 +/- 0.l5cm and 0.36 +/- 0.14 on the right and left sides respectively. The lateral mass had a mean height of 0.87 +/- 0.11 and 0.82 +/- 0.14cm on the right and left sides respectively. All these findings may be attributed to the tortuosity of the larger left vertebral artery than the right one. The radiological results were more or less similar to the anatomical results.These results should be taken into consideration in transarticular screw fixation at C1- C2 segment as there is no enough bone to allow adequate fixation. So, CT and vertebral artery angiography should be recommended before any instrumental fixation to avoid injury of the vertebral artery and to ensure a more accurate surgical accurate surgical approach: