Measurements of C1-2 region of Cervical Spine Using MRI for C1-2 Transarticular Screw Fixation

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Study design: The C1-2 region was measured using MRI for a C1-2 transarticular screw fixation. Objectives: To measure the first and second cervical spine, using MRI for a C1-2 transarticular screw fixation, and find the safe trajectory for the screw. Summary of Literature Review: Posterior atlantoaxial transarticular screw fixation is an excellent procedure that is associated with high fusion rates. However, there is a potential risk of vertebral artery injury. Materials and Methods : Sagittal MR images, of the cervical spine transecting mid portion of the C1-2 facet joints, were obtained in 24 patients. The mean age of the patients was 45.5 years. The male to female ratio of the patients was 15:9. From the sagittal images the ideal screw trajectory was made, and 48 oblique axial MR images, depending on the ideal screw trajectory in the sagittal plane, were obtained. On the oblique sagittal images, the width of the isthmic portion of the C2, the ideal length of the transarticular screw, the ideal insertion angle of the screw and the ideal entry point were measured using a PACS digital measuring instrument. The location of the vertebral artery was also evaluated. Results: The mean width of the isthmic portion of the C2 was 6.2 mm, ranging from 2.3 to 7.6 mm. The mean ideal screw length was 40.5 mm, ranging from 34.0 to 46.8 mm. The mean ideal insertion angle was 1.1°, ranging from -2.4 to 4.7°, medially. There were no significant differences in the width or the angle in relation to the sex of the patients. However, the length of the screw was significantly longer in the male (42.1 mm) than the female patients (38.0 mm). Three of 24 patients (3 of 48 C1-2 facet joints) had a narrow isthmus due to a high riding vertebral artery. Conclusions: A C1-2 transarticular screw fixation has a risk of injury to the vertebral artery. Therefore, the preoperative measurement of the C1-2 region and an evaluation of the vertebral artery are recommended in each patient. A magnetic resonance image is a useful method for easily evaluating the anatomic structure of the C1-2 region, with no additional study.