The effect of C1 bursting fracture on comparative anatomical relationship between the internal carotid artery and the atlas.

Purpose: To describe the effect of the C1 bursting fracture on the location of the internal carotid artery (ICA) around the atlas.

Methods: The authors analyzed the morphology of the atlas and the ICA in 15 patients with C1 bursting fracture and compared with control group (77 patients) without any pathology. All patients were evaluated with CT angiography for the anatomical assessment. The laterality of the ICA, the distances of the ICA from the midline, anterior tubercle, and ventral surface of the C1 lateral mass were compared between two groups. The distance between the lateral margin of the longus capitis muscle and the inner edge of the transverse foramen was also measured.

Results: Medially located ICA was more common in the C1 bursting fracture group than control group (76.7 vs 42.8 %). There were no significant differences between 2 groups for the distance from the midline, anterior tubercle, and ventral surface of the C1 lateral mass, respectively. The distance of the longus capitis muscle to transverse foramen was 2.52 ± 2.09 and 4.15 ± 3.09 mm in each group, and there was statistically significant difference (p < 0.01).

Conclusions: Lateral displacement of the bony structure of C1 bursting fracture changes the relative location of the ICA medially, which increase the injury risk during the bicortical C1 screw insertion. These data suggest that CT angiography or enhanced CT scans can give critical information to choose the ideal fixation technique and the proper trajectory of the screws for C1 bursting fracture.