The Relationship Between Cervical Sagittal Balance and Type of Atlantoaxial Dislocation Secondary to Os Odontoideum.

OBJECTIVE

To analyze the effect of cervical sagittal balance on the direction and type of atlantoaxial dislocation.

METHODS

Data of 55 patients seen at our hospital for atlantoaxial instability/dislocation caused by os odontoideum were reviewed. Radiographic variables, including T1 slope (T1S), C1-C2 angle, C2-C7 angle, C1-C2 sagittal vertical axis (SVA), C2-C7 SVA, and atlanto-dens interval (ADI), were measured preoperatively. Patients were divided into three groups according to ADI: anterior atlantoaxial dislocation, atlantoaxial instability, and posterior atlantoaxial dislocation. Differences within and between groups in radiographic variables and relationships between the investigated variables were analyzed.

RESULTS

ADI was strongly negatively associated with C1-C2 angle (r = -0.805, P < 0.05); whereas ADI had a medium-strength positive relationship with C2-C7 angle (r = 0.425, P < 0.05) and a medium-strength negative relationship with C2-C7 SVA (r = -0.411, P < 0.05). However, ADI was not significantly correlated with T1 slope (r = -0.092, P > 0.05).

CONCLUSIONS

The type and direction of atlantoaxial dislocation is closely associated with cervical sagittal balance. C2-C7 SVA is an important factor in assessing the direction of atlantoaxial subluxation secondary to os odontoideum. ADI decreases with increasing C2-C7 SVA. The larger the C2-C7 SVA, the more likely the atlantoaxial dislocation is to be posterior.