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[Feasible study for evaluating upper cervical reduction by the clivo-axial angle].

OBJECTIVE
To measure the clivo-axial angle (CAA) and cervicomedullary angle (CMA) in upper cervical deformity patients who underwent computer-assisted posterior upper cervical reduction and fixation surgery, and analyze their correlation.


METHODS
In the study, 25 patients with symptomatic upper cervical deformity were chosen for measurement of preoperative and postoperative CMA and CAA using magnetic resonance imaging (MRI) and intraoperative C-arm. The angle between the clivus plane and the straight line parallel to that of the posterior margin of the C2 vertebral body was defined as CAA; moreover, the angle between the straight line parallel to the ventral side of the cervical spinal cord and the straight line parallel to that of the ventral side of the medulla oblongata was defined as CMA. Two experienced spinal surgeons performed the measurements. The CAA and CMA were measured three times, and the mean value was considered as the result.


RESULTS
Analyses of the CAA and CMA were performed with Wilcoxon rank test, which showed that there was consistency between the CAAs measured with MRI and intraoperative C-arm. The result showed that the postoperative CAA and CMA increased significantly compared with preoperation (P<0.001). Through Spearman rank correlation analysis, the preoperative CAA was positively correlative with the CMA (r=0.902, P<0.001), and so was the postoperative CAA (r=0.921, P<0.001).


CONCLUSION
Preoperative and postoperative CAA in upper cervical deformity patients is significantly correlative with preoperative and postoperative CMA. CAA can be measured during surgery using intraoperative CT or C-arm based three-dimension navigation, and may predict the patient's CMA, which cannot be measured during operation, but is essential for evaluating the decompression and reduction of the spinal cord.