[Analysis of veracity of the C1 lateral mass screw insertion in the atlantoaxial fixation].

OBJECTIVE: To evaluate the veracity of the C1 lateral mass screw insertion in the atlantoaxial fixation using plate and screw method without A-P fluoroscopic guiding. METHODS: In the atlantoaxial fixation, without A-P fluoroscopic guiding, we probe lateral mass edge and identify the entrance point of C1 lateral mass screw indirectly. 159 patients treated with atlantoaxial fixation using plate and screw method were studied. Postoperative CT was used for analysis, and the position of the lateral mass screws in atlas was identified by coronary and axial CT scan. Three areas were delimited in and around the lateral mass of atlas in the axial CT scan, so as to analyze the location of screws: area A (inside the joint face), area B (outside the joint face but still in lateral mass), and area C (outside the lateral mass). RESULTS: Among the 318 screws, 308 (96.9%) were located in area A, 5 in area B (1.6%), and 5 in area C (1.6%). All cases got atlantoaxial union at 4 months after operation. CONCLUSION: Probing lateral mass edge and identifying the lateral mass indirectly is reliable for identifying the path of screw in atlas.