Clinic significance of anatomy classifications of vertebral artery-atlas complex

Objective To evaluate the clinical significance of classifying vertebral artery-atlas complex using angiographic CT (computed tomography angiography,CTA).Methods The CTA data of 225 patients were reconstructed three-dimensionally in Mimics.The region of V3 segment of vertebral artery and isthmus of atlas's posterior arch were reconstructed as vertebral artery-atlas complex,classify according to the relationship of the two.The complex types were classed into 3 types and 7 subtypes.Type A was conventional type,which means V3 segment locates above the isthmus of atlas.The distance between vertebral artery and atlas was larger than 1.8 mm in A1 subtype.The distance was between 1.8 and 0.6 mm in A2,and less than 0.6 mm in A3.Type B was variation of vertebral artery.Subtype B1 was far-away variation,which means artery doesn't pass around posterior arch of atlas.Subtype B2 means the artery passed underneath the arch of atlas.Type C was variation of bone.Bone structure was closed in subtype C 1,and unclosed in subtype C2.The distance between artery and atlas was measured in subtype A1 and A2.Results There were 450 cases of vertebral artery-atlas complex in the 225 patients,which could be divided into A1,including 57 (12.7％),A2,including 115 (25.6％),A3,including 194 (43.1％); B1 including 20 (4.4％),B2,including 9 (2.0％); C1,including 34 (7.6％),C2,including 21 (4.7％).More than half patients (50.2％) had different subtype in both sides.The measured value of VAD was 2.42±0.52 and 1.20±0.36 mm in subtype A 1 and A2 respectively.Conclusion Reconstructing CTA images before fixation of atlas can clearly demonstrate the complex of V3 segment of vertebral artery and isthmus of the posterior arch of atlas.Classifying the complex and choose appropriate method of inserting screws can improve the security of the operation. Key words: Atlas;  Vertebral artery;  Anatomy, regional;  Bone screws;  Fracture fixation, internal