Fig. 4

a Sagittal CT image and b sagittal MRI before the first posterior operation, suggesting that the patient had BI and AAD. The spinal cord was compressed from the ventral aspect. c, d Indicating that after posterior distraction and fixation, AAD reduction was not satisfactory, the occipital foramen is enlarged and bone graft fusion is solid. e, f Three months after the operation, CT images suggesting that the odontoid process was fully resected, part of C2 vertebral body was simultaneously resected, and the foramen magnum was further enlarged. g Sagittal MRI revealing decompression of the spinal cord