Fig. (1) (a-c) A patient with rheumatoid arthritis (case 4): after the application of a posterior CCD system, the sagittal profile of the cervical spine and the C1-C2 stability was restored and maintained during an 18 months follow-up. (a) MRI scan: C1-2 instability, vasilar invagination, and cord compression are obvious, (b) 2^nd post-op day, (c) 18^th post-op month.