Fig. 6

Subaxial instability. (a) Flexion view in a 64-year-old woman with advanced peripheral RA showing anterior atlanto-axial instability as well as subaxial instability at multiple levels. (b) Flexion view 2 years later after surgical stabilisation of the atlanto-axial region demonstrates progression of the subaxial instability, especially between C3 and C4 (white arrow). There is a characteristic “stepladder” appearance, which also occurred on the initial radiographs (a), but is less pronounced