Fig. 4

MRI and cervical lateral radiography of a patient with rheumatoid arthritis in ADS group. (a) A sagittal T2-weighted fast spin-echo image with iterative decomposition of water and fat using echo asymmetry and least-squares estimation (IDEAL) fat saturation demonstrates high signal intensity at the anterior atlantodental interval (arrows). Additionally, there is disruption of the smooth curvature of the spinolaminar line and edema within the interspinous ligament (dashed arrow). (b) A sagittal T1-weighted fast spin-echo image reveals a widened anterior atlantodental interval (4 mm). (c, d) In lateral cervical radiography with neutral (c) and flexion posture (d), the anterior atlantodental interval is positive with 6.62 mm in neutral posture and 5.87 mm in flexion posture (cut off value: >3 mm). Swischuk line method is also positive with 2.49 mm in neutral posture and 2.04 mm in flexion posture, applying either 1 or 2 mm cut- off values