Conventional radiography is a well-established method for detecting structural spinal changes such as new bone formation between the vertebral bodies and vertebral fusions. In manifest disease radiography often gives a good overview of structural changes.

For the diagnosis of spinal changes lateral as well as frontal radiographs are needed. However, despite using two planes the thoracic spine can be difficult to evaluate on radiographs due to overlaying structures such as lung tissue. Supplementary MRI may be needed in early stages and for monitoring the disease during therapy. MRI can display signs of activity which cannot be obtained by radiography.

If fracture is suspected, but cannot be diagnosed or excluded by radiography supplementary CT may be necessary and also MRI in the case of spinal cord or nerve lesion.

The radiographic AS changes vary with the disease duration and severity as illustrated below.