Conventional radiography has for many years been used to diagnose sacroiliitis and the findings by radiography are still part of the accepted international diagnostic criteria for ankylosing spondylitis. However, radiography can only show permanent (structural) damage of the joints and/or bone. The diagnosis can therefore be difficult to obtain and may be delayed for many years unless radiography early in the disease is replaced or supplemented by cross sectional imaging (CT or MRI).
In later stages of the disease detection of both sacroiliitis and spinal changes can often be obtained by radiography.
The technology behind radiography is relatively simple and there are internationally accepted grading system for both sacroiliac joint and spinal abnormalities.