Conventional radiography is a well established method for detecting structural spinal changes such as new bone formation between the vertebral bodies and fusions.
There are several methods for assessing the severity of abnormalities in ankylosing spondylitis and the method used often depends on local tradition. The internationally recommended method by rheumatologists is the modified SASS method. It is simple to use, but from a radiologist’s point of view all relevant image information is not taken into account. This is more the case when using the BASRI method.
Knowledge about the normal composition of the spine is necessary for understanding the description of the different grading methods.