Ankylosing spondylitis – Wikipedia

Ankylosing spondylitis is a member of the more broadly defined disease axial spondyloarthritis. Axial spondyloarthritis can be divided into (1) radiographic axial spondyloarthritis (which is a synonym for ankylosing spondylitis) and (2) non-radiographic axial spondyloarthritis (which include less severe forms and early stages of ankylosing spondylitis)

https://en.wikipedia.org/wiki/Ankylosing_spondylitis