Background: Sacroiliitis in ankylosing spondylitis has frequently been graded radiographically using the New York (NY) criteria, which also have been applied in computed tomography (CT).
Purpose: To validate the grading of the NY criteria in CT of the sacroiliac joints.
Material and methods: With the aid of the NY criteria, assessment of inflammatory and degenerative changes was made in 1304 CT studies. Assessment included erosions, the distribution, type, and width of sclerosis, and the involvement of the joints in sacroiliitis, as well as of normal anatomic variants such as joint space width and shape.
Results: There was definite radiological sacroiliitis in 420 joints in 251 patients. Among these, more than two-thirds of the joint was involved in 71.0% of the affected joints. Sclerosis of the ilium was much more prevalent than sacral sclerosis. With increasing NY grade, iliac sclerosis, width, and extent increased, transition from sclerosis to normal bone became indistinct, and the structure of sclerosis was more inhomogeneous. Erosions of the joint surfaces were localized predominantly on the iliac side.
Conclusion: Only erosions seem to be a valid solitary diagnostic sign. Solitary erosions need supplemental evidence from other inflammatory signs. Inflammatory sclerosis may be distinguished from degenerative sclerosis, and can sometimes support early diagnosis. Joint space width, joint shape, bone mineral content, or enthesopathy have no place in sacroiliitis diagnosis on CT. The NY criteria are not ideal for use with CT. A practical classification of sacroiliitis on CT is proposed, with a grading of no disease, suspected disease, and definite disease.