Table 1.

Modified New York criteria for ankylosing spondylitis ref.[3]

A. Diagnosis*
1. Clinical criteria
a)		Low back pain and stiffness for more tan three months, which improves by exercise, but is not relieved by rest
b)		Limitation of motion of the lumbar spine in both the sagittal and frontal planes
c)		Limitation of chest expansion relative to normal values correlated for age and sex
2. Radiological criterion:
Sacroiliitis grade ≥2 bilaterally or grade 3–4 unilaterally
B. Grading
1.	Definite ankylosing spondylitis is considered if the radiologic criteria is associated with at least one clinical criterion
2.	Probable ankylosing spondylitis if:
	a)	Three clinical criteria are present
	b)	The radiologic criterion is present without any signs or symptoms satisfying the clinical criteria (other causes of sacroiliitis should be considered)
Radiographic criteria
Grade 0 = normal
Grade 1 = suspicious changes
Grade 2 = minimal abnormality – small localized areas with erosions or sclerosis, without alteration in the joint width
Grade 4 = severe abnormality –total ankylosis.

*The modified New York criteria for ankylosing spondylitis are mostly used for classification.

All three clinical and the radiographic criteria refer exclusively to axial involvement, including the spinal, costovertebral, costosternal, and sacroiliac joints.

The proportion of children and adolescents that fulfill those criteria before they reach the age 17 years is probably <15%. In such a case they usually have a combination of peripheral and axial symptoms.

It is assumed that stated otherwise, publications on ankylosing spondylitis never refer to definite or probable disease, but to definite ankylosing spondylitis.