Clinical criteria

1) Low back pain persisting for ≥3 months, reduced by exercise and not relieved by rest

2) Limited motion in the lumbar spine in coronal and sagittal planes

3) Limited chest expansion compared with normal values for age and sex

Radiologic criterion

Grade 3-4 unilateral or grade 2-4 bilateral sacroiliitis

Definite ankylosing spondylitis: The radiologic criterion and ≥1 of clinical criteria are fulfilled.

Probable ankylosing spondylitis: Three clinical criteria are fulfilled or the radiologic criterion alone is fulfilled.