Patients entering the study were ≥18 years of age and fulfilled the modified New York (mNY) criteria for AS, confirmed by centralised reading of sacroiliac (SI) radiographs. Patients had active disease based on Bath AS Disease Activity Index (BASDAI) score ≥4 and back pain score ≥4 and history of either inadequate response to ≥2 oral NSAIDs or intolerance to prior NSAIDs. Patients with C reactive protein (CRP) levels within the normal reference range and those with active arthritis, enthesitis or psoriasis could be enrolled, provided mNY criteria for AS were met. Patients were permitted to continue concurrent treatment with methotrexate, sulfasalazine and stable oral corticosteroids (<10 mg/day of prednisone or equivalent). No eligibility criteria relating to MRI were specified. Exclusion criteria (see online supplementary section 1) included current or prior biological DMARD treatment and evidence of active, latent or inadequately treated tuberculosis infection.
Patients were recruited at 58 centres globally (see online supplementary section 2). The study was conducted in accordance with applicable legal and regulatory requirements, and the general principles set forth in the International Ethical Guidelines for Biomedical Research Involving Human Subjects, International Conference on Harmonisation Guidelines for Good Clinical Practice and the Declaration of Helsinki. All patients provided written informed consent. Institutional review boards or independent ethics committees at each investigational centre approved the study.