NSAIDs Added to Anti-TNF Therapy Versus Anti-TNF Therapy Alone on Progression of Structural Damage in Ankylosing Spondylitis

Major Inclusion Criteria: * Definite diagnosis of AS according to the "modified New York criteria". * History of an inadequate response to ≥2 NSAIDs taken for at least 2 weeks each. * Active disease as defined by a Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) value of ≥4 at screening. * Presence of at least one of the following risk factors for radiographic spinal progression: 1. Elevated C reactive protein (CRP; \>5mg/l) at screening at the absence of reasons for elevated CRP other than AS; 2. Presence of ≥ 1 syndesmophyte on prior X-rays of the spine. * Subject is a candidate for anti-TNF therapy based on the Investigator's opinion. * Subject is able and willing to give a written informed consent and comply with the requirements of the study protocol. Only patients who give written informed consent will be included in the trial. * If female: either unable to bear children (postmenopausal for at least 1 year or surgically sterile) or is willing and able to practice a reliable method of contraception throughout the study and 6 months after Inclusion Criterion for Phase II (randomized part of the study): \- adequate response to Golimumab during Phase I (referred to as decline in BASDAI) Major Exclusion Criteria: * For female subjects: pregnancy or lactating * subjects with chronic inflammatory articular disease other than spondyloarthritis / AS or systemic autoimmune disease, e.g. systemic lupus erythematosus, Sjögren´s syndrome, rheumatoid arthritis. * history of inadequate response to anti-TNF-therapy * intolerability/hypersensitivity to one of the drugs or other components of the study medication * presence ot total spinal ankylosis * contraindications to anti-TNF-therapy (current or remitting clinical significant infections, tuberculosis, viral hepatitis, HIV; malignancies; demyelinating disease; vaccination with live vaccine within 3 months before, during and until 6 months after study) * (relative) contraindications to Celecoxib therapy (uncontrolled arterial hypertension, high cardiovascular risk / history of cardiovascular events; history of gastrointestinal ulcers or relevant bleeding; known M. Crohn or ulcerative colitis) * diagnosis of fibromyalgia * significant lab abnormalities