Study of the Psychometric Properties and a Measure of Utility Determinants ( the SF- 6D) in Patients With Early Inflammatory Low Back Pain

The general main objective of our study is to investigate the psychometric properties, the levels and determinants of the extent of SF- 6D utility in patients followed for recent back pain inflammatory disease. The specific objectives are : * Study the feasibility of the tool considering missing data, distribution, construct validity, reproducibility, sensitivity to change or clinically different groups (discriminative ability) the extent of SF -6D utility . * Study the impact of socio-demographic characteristics, disease characteristics and quality of life, comorbidities at baseline on the measurement of utility and sensitivity to change.

Inclusion Criteria: * The patient should be given free and informed consent and signed the consent * The patient must be affiliated or beneficiary of a health insurance plan * patients aged 18 years and under 50 * inflammatory back pain (buttocks , lumbar or thoracic spine ) * fulfilling the criteria of Calin or Berlin (30,31) * duration of symptoms than three months and less than three years * symptoms suggestive of spondyloarthritis as assessed by the local investigator ( score≥5 on a numerical scale from 0 to 10 where 0 = no evocative and 10 = very suggestive of spondyloarthritis ) . Exclusion Criteria: * Another clearly defined spinal disease (eg discarthrose ) * history of treatment with biotherapy * taking glucocorticoids allowed only in low dose of less than 10mg of prednisone daily and stable for at least four weeks before inclusion * Current or history anomalies that could interfere with the validity of informed consent and / or prevent a patient's optimal adhesion to the cohort (eg , alcoholism , mental illness) .