Sample size calculation: The principal assessment criterion is DAS variations at 1 year. The expected statistical power is 80% (the type I risk being set at 5%) and the standard deviation common to the two samples for DAS variation is evaluated at 1.5. With these hypotheses, the inclusion of 100 patients in the study group and 100 patients in the control group will produce an effect size of 0.40 (i.e. a difference in DAS between the two groups equal to 0.6).