Sample size: 17 patients per group, plus 2 patients per group because of loss, supposes an improvement in the study group of 60% to 90%, with a confidence level of 95% to 99% (two tails test) and a power of 80% to 90%, with improvement in the control group of only 10%. The basis of such calculations is indirect because there are no data about juvenile SpA; yet, data on adults treated with infliximab and children and teenagers treated with sulfasalazine compared to placebo exist.