Dosage of pain rehabilitation programmes for patients with chronic musculoskeletal pain: a non-inferiority randomised controlled trial.

To analyse the effects of interdisciplinary pain rehabilitation programmes with different dosages; care as usual versus short form. A single blinded, two armed, randomised controlled trial, with non-inferiority design was performed. All patients with chronic musculoskeletal pain referred to an outpatient multidisciplinary pain rehabilitation programme were eligible for this study. Only dosage differed, content was similar. The difference on Pain Disability Index was the primary outcome measure. Four points difference on Pain Disability Index was applied as a non-inferiority margin. Treatment effects within groups were expressed in standardised mean difference and effect sizes were calculated between the groups. Because care as usual was frequently extended, the difference in dosage between groups was limited. The study was stopped prematurely because of an a-priori stopping rule. Interim analyses are presented. Both groups (care as usual  = 58, short form  = 54) improved significantly (mean Pain Disability Index change care as usual: -10.8; short form: -8.3). Mean difference between groups was 2.5 points (95% confidence interval was -2.2 to 7.3). Effect size between groups was 0.2. The 95% confidence interval for the difference in mean pain disability reduction exceeded the upper limit of the non-inferiority margin. The results of the primary analyses of this trial are, therefore, inconclusive. Ancillary analyses revealed that programme dosage was not associated with differences in the disability outcomes. Implications for rehabilitationOptimum dosage of interdisciplinary pain rehabilitation programs is unknown and scarcely studied. This study is the first to analyse dosage as primary aim.Although results are inconclusive, they also suggest that differences in dosage may not automatically lead to differences in effects.Further research is needed to analyse what dosage works for whom; to detect optimum effective and cost-effective dosage of pain rehabilitation programmes.