Figure 1.

PRISMA flow diagram of the systematic search and selection process. The total number of included studies differs from the number of test treatment or control comparisons because of trials with multiple sham controls or single sham controls used as comparators for multiple active arms. In total, 198 unique sham interventions were included, one of which used twice for a comparison with an active arm and reported in 194 publications. A complete search strings per database and a list of all studies excluded at the full-text screening stage are provided in the supplementary digital content 1, available at http://links.lww.com/PAIN/B671. RCT, randomised controlled trial.