Trends over time in the size and quality of randomised controlled trials of interventions for chronic low-back pain

Previous reviews of randomised controlled trials (RCTs) for low-back pain (LBP) have failed to identify any positive trend in study quality with more recent years of publication. This study aimed to identify and describe trends over time in the study design characteristics and risk of bias in chronic LBP trials performed over the past 30 years. One fifty-seven randomised trials of interventions for chronic LBP were extracted from recently published systematic reviews. The reviews included RCTs on physical and rehabilitation interventions, injection therapy and denervation procedures, complementary and alternative therapies and pharmacological interventions for chronic LBP. Study level data were extracted and analysed for trends associated with year of publication. Overall, the mean sample size in the RCTs was 141 (median 70; range 17-3093). There was a slight increase in the median number of risk of bias criteria fulfilled from trials published prior to 1995 to those published after 1996. The analysis showed that in more recent years RCTs of medical interventions were more likely to be successfully blinded than RCTs of non-medical interventions. The continuing uncertainty regarding the efficacy of many interventions for chronic LBP again stresses the need for large RCTs with low risk of bias. Further research is needed into specific risks of bias within the RCTs for chronic LBP and the effect they have on the plausibility of the results.