Matching the outcomes to treatment targets of exercise for low back pain: does it make a difference? Results of secondary analyses from individual patient data of randomised controlled trials and pooling of results across trials in comparative meta-analyses

Complex interventions, like exercise for non-specific low back pain (NSLBP), have many treatment targets. In randomised controlled trials (RCTs), matching the primary outcome to the exercise target(s) may provide greater standardised mean differences (SMDs) than using unmatched primary outcomes. Objective These secondary analyses of previous RCTs aimed to explore whether using a single matched or composite outcome might impact the results of previous RCTs testing exercise for NSLBP. The first objective was to explore whether a single matched outcome generated a greater SMD when compared to the original unmatched primary outcome SMD. The second objective was to explore whether a composite measure, comprised of matched outcomes, generated a greater SMD when compared to combining the original primary outcome SMD. Design, Setting and Participants We conducted exploratory secondary analyses of data from 1) five RCTs (n=1,033) that used an unmatched primary outcome but included (some) matched outcomes as secondary outcomes, and 2) four RCTs (n=864) that included multiple matched outcomes by developing composite outcomes. Intervention: Exercise compared to no exercise. Main Outcome Measures: The composite consisted of standardised averaged matched outcomes. All analyses replicated the RCTs’ primary outcome analyses. Results Of five RCTs, three had greater SMDs with matched outcomes (pooled effect SMD 0.30 (95% CI 0.04, 0.56), p=0.02) compared to an unmatched primary outcome (pooled effect SMD 0.19 (95% CI -0.03, 0.40) p=0.09). Of four composite utcomeanalyses, three RCTs had greater SMDs in the composite outcome (pooled effect SMD 0.28 (95%CI 0.05, 0.51) p=0.02) compared to the primary outcome (pooled effect SMD 0.24 (95%CI -0.04, 0.53) p=0.10). Conclusion These exploratory analyses suggest that using an outcome matched to exercise treatment targets in NSLBP RCTs may produce greater SMDs than an unmatched primary outcome. Composite outcomes could offer a meaningful way of investigating superiority of exercise than single domain outcomes.