Shoulder pain: Is the outcome of manual therapy, acupuncture and electrotherapy different for people with high compared to low pain self-efficacy? An analysis of effect moderation

Background: High baseline pain self-efficacy (PSE) predicts a better outcome for people attending physiotherapy for musculoskeletal shoulder pain. A potential contributing factor is that PSE moderates the relationship between some treatment modalities and outcome. Our aim was to investigate whether there is a difference in outcome between participants with high compared to low PSE receiving manual therapy, acupuncture, and electrotherapy. Methods: Participants were stratified into high or low baseline (i) PSE, (ii) shoulder pain and disability index (SPADI), and (iii) did or did not receive the treatment. Whether the effect of treatment differs for people with high compared to low PSE was assessed using the 95% confidence interval of the difference of difference (DoD) at a 5% significance level (p < 0.05). Results: Six-month SPADI scores were consistently lower (less pain and disability) for those who did not receive passive treatments compared to those who did (statistically significant in 7 of 24 models). However, DoD was statistically insignificant. Conclusion: PSE did not moderate the relationship between treatment and outcome. However, participants who received passive treatment experienced equal or more pain and disability at 6 months compared to those who did not. Results are subject to confounding by indication but do indicate the need for further appropriately designed research. Level of Evidence: Level of evidence II-b.