Identifying potential moderators of first-line treatment effect in patients with musculoskeletal shoulder pain: a systematic review

Background: Commonly used conservative shoulder pain treatments include: advice/analgesia, exercise/manual therapy and, corticosteroid injection. Moderators, patient/clinical attributes influencing treatment effect, facilitate clinical decision-making by identifying which patients might respond best to specific treatments. This review summarises results of studies aiming to identify/test treatment effect moderators. Methods: Randomised controlled trials (RCTs) containing some form of, or suggested moderation/subgroup analysis (sample size >20, and >10 subjects in smallest subgroup), comparing above treatments against physical/functional/pain outcomes, in adults with shoulder pain were searched for in Medline, Embase, PsychInfo, CINAHL, AMED, Pedro, Cochrane Database. Cochrane Risk of Bias tool and Pincus criteria for moderation analysis were applied. Results: Six RCTs aiming to identify/test moderators and 16 suggesting potential moderators were included and data narratively synthesised. One trial offered confirmatory level moderation (Pincus criteria). Graded exercise had smaller effect in those with painful arc at baseline, compared against without, although lacked statistical significance (mean difference -14.0 shoulder disability (0-100 scale), 95% CI's [-28.1, 0.1], p = 0.05). Twenty other factors with insufficient level moderation evidence were identified. Discussion: Review highlights lack of high-quality evidence for moderators of treatment effect of shoulder pain treatments. Future research should address proposed candidate moderators, using robust moderation methodologies to inform clinical decision-making.