Moderators and mediators of pain and function outcomes in a new service delivery model for management of knee osteoarthritis in primary care (PARTNER): Secondary exploratory analysis of a randomized controlled trial.

Objective: Explore moderators and mediators influenced changes in pain and function in people with knee osteoarthritis (OA) receiving a new model of primary care service delivery (PARTNER), at 12 months (ACTRN12617001595303).

Methods: Secondary analyses of a cluster randomized controlled trial comparing PARTNER to usual general practitioner-delivered care (n=217, 112 PARTNER, 105 usual care) on knee pain/function. Pain was measured using a Numerical Rating Scale (range 0-10, higher= worse) and the function measured using the function subscale of the Knee Injury and Osteoarthritis Outcome Score (range 0-100, higher= better). Baseline variables selected as potential moderators included age, sex, body mass index, pain duration, residential state, living arrangements, education, employment status, back pain and other joint issues. Mediation variables included physical activity, fear of movement, pain catastrophizing, OA self-management, self-efficacy, sleep, fatigue, quality-of-life, depression, and satisfaction.

Results: For change in pain, no moderators influenced the intervention effect. However, age moderated change in function, with intervention participants <50 years demonstrating greater functional improvement than older counterparts, compared to the control group (50-69 years: coefficient -32.88 [95% confidence interval (95% CI): -45.02, -20.74], >=70 years: coefficient -24.28 [95%CI: -36.53, -12.02]). Mediation analysis revealed significant indirect effects of overall, treatment-related, and symptom-related satisfaction on mean change in pain (-0.10, -0.06, and -0.08, respectively) and function (0.09, 0.05, and 0.07, respectively).

Conclusion: Younger PARTNER participants showed greater functional improvement compared to older age groups (moderating effect). Additionally, indirect mediation effects suggest increased satisfaction across the three satisfaction domains led to reduced knee pain and enhanced function.