POS1106 MEDIATORS OF THE EFFECT OF THERAPEUTIC EXERCISE ON PAIN AND FUNCTION IN PATIENTS WITH KNEE AND HIP OSTEOARTHRITIS; AN INDIVIDUAL PATIENT DATA MEDIATION STUDY FROM THE OA TRIAL BANK.

Abstract

BackgroundCurrently, there is no cure for osteoarthritis (OA). Therapeutic exercise is recommended in all international guidelines to improve pain and function (1). However, randomised controlled trials (RCTs) investigating therapeutic exercise showed that, on average, effect sizes are small to moderate compared to non-exercise controls (2-3). Better knowledge about how therapeutic exercise works to improve pain and function could help improve the design and delivery of future therapeutic exercise interventions and potentially improve patient outcomes.ObjectivesTo evaluate the mediating effects of 1) muscle strength, proprioception, and range of motion (ROM) among patients with knee OA, and 2) muscle strength among patients with hip OA, using the procedures established for Individual Participant Data (IPD) analyses by the OA Trial Bank.MethodsRelevant IPD were sought from all published RCTs comparing therapeutic exercise to a non-exercise control group among people with knee and/or hip OA, using previously published methods (4). For each potential mediator separately, the effect of exercise on the absolute change in pain/function directly after the intervention was determined, controlling for the relative change in mediator under investigation and potential mediator-outcome confounders, using the ‘counterfactual framework’ (5). Next, the effect of exercise on the relative change in the mediator was determined. The percentage mediated was calculated by dividing the natural indirect effect by the total effect.ResultsWe obtained IPD from 12 RCTs and 1407 participants (knee OA = 1113; hip OA n=294) that were eligible for inclusion in one or more mediation analyses. Therapeutic exercise showed a significant effect on the relative change in muscle strength in knee OA, but not for proprioception or ROM in knee OA, nor for muscle strength in hip OA. Of all mediators, only the change in muscle strength had a significant effect on the change in pain in knee OA, and on function in knee OA and in hip OA. The percentage mediated for each mediator and each outcome was small (5.3% or less, see Table 1).Table 1.Percentage mediated for all potential mediators, by outcome and joint.Knee OAPainKnee OAFunctionHip OAPainHip OAFunctionMuscle strength2.4%2.3%absentabsentProprioceptionabsent0.2%--Range of motion1.8%5.3%--‘absent’: no percentage mediated calculated, since direct and indirect effect had opposite directions.‘-‘: factors not considered a potential mediator for therapeutic exercise in hip OA.ConclusionIn the first IPD mediation analysis to our knowledge of this scale, muscle strength, proprioception and ROM did mediate the effect of therapeutic exercise for pain and function in knee OA, but only to a very small degree. We observed no such mediating effect of muscle strength for therapeutic exercise in patients with hip OA. The challenge remains to better understand the key mechanisms of action of therapeutic exercise for knee and hip OA, so that exercise interventions can be designed and delivered to target these and therewith optimise the effects for patients.