Using transcranial direct current stimulation to improve outcomes and reduce hip osteoarthritis burden (the STIM HIPS study): A protocol for a randomised, triple blind controlled trialKey points

Background: Transcranial direct current stimulation (tDCS), via an electrical current being sent through the brains motor cortex, can elicit pain reduction and improved function in people with knee osteoarthritis (OA), compared to a sham. However, it is unknown whether tDCS-induced reductions in pain can be expected in hip OA given differences between hip and knee OA phenotypes. Methods: Two-armed (n ​= ​39 per arm), triple-blind, randomised controlled trial, with an 8-week intervention window and 8-week post-intervention follow-up assessing the efficacy of real anodal tDCS plus exercise versus sham tDCS plus exercise. Primary outcome measure is the International Hip Outcome Tool–33 (iHOT-33). Aims: The primary objective of this randomised controlled trial is to quantify the effect of tDCS and exercise on pain, disability and quality of life in people with hip OA. Our secondary objectives include: 1) quantifying the influence of motor cortex excitability and conditioned pain modulation on treatment effects, and 2) quantifying the economic cost/benefit of tDCS for improving health-related quality of life in people with hip OA. Analysis: Data distributions will be examined for each outcome and guide preliminary statistical between group test selections. Repeated mixed effects models will determine between-group differences for the primary outcome (iHOT-33), accounting for relevant confounders (i.e., age; sex; body mass index; radiographic severity) with relevant model assumptions examined. Secondary analysis will determine between-group differences for the other outcomes of interest (cortex excitability and conditioned pain modulation). Implications: This randomised controlled trial investigates a novel intervention to improve pain, function and quality of life in people with hip OA.