Can non-invasive brain stimulation enhance the effect of exercise on knee osteoarthritis (OA) pain?

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Osteoarthritis (OA) is the most common cause of chronic pain and disability in older adults and is associated with muscle weakness, functional limitations, psychological distress, fear of movement and reduced quality of life. Knee OA accounts for the majority of the burden of OA worldwide. Exercise can effectively reduce pain in knee OA and is universally recommended as a first-line treatment by international evidence based treatment guidelines. Exercise also produces immediate, short term reductions in pain sensitivity after a single bout of exercise, called exercise induced hypoalgesia (EIH). However, higher levels of EIH variability can be seen in chronic pain conditions such as knee OA, with some people experiencing no change or even an increase in pain after exercise. Recent evidence in a healthy pain-free population has shown that a non-invasive brain stimulation technique called transcranial direct current stimulation (tDCS), can enhance EIH. The effects of such an intervention have not yet been examined in an OA population, where EIH is known to be more variable. We will therefore conduct a double blind randomised controlled cross-over trial examining the effect of active tDCS on EIH compared to sham tDCS in people with OA. Each participant will attend two clinical visits (1-2 hours) at Auckland University of Technology a minimum of 7 days apart. The order of sessions (active/sham tDCS) will be randomised for each participant. In the active tDCS session, participants will receive 20 min of 2 mA anodal stimulation. In the sham tDCS session, participants will receive 20 min of sham tDCS. After this, EIH will be measured in response to a standardised bout of resistance exercise. All assessments will be performed by a blinded assessor. The study will test whether a single session of 2mA active tDCS over the primary motor cortex enhance EIH compared to sham tDCS in individuals with knee OA.