Abstract
A randomised, assessor- and participant-blind, sham-controlled trial was conducted to assess the safety and feasibility of adding transcranial direct current stimulation (tDCS) to quadriceps strengthening exercise in knee osteoarthritis (OA), and provide data to inform a fully powered trial. Participants were randomised to receive active tDCS+exercise (AT+EX) or sham tDCS+exercise (ST+EX) twice weekly for 8 weeks whilst completing home exercises twice per week. Feasibility, safety, patient-perceived response, pain, function, pressure pain thresholds (PPTs) and conditioned pain modulation (CPM) were assessed before and after treatment. Fifty-seven people were screened for eligibility. Thirty (52%) entered randomisation and 25 (84%) completed the trial. One episode of headache in the AT+EX group was reported. Pain reduced in both groups following treatment (AT+EX: p<0.001, partial η2 = 0.55; ST+EX: p = 0.026, partial η2 = 0.18) but no between-group differences were observed (p = 0.18, partial η2 = 0.08). Function improved in the AT+EX (p = 0.01, partial η2 = 0.22), but not the ST+EX (p = 0.16, partial η2 = 0.08) group, between-group differences did not reach significance (p = 0.28, partial η2 = 0.052). AT+EX produced greater improvements in PPTs than ST+EX (p<0.05) (superolateral knee: partial η2 = 0.17; superior knee: partial η2 = 0.3; superomedial knee: partial η2 = 0.26). CPM only improved in the AT+EX group but no between-group difference was observed (p = 0.054, partial η2 = 0.158). This study provides the first feasibility and safety data for the addition of tDCS to quadriceps strengthening exercise in knee OA. Our data suggest AT+EX may improve pain, function and pain mechanisms beyond that of ST+EX, and provides support for progression to a fully powered randomised controlled trial.
Highlights
Knee osteoarthritis (OA) is a prevalent and costly health problem with no known cure
conditioned pain modulation (CPM) was examined as a change in pain perceived in one body region as a result of pain induced in another body region
In the active tDCS+exercise (AT+EX) group, one participant withdrew after having an unrelated fall at home and the second relocated to another city
Summary
Knee osteoarthritis (OA) is a prevalent and costly health problem with no known cure. Evidence from healthy individuals and groups with chronic pain suggests anodal tDCS applied to the primary motor cortex (M1) can reduce pain through modulation of pain processing in cortical and subcortical regions, facilitation of descending anti-nociceptive pathways, and induction of synaptic change, reminiscent of neuroplasticity, in underlying brain regions [16,17,18,19] On this basis, applying anodal tDCS to M1 in addition to the established exercise therapy for knee OA has the potential to bolster the mechanistic and clinical effects of exercise through two mechanisms: i) ‘priming’ the brain to increase its responsiveness to the corticomotor benefits of exercise (e.g. increased cortical excitability, enhanced voluntary muscle activation, strength gains, improved muscle coordination and motor control) and/or; ii) additive and complementary effects on pain system function which has been argued as an outcome of exercise [20]. This pilot randomised clinical trial aimed to: i) determine the safety, feasibility and patientperceived response of adding tDCS to an exercise program for knee OA; and ii) provide data to inform a sample size calculation for a fully-powered trial based on trends of efficacy in pain, physical function and pain system function should these be observed
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