Addition of transcranial direct current stimulation to quadriceps strengthening exercise in knee osteoarthritis: A pilot randomised controlled trial

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.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1. Consort diagram for flow of participants through the trial.

Fig 2. Percentage of participants reporting perceived improvement across categories from ‘not changed’ to ‘much improved’.

Note: no participants reported that their condition worsened after either intervention.

Fig 3. Pain and WOMAC physical function subscale (mean and 95% confidence interval) pre- and post-interventions.

Active tDCS + exercise produced improvements in pain and function but sham tDCS + exercise only produced improvement in pain.

Fig 4. Group change in pain (left panel) and WOMAC physical function subscale (right panel).

The graph showed within-group changes (mean and 95% confidence interval) in pain and function following 8 weeks of either active tDCS + exercise or sham tDCS + exercise. Note: larger negative scores indicate greater improvements in pain and function. The dotted line indicates the minimal clinically important change for each outcome.

Fig 5. Pressure pain thresholds (mean and 95% confidence interval) pre- and post-interventions at three knee sites.

Active tDCS + exercise produced greater improvements in pressure pain thresholds at all three sites following 8 weeks of treatment compared with sham tDCS + exercise (A = superolateral knee; B = superior knee; C = superomedial knee).