No Effect of a Single Session of Anodal Transcranial Direct Current Stimulation on Exercise-induced Hypoalgesia in Knee Osteoarthritis: A Randomized Cross-over Trial

Abstract

BACKGROUND: Exercise induces short-term pain relief (exercise-induced hypoalgesia, EIH), but this response is often blunted in people with knee osteoarthritis (OA). Transcranial direct current stimulation (tDCS) has been proposed as a potential enhancer of EIH. OBJECTIVE: This study aimed to determine whether a single session of 2-mA anodal tDCS applied for 20 minutes over the contralateral primary motor cortex augments the exercise-induced hypoalgesic response to isometric quadriceps exercise in individuals with knee OA. MATERIALS AND METHODS: In this double-blind randomized cross-over trial, 27 participants with knee OA completed two experimental sessions (active anodal tDCS + exercise; sham tDCS + exercise) in counterbalanced order. Pressure pain thresholds (PPTs at the knee and forearm), resting knee pain, and evoked knee pain during stepping were assessed pre- and post intervention. Linear mixed models compared pre- and postexercise changes between active and sham conditions. Blinding success was evaluated using Bang's blinding index. RESULTS: Both sessions produced EIH (knee PPT increased pre-to-post; all p ≤ 0.001). Between active and sham conditions, there were no significant differences for knee PPT (mean difference 0 kPa [95% CI -50 to 40], p = 0.82), forearm PPT (-20 kPa [-60 to 30], p = 0.45), resting knee pain (1/100 [-13 to 15], p = 0.89), or evoked knee pain (1/100 [-7 to 8], p = 0.14). Blinding was successful, and no adverse events were reported. CONCLUSIONS: These findings indicate that a single session of anodal tDCS does not augment the immediate EIH response to isometric quadriceps exercise in people with knee OA. PERSPECTIVE: This randomized cross-over trial found that anodal tDCS did not enhance EIH in people with knee OA. These findings suggest that a single session of anodal tDCS does not meaningfully augment the immediate exercise-induced hypoalgesic response in individuals with knee OA. CLINICAL TRIAL REGISTRATION: The Australian New Zealand Clinical Trials Registry number for the study is ACTRN12621000787886, registered July 1, 2021, prospectively.