Intramuscular electrical stimulus potentiates motor cortex modulation effects on pain and descending inhibitory systems in knee osteoarthritis: a randomized, factorial, sham-controlled study.

Background: Neuroplastic changes in nociceptive pathways contribute to severity of symptoms in knee osteoarthritis (KOA). A new look at neuroplastic changes management includes modulation of the primary motor cortex by transcranial direct current stimulation (tDCS). Objectives: We investigated whether tDCS combined with intramuscular electrical stimulation (EIMS) would be more efficacious than a sham (s) intervention (s-tDCS/s-EIMS) or a single active(a)-tDCS/s-EIMS intervention and/or s-tDCS/a-EIMS in the following domains: pain measures (visual analog scale [VAS] score and descending pain modulatory system [DPMS], and outcomes, and analgesic use, disability, and pain pressure threshold (PPT) for secondary outcomes. Registration: The trial is registered in Clinical trials.gov: NCT01747070. Methods: Sixty women with KOA, aged 50-75 years old, randomly received five sessions of one of the four interventions (a-tDCS/a-EIMS, s-tDCS/s-EIMS, a-tDCS/s-EIMS, and s-tDCS/aEIMS). tDCS was applied over the primary motor cortex (M1), for 30 minutes at 2 mA and the EIMS paraspinal of L1-S2. Results: A generalized estimating equation model revealed the main effect of the a-tDCS/aEIMS in the VAS pain scores at end treatment compared with the other three groups (P<0.0001). There existed a significant effect of time and a significant interaction between group and time (P<0.01 for both). The delta-(Delta) pain score on VAS in the a-tDCS/a-EIMS group was -3.59, 95% CI: -4.10 to -2.63. The (Delta) pain scores on VAS in the other three groups were: a-tDCS/sEIMS=-2.13, 95% CI: -2.48 to -1.64; s-tDCS/a-EIMS=-2.25, 95% CI: -2.59 to -1.68; s-tDCS/s-EIMS MR=-1.77, 95% CI:-2.08 to 1.38. The a-tlX;S/a-EIMS led to better effect in DPMS, PPT, analgesic use, and disability related to pain. Conclusion: This study provides additional evidence regarding additive clinical effects to improve pain measures and descending pain inhibitory controls when the neuromodulation of the primary motor cortex with tDCS is combined with a bottom-up modulation with EIMS in KOA. Also, it improved the ability to walk due to reduced pain and reduced analgesic use.