The Effect of Transcranial Direct Current Stimulation on Pain in Knee Osteoarthritis: A Systematic Review and Meta-analysis of Clinical Trials

Background: Knee Osteoarthritis (OA) is a common degenerative joint disease characterized by ongoing pain and reduced physical function.Objectives: We aimed to systematically review and meta-analyze the clinical trials that evaluated the impact of transcranial Direct Current Stimulation (tDCS) on knee OA pain.Methods: A comprehensive search was performed on Scopus, Web of Science, PubMed/MEDLINE, EMBASE, ProQuest, CENTRAL via Cochrane, and PEDro from the inception of these databases until May ۳۱, ۲۰۲۳ with no language restrictions. The objective of the search was to find publications that examined the impact of active tDCS compared to sham tDCS or other interventions in individuals with knee OA.Results: The meta-analysis comprised ten studies including ۵۱۷ patients with knee OA. Active tDCS resulted in significantly lower pain scores compared to sham tDCS/ Transcutaneous Electrical Nerve Stimulation (TENS) immediately (effect sizes from pre-test–post-test-control design (dppc۲) = -۰.۸۳, I۲ = ۶۱.۸%), short-term (dppc۲ = -۰.۷۴, I۲ = ۴۳.۵%), and mid-term (dppc۲ = -۱.۹۴, I۲ = ۸۷.۸%) follow-ups, but not in the long term (dppc۲ = -۰.۲۵, I۲ = ۲۹.۶%). However, the certainty of the evidence was assessed as low to very low.  Moreover, function was significantly improved with active tDCS immediately after the last treatment session either by McMaster Universities Osteoarthritis Index (WOMAC) or Knee Injury and Osteoarthritis Outcome Score (KOOS) (dppc۲ = -۰.۳۸, I۲ = ۶.۶% and dppc۲ = ۰.۸۷, I۲ = ۶۰.۱%, respectively). The certainty of the evidence was very low. No serious adverse effects of tDCS were reported by the majority of studies.Conclusion: More than half of the included trials had unclear or high risk of bias and there were no patient follow-ups beyond three months. Given the criteria of reduced I۲ and sufficient number of studies, no potential sources of heterogeneity were identified. Further high-quality randomized clinical trials with extended follow-up periods are required to determine the true effects of tDCS on knee OA.

Keywords:

Knee osteoarthritis , Meta-analysis , Pain , Systematic review , Transcranial direct current stimulation