Noninvasive electrical stimulation on pain and function in knee osteoarthritis in middle-aged and older adults: systematic review and meta-analysis of randomized clinical trials

Introduction: Knee osteoarthritis (KOA) is one of the most common musculoskeletal disorders in older adults, often leading to chronic pain, functional decline, and reduced quality of life. Conventional rehabilitation strategies frequently achieve only partial relief, which has stimulated interest in non-invasive electrical stimulation (NIES) as an adjunctive therapy. Therefore, the aim of this study was to synthesize the available evidence on the effects of NIES on pain and function in middle-aged and older adults with knee osteoarthritis. Methods: This systematic review and meta-analysis, conducted in accordance with PRISMA guidelines, evaluated randomized and controlled trials investigating the effects of transcranial direct current stimulation (tDCS), neuromuscular electrical stimulation (NMES and WB-EMS), transcutaneous electrical nerve stimulation (TENS), and innovative modalities such as cranial electrical stimulation (CES) and transcutaneous vagus nerve stimulation (tVNS). Results: A total of 15 randomized controlled trials, including 1,137 participants, met the inclusion criteria. The overall pooled analysis demonstrated significant improvements in pain and function with NIES, though heterogeneity was high. Subgroup analyses showed that tDCS produced consistent, moderate analgesic effects, while NMES and WB-EMS improved quadriceps strength, mobility, and patient-reported outcomes, especially in individuals with muscle weakness. TENS yielded the most variable results, with limited efficacy beyond short-term analgesia. CES and tVNS were supported by only two small trials, suggesting potential benefits but precluding pooled analysis. Conclusion: NIES appears to be a safe and promising adjunct in multimodal rehabilitation for KOA, though further large-scale, high-quality trials are required to confirm its clinical effectiveness. Systematic Review Registration: identifier: CRD420251174723.