Neuromuscular Electrical Stimulation for Knee Osteoarthritis: A Meta-analysis of Randomized Controlled Trials Evaluating Pain, Disability, Muscle Strength, and Functional Performance.

Background: Neuromuscular electrical stimulation (NMES) is widely used in the rehabilitation of knee osteoarthritis (KOA) to improve quadriceps activation and counteract arthrogenic muscle inhibition. However, randomized controlled trials (RCTs) have reported inconsistent findings, and the overall clinical effectiveness of NMES across key patient outcomes remains uncertain. Objective: To evaluate the effects of NMES, administered alone or in combination with exercise, on pain, self-reported disability, quadriceps muscle strength, and functional performance in adults with KOA, and to explore whether treatment effects differ according to comparator intervention. Methods: A systematic review and meta-analysis of RCTs was conducted according to PRISMA 2020. PubMed/MEDLINE, Embase, Scopus, Web of Science, and CENTRAL were searched from inception to April 20, 2026. Random-effects meta-analyses were performed using restricted maximum likelihood estimation. Prespecified subgroup and sensitivity analyses were undertaken, and risk of bias was assessed using the Cochrane RoB 2 tool. Results: Eight unique RCTs (10 publications) were included. Overall, NMES did not significantly improve pain, self-reported disability, quadriceps strength, or six-minute walk distance compared with pooled comparator interventions. A significant improvement was observed for Timed Up and Go performance, although this estimate was largely driven by a single trial. Prespecified subgroup analyses demonstrated that treatment effects differed according to comparator intervention. NMES combined with exercise resulted in greater pain reduction than exercise alone, whereas no consistent advantage was observed when NMES was compared with alternative conservative interventions. Most trials were judged to have low risk of bias or some concerns. Conclusions: NMES does not appear to provide consistent clinical benefits across all rehabilitation settings for KOA. Rather, its effectiveness depends on the therapeutic context in which it is delivered, with the greatest benefit observed when used as an adjunct to structured exercise rather than as a stand-alone intervention. Larger, methodologically rigorous RCTs using standardized stimulation protocols are required to define the patients most likely to benefit.