Electrical stimulation modalities for patellofemoral pain: a systematic review and meta-analysis

Patellofemoral pain (PFP) is a common knee disorder associated with persistent pain and functional limitations. Electrical stimulation modalities have been proposed as adjuncts to exercise-based rehabilitation; however, their effectiveness may differ according to modality and therapeutic target. This systematic review and meta-analysis evaluated the effects of different electrical stimulation modalities on pain, knee function, and muscle-related outcomes in adults with PFP. This systematic review was prospectively registered in PROSPERO (CRD420251108421) and conducted in accordance with the PRISMA 2020 statement. PubMed, Web of Science, Scopus, and Embase were searched from inception to June 2026 for randomized controlled trials evaluating electrical stimulation interventions in adults with PFP. Risk of bias was assessed using the Cochrane Risk of Bias 2 tool, and certainty of evidence was evaluated using the GRADE approach. Random-effects meta-analyses were performed when studies were sufficiently comparable, using mean differences (MDs) with 95% confidence intervals (CIs). Twenty-six randomized controlled trials involving 1,217 participants evaluated seven electrical stimulation modalities. NMES was investigated in 13 trials, EMS in five, and the remaining modalities in one or two trials each. Quantitative synthesis was conducted only for outcomes with sufficient clinical and methodological comparability. Compared with exercise-based rehabilitation, sham stimulation, or other prespecified control interventions, NMES was associated with reduced pain (MD = − 0.59, 95% CI: −0.94 to − 0.23; P < 0.01; I² = 52%) and improved knee function measured by the Anterior Knee Pain Scale (MD = 5.24, 95% CI: 3.00 to 7.47; P < 0.01; I ² = 0%). The certainty of evidence for these outcomes was low. EMS showed a nonsignificant reduction in pain (MD = − 0.56, 95% CI: −1.69 to 0.57; P = 0.33; I ² = 48%), with low-certainty evidence. Individual studies also reported improvements in quadriceps strength and muscle activation following NMES. Evidence for TENS, HVPGS, PST, RFD, and tDCS was limited by the small number of trials, heterogeneous protocols, and differences in comparators and outcomes, precluding robust quantitative comparisons. Low-certainty evidence suggests that NMES may provide modest short-term benefits for pain and knee function when used as an adjunct to rehabilitation in adults with PFP. The evidence does not establish NMES as superior to other electrical stimulation modalities. Evidence for EMS remains uncertain because the pooled effect on pain was not statistically significant, while evidence for other modalities is currently insufficient to determine their effectiveness. Electrical stimulation should therefore be considered a targeted adjunct to, rather than a replacement for, exercise-based rehabilitation. Further adequately powered randomized controlled trials with standardized stimulation protocols and longer follow-up are needed to determine sustained effects and identify patients most likely to benefit.