EFFECTIVENESS OF TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION (TENS) IN THE MANAGEMENT OF CHRONIC MUSCULOSKELETAL PAIN: A SYSTEMATIC REVIEW OF RANDOMIZED CONTROLLED TRIALS AND PRIMARY STUDIES

Abstract

Introduction: Chronic musculoskeletal pain (CMP) is one of the leading causes of global disability, affecting more than 1.71 billion individuals worldwide and constituting a major burden on healthcare systems. Transcutaneous Electrical Nerve Stimulation (TENS) is a widely utilized, non-invasive electrophysical modality that delivers low-voltage electrical current through cutaneous electrodes to modulate nociceptive transmission and activate endogenous analgesic mechanisms. Despite its broad clinical adoption, heterogeneity in study designs, patient populations, stimulation parameters, and outcome assessments has generated controversy regarding its efficacy. This systematic review aims to synthesize evidence from primary studies investigating TENS efficacy across multiple musculoskeletal pain conditions, addressing the existing research gap on comparative effectiveness across diverse outcomes including pain intensity, physical function, quality of life, analgesic consumption, and psychosocial parameters. Methods: The study strictly adhered to the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) 2020 guidelines. Inclusion criteria encompassed primary studies (randomized controlled trials, cohort studies, case-control studies, cross-sectional studies, observational prospective and retrospective designs) evaluating TENS as an intervention in adults with chronic musculoskeletal pain. Studies were independently screened by two reviewers using PRISMA 2020 guidelines. Risk of bias was assessed using the Cochrane RoB 2.0 tool for RCTs and ROBINS-I for non-randomized studies. Data were extracted on pain intensity (VAS/NRS), physical function (WOMAC, TUG, 6MWT), quality of life (SF-36), analgesic consumption, and adverse events. Results:  15 RCTs met inclusion criteria. Studies encompassed diverse musculoskeletal conditions including knee osteoarthritis (n=8), fibromyalgia (n=4), chronic neck pain (n=2), hemiplegic shoulder pain (n=1), chronic non-cancer pain (n=1), pudendal neuralgia (n=1), and subacute spinal spasticity (n=1). Active TENS demonstrated statistically significant superiority over sham/placebo TENS in reducing pain intensity (VAS/NRS) in the majority of studies, with standardized mean differences (SMD) ranging from -0.51 to -1.96. Functional outcomes including WOMAC scores, TUG test, and 6MWT showed meaningful improvements in TENS-treated groups across multiple conditions. Reduction in analgesic consumption was observed in several studies. Adverse events were minimal, generally mild, and predominantly local (skin erythema). Across 10 predefined outcome domains, TENS consistently demonstrated clinically meaningful effects in pain intensity reduction, movement-evoked pain, fatigue reduction, physical performance, and patient global impression of change. Discussion: The evidence synthesized in this review supports TENS as an effective, safe, and clinically applicable non-pharmacological modality for chronic musculoskeletal pain management. Efficacy was most robust for conditions involving peripheral nociceptive mechanisms including knee osteoarthritis and fibromyalgia. Optimal TENS parameters remain heterogeneous across studies; however, high-frequency TENS (80–100 Hz) and modulated-frequency protocols (2–125 Hz) demonstrated consistent analgesic effects. Combination with physiotherapy exercise programs and patient education enhanced outcomes. Methodological limitations include small sample sizes, short follow-up durations, and challenges in blinding participants to active TENS. Wearable and home-use TENS devices showed non-inferiority compared to weak opioids with superior safety profiles. Conclusion: TENS is an effective, safe, and guideline-concordant non-pharmacological intervention for chronic musculoskeletal pain. It significantly reduces pain intensity and improves physical function and quality of life while minimizing analgesic dependence. TENS should be considered as a first-line adjunctive modality in multimodal rehabilitation programs for chronic musculoskeletal pain.