Introduction: Chronic low back pain (CLBP) is the leading cause of years lived with disability worldwide. Transcutaneous electrotherapies, encompassing low and medium-frequency sensory and motor nerve stimulation, have been widely used to treat CLBP but, with the partial exception of transcutaneous electrical nerve stimulation (TENS), their effect on pain, disability, quality-of-life, and psychosocial outcomes have not been systematically reviewed. Additionally, the difference in efficacy between stand-alone and mixed interventions is unclear. The purpose of this systematic review and meta-analysis was to clarify the overall effect of transcutaneous electrotherapies on self-reported outcomes in CLBP patients.
Methods: Four databases (PubMed, Scopus, Web of Science, Embase) and two study registries (WHO International, US National Institute of Health) were searched. Articles that utilized transcutaneous electrotherapies as a primary intervention for CLBP and compared it against active or passive controls were included. CLBP was defined as pain of at least 12 weeks duration between the lower ribs and gluteal fold with or without leg pain, excluding participants diagnosed with a specific spinal pathology, with mixed lower-upper back pain, and <18y or > 70y old. Two reviewers independently extracted study data and assessed risk of bias. Studies were grouped by intervention vs comparison, and by time of follow-up. Meta-analyses were conducted where appropriate.
Results: 3939 records were screened and 89 full-text reports were assessed for eligibility. Fourteen studies were included in the qualitative review and 6 in the meta-analyses. Pain outcomes: meta-analyses revealed no significant difference for TENS vs. active control [SMD = 0.43, 95% CI = -0.67, 1.53], TENS vs. passive control [SMD = -0.36, 95% CI = -1.21, 0.49], or mixed TENS vs. active control [SMD = -0.04, 95% CI = -0.86, 0.77] at post-intervention, nor any significant differences in mixed TENS vs. active control at 1-month post-intervention [SMD = 0.61, 95% CI = -0.03, 1.24]. Interferential current (IFC) was more effective than active control (2 studies), while electromyostimulation (EMS) was generally superior to passive, but not active, controls (6 studies). Disability outcomes: meta-analyses revealed no significant difference for TENS vs. active control at post-intervention [SMD = 0.60, 95% CI = -0.57, 1.76], mixed TENS vs. active control at post-intervention [SMD = 0.24, 95% CI = -0.37, 0.84], or mixed TENS vs. active control at 1-month post-intervention [SMD = 1.04, 95% CI = -0.36, 2.43]. IFC was more effective than active control (2 studies), while the comparative benefit of EMS was mixed (6 studies). We were unable to perform meta-analyses for IFC and EMS studies, nor for quality-of-life or psychosocial outcomes, due to an insufficient number of comparisons.
Discussion: There is moderate evidence that TENS is similar to active and passive controls for improving pain and disability, and limited evidence that IFC is superior to active controls for improving pain and disability. There is limited evidence that EMS is superior to passive but not active controls for improving pain, and similar to all controls for improving disability. There is inconclusive evidence regarding the effect of transcutaneous electrotherapies on quality-of-life and psychosocial outcomes.