Percutaneous Electrolysis in Patients with Musculoskeletal Disorders: A Systematic Review

Varela-Rodríguez S^1*, Cáceres-Pajuelo JE² and Sánchez-Sánchez JL^1
*Correspondence: Varela-Rodríguez S, University of Salamanca, Donantes de Sangre Street, 37007, Salamanca, Spain, Email:

Keywords

Musculoskeletal disorders • Musculoskeletal pain • Percutaneous electrolysis • Galvanic electrolysis • Electric stimulation therapy • Systematic review

Introduction

Musculoskeletal disorders (MSDs) are one of the most prevalent groups of debilitating health conditions found globally and a major source of disability and lost work time [1-3]. Musculoskeletal pain is the most disabling symptom in MSDs, causing a high number of requests for healthcare treatments and rising social costs [4]. MSDs affect at least 100 million people in Europe, accounting for half of all European absences from work and for 60% of permanent work incapacity [5]. It is estimated that economic costs associated with musculoskeletal pain range from $261 to $300 billions [6,7]. More than a third of these health care costs are incurred by a small percentage of persistent utilizers [8].

Percutaneous electrolysis (PE) is a minimally invasive approach that consists in the application of a galvanic current transmitted through an acupuncture needle [9-11]. The technique involves a combination of mechanical and electrical stimulation. The needle is placed directly into affected soft tissue structures under ultra-sound visualization [12-14]. Galvanic current in a saline solution generates a chemical process of electrolysis, which causes the dissociation of molecules of sodium chloride and water and produces a non-thermal electrochemical ablation [15-17]. This organic reaction can stimulate localized inflammatory response and promote wound healing in damaged and/ or degenerated tissue [13,16,18].

Although several mechanisms and effects are attributed to PE, currently there are only a few publications that delve into this topic. The application of PE in collagenase-induced tendinopathy in rats produces an increase in anti-inflammatory and angiogenic molecular mechanisms [18]. Similar results are found in notexin-induced muscular injury in rats, with a decrease in proinflammatory mediators and an increase in the expression of anti-inflammatory proteins and vascular endothelial growth factor [16]. In healthy humans, this technique causes a greater parasympathetic activity (detected by hearth-rate variability) due to the combination of needle puncture and electric current [9,10].

The aim of this review was to gather and analyse the present evidence related to the effectiveness of PE on pain and disability in the treatment of MSDs. This review article is one of the first systematic reviews related to PE that includes an analysis of methodological quality and risk of bias.

Literature Review and Methodology

This systematic review was conducted in accordance with the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement and it was registered on the International prospective register of systematic reviews (PROSPERO) with number CRD42020181168 [19].

Articles were included based on the following criteria: (1) Randomized controlled trials conducted on human subjects over 18 years old; (2) Published in English or Spanish; (3) Patients with non-specific MSDs, without underlying medical causes; (4) At least one group included intervention with PE, either in isolation or combined with other treatments (physiotherapeutic or multidisciplinary); (5) Comparison with at least one other group that did not receive PE; and (6) Outcome measure for pain and/or function. The exclusion criteria were: (1) Animal studies; (2) Poorly identified outcomes; and (3) Pain related to specific medical causes (e.g. Tumor, rheumatoid arthritis, fractures, hemiplegia, etc.).

Electronic literature searches were conducted on PubMed, PEDro, CINAHL, MEDLINE, Scopus, Web of Science, Cochrane Library and ScienceDirect. It was performed from database inception to April 17, 2020. The search strategy combined different terms related to the study intervention: ("percutaneous electrolysis" OR "percutaneous needle electrolysis" OR "intratissue percutaneous electrolysis" OR "galvanic electrolysis"). These keywords were identified after preliminary searches and the strategy was adapted to each type of database.

After removing duplicates, title and abstract of the articles were screened for eligibility. Then, the full-text document of the selected studies was assessed against the inclusion and exclusion criteria. When the eligibility of the abstract document was unclear, the full-text study was also reviewed. This process was performed by two independent researchers and disagreements were resolved by consulting a third reviewer.

Two independent authors extracted data from each included article using a standard form containing the following information: title, authors, year, country, journal, aim of study, population, diagnosis, groups, type of PE, followup period, outcome domain, outcome measurement, results, conclusions, limitations, and methodological quality. A third author participated in the process in case of discrepancy between both reviewers.

It was expected that there would be heterogeneity in diagnosis, interventions, comparisons and outcomes. In consequence, the findings of the selected studies were synthesized in a narrative format. The data extracted were summarized for presentation in this document providing information about the study, participants, interventions, follow-up, outcome measures and results (differences between groups).

Risk of bias was assessed through the Version 2 of Cochrane Collaboration's Risk of Bias tool for randomized trials (RoB 2). The RoB 2 tool is structured into five bias domains: randomisation process, deviations from intended interventions, missing outcome data, measurement of the outcome and selection of the reported result. According to the answers to signalling questions, each domain is evaluated as “low risk of bias”, “some concerns” and “high risk of bias”. Overall risk of bias judgment was based on the assessments of the other domains [20].

Furthermore, methodological quality of the included studies was assessed against the Physiotherapy Evidence Database (PEDro) scale [21]. The PEDro scale is based on 11 criteria: (1) inclusion criteria and source, (2) random allocation, (3) allocation concealment, (4) baseline comparability, (5) blinding of subjects, (6) blinding of therapists, (7) blinding of assessors, (8) over 85% follow-up, (9) intention-to-treat analysis, (10) between-group comparison, and (11) point estimates and variability [22]. Only the last 10 items are scored with 1 or 0 points, whether the trial meets the criteria or not, respectively. Therefore, the maximum PEDro score is 10 points. When the score was at least 5 points, the study was considered to be of moderate to high quality [21].

Both risk of bias and methodological quality assessments were conducted by two independent reviewers and Kappa concordance index was calculated between them. The differences were resolved by consulting a third researcher.

Results

Study selection

A total of 175 results were obtained by searching specialized databases. After duplicate records were eliminated, 65 articles were screened by title and abstract. At this point, 51 studies were excluded for not meeting inclusion criteria, leaving 14 articles for full-text analysis. In this last step, another 7 studies were excluded for the following reasons: no comparison group, no randomization or no full-text available [12,13,17,23-26]. Finally, 7 studies were selected to be included in the review [27-33]. Study selection flow diagram is displayed in Figure 1.

Study characteristics

The main characteristics of the articles included in this systematic review are exposed in Table 1. The included studies were published between 2015 and 2018. A total of 407 patients participated in the trials, of which 194 subjects received PE intervention. Most studies involved the general population and both sexes, with ages ranging from 18 to 65 years. Only one study limited the inclusion criteria to non-professional male soccer players aged 18-35 [33].

MSDs diagnoses consisted of patellar tendinopathy, subacromial syndrome, chronic plantar heel pain, acute whiplash syndrome, temporomandibular myofascial pain and adductor longus enthesopathy-related groin pain [27-33]. Acute whiplash syndrome was the pathology studied with the largest sample number (n = 100) [31]. Subacromial syndrome was the only MSD enrolled in two trials with a total number of 86 patients [28,29]. The smallest sample corresponded to the trial investigating adductor longus enthesopathyrelated groin pain (n = 24) [34]. Most of the included musculoskeletal pain presented a time of evolution greater than 1 month, with the exception of acute whiplash syndrome and adductor longus enthesopathy which was not specified [31,33].

The parameters employed for the application of PE are different, but two groups can be identified, so that four studies use high intensity (ranging from 2 to 4 mA) in short times (usually 3 seconds) and three studies low intensity (< 1 mA) with long times (generally > 1 minute) [27-33]. Regarding to the target tissue, four studies applied this technique on tendon, two on muscle and one on the plantar fascia [27-33].

PE intervention was associated with an active exercise program in five studies [27,28,30,32,33]. On one occasion it was combined with exercise and manual therapy and in only one study it appeared isolated without any other intervention [29,31].

The most frequently comparison was the same intervention as the experimental group but suppressing PE [28,29,33]. In other studies, it was compared with another intervention, usually conventio nal physiotherapy, or with a sham intervention [27,30,31]. One study used two comparison groups that included deep dry needling and a sham needling intervention [32].

All selected studies included outcome measurements for both pain and disability with the exception of the trial carried out by Abat et al. which only includes scales for disability [27]. Pain was assessed in different situations but only two scales were used, so that four studies used the 11-point Numeric Pain Rating Scale (NPRS-11) and two the Visual Analog Scale (VAS) [28-33]. However, the variability of outcome measurement tools for disability is much more diverse and specific questionnaires are used for each pathology: Victorian Institute of Sports Assessment for Patellar tendon (VISA-P), Disabilities of the Arm, Shoulder and Hand (DASH), Shoulder Pain and Disability Index (SPADI), Northwick Park Neck Questionnaire (NPQ), 21-item activities of daily living subscale of the Foot and Ankle Ability Measure (21-ADL of FAAM), temporomandibular joint (TMJ) functionality test, Patient Specific Functional Scale (PSFS) [27-33].

Measurements periods varied from immediate post-intervention to 6 months follow-up. Three studies conducted a short-term follow-up, obtaining the last measurements within 2 weeks after the end of treatment [27,28,31]. The remaining studies presented a longer follow-up, with assessments over 70 days post-intervention and even 6 months after the last treatment session [29,30,32,33].

Three studies showed greater improvements in pain with PE intervention, whereas García-Naranjo et al. found no difference between groups but concluded that the results supported PE intervention as it was more costeffective than the comparison intervention (standard physiotherapy) [28-31]. Other trials presented less conclusive results. Moreno et al. find differences in favour of PE for pain upon contraction but not upon palpation [33]. Furthermore, López-Martos et al. obtained significant differences when PE was compared to sham intervention, but not when it was compared to deep dry needling [32].

Similar results were found in the assessment of disability, with significant differences in favour of PE intervention in three of the included studies [28,30,32]. In the same way as in the evaluation of pain, Garcia-Naranjo et al. concluded that there were no differences between groups, which benefited PE for being more cost-effective [31]. Abat et al. did not examine function without making subgroups, but the disability assessment was employed for a survival analysis, showing a greater heal rate in PE group [27]. However, Moreno et al. found no difference between groups when comparing PE plus active exercise with only active exercise [33]. On the other hand, de Miguel-Valtierra et al. observed greater improvements with PE intervention in SPADI questionnaire but not in DASH questionnaire [29].

Methodological quality

Table 2 represents the details of the assessment obtained by each study in each of the PEDro scale criteria (Kappa index of 0.752). All included studies scored at least 6 points on the PEDro scale, demonstrating moderate to high methodological quality. The mean score of the studies evaluated was 7 points, ranging from 6 to 8 points. The criteria for blinding of subjects and therapists were not met by any of the studies. However, López-Martos et al. performed a sham needling intervention and Fernández-Rodríguez et al. attempted to blind both subjects and therapist, but were considered not to meet the criteria because patients can feel some pain when electrolysis is applied and the treatment can be recognized [30,32]. On the other hand, the blinding of the assessors was deemed valid in four studies, although it must be taken into account that the outcome measures were carried out by patient-reported questionnaires in which the subjects can be considered their own assessor and they were unblended [27,29,31,33].

Risk of bias

Overall bias judgement for most of the included studies was assessed as “high risk”, with the exception of two studies which showed “some concerns” [29,33]. The greatest risk of bias corresponded to the measurement of the outcome, since pain and disability were assessed by patient-reported questionnaires and may be affected by the fact that the subjects were unblinded. Selection of the reported result was usually evaluated as “some concerns” due to trial protocols were found only for two studies [28,29]. All other biases were generally judged as “low risk”, excluding the study conducted by Fernández- Rodríguez et al. More details of risk of bias assessment are provided in Table 3. Kappa concordance index was 0.749 [30].

Discussion

This systematic review aimed to investigate the possible effects of PE on pain and disability in patients with MSDs. In order to gather the best available evidence, only randomised clinical trials were selected. A qualitative analysis of the included studies was performed, but a meta-analysis was not possible due to the high heterogeneity of the trials, related to the variety of pathologies, comparisons, PE application parameters, follow-ups or outcome measures.

Although it is difficult to generalize the results of this review due to the heterogeneity and low number of included studies, we consider that PE appears to be an effective treatment intervention for the improvement of pain and disability in patients with MSDs. Most studies found significant differences in favour of the group that involved PE intervention. However, some studies presented inconsistent results and detect no significant differences for some outcome measurements.

Two studies combined PE intervention with active exercise and compared it to exercise alone, so one found differences in favour of the PE group but in the other study the results were inconsistent and showed no long-term difference in disability [28,33]. De Miguel-Valtierra et al. obtained favourable results for pain when PE was added to manual therapy and exercise treatment, but the outcomes for disability were contradictory [29]. Nevertheless, PE seems to be a good complement to other treatments.

A sham needling intervention was used as a comparison to PE by two studies in which the results were favourable to PE group [30,32]. In one of them, PE was also compared to dry needling, but in this case the differences were only reported in some follow-up time-points [32]. Therefore, the effectiveness of PE is greater than that of sham intervention, whereas more studies comparing PE to dry needling are needed.

Two other studies compared PE to standard treatment. Garcia-Naranjo et al. found no difference between the two treatments even though the frequency of sessions and total cost of treatment was much lower in PE group, while Abat et al. even showed better results for PE intervention [27,31]. Consequently, PE could be a more cost-effective alternative to standard physiotherapy.

It should be noted that none of the selected studies used a non-intervention control group, so it is not known what part of the results can be attributed to the natural evolution of the pathology.

Although the included studies presented from moderate to high methodological quality, the results should be treated with caution due to the high risk of bias. The difficulty of blinding the subjects greatly limited the validity of the outcome measurements. In addition, the review was focused on the effects on pain and disability, and these were evaluated using selfreported questionnaires, so the assessment should only be considered completely blinded when the subjects were also blinded. As previously described, Fernández-Rodríguez et al. and López-Martos et al. enrolled a sham intervention group, but patients would probably be able to identify the PE intervention because the application of galvanic current produces some pain [30,32]. Reviewing the literature related to invasive physiotherapy, the true blinding of participants was achieved in the study conducted by Mayoral et al. in which patients received the interventions under general anesthesia [35].

The number of publications that explore in depth the mechanisms of PE is still limited and the studies with the highest impact are performed on animal models [16,18]. The exact therapeutic mechanisms are not completely defined, and both mechanical and biochemical effects are suggested [29]. Most of the selected trials were conducted in chronic MSDs and it has been proposed that in these conditions PE promotes a local inflammatory response, inducing phagocytosis and subsequent tissue repair [13]. Moreno et al. investigated an acute injury and exposed that phagocytic activation could also favour these pathologies, besides the stimulation of the vascularization and the reduction of the inflammatory mediators [16,33]. Recently, it has been hypothesized that other needling techniques may produce neurophysiological effects integrated into a pain neuroscience paradigm, such as activation of central inhibitory pain pathways, hyperstimulation analgesia, conditioned pain modulation, segmental inhibition or release of endogenous opioids and other neurotransmitters [36-38]. Future studies should investigate the influence of PE on these mechanisms.

Valera-Garrido and Minaya-Muñoz have suggested that the effects of PE depends on the application parameters, so that high intensity and short time modality generates a greater inflammatory response, while low intensity and long-time method produces a larger analgesic effect [11]. However, we are not aware of any randomized clinical trial comparing both application modalities in patients with MSDs. Therefore, further research is also needed to generate treatment protocols and standardize application parameters.

Conclusion

To the best of our knowledge, this is one of the first systematic reviews to investigate de effectiveness of PE in the management of MSDs. Only randomized clinical trials were included and the assessment of risk of bias and methodological quality were performed with good concordance between reviewers. Nevertheless, this study suffered from several limitations that should be mentioned. As described above, the high heterogeneity of the selected studies hindered the analysis and discussion of the results. In addition, the number of trials was small and included only six pathologies with different etiologies, complicating the generalization to the rest of MSDs. Another potential limitation is the impossibility of conducting a meta-analysis that would have provided objectivity to the results.

Conflict of Interest

The authors declare that there is no conflict of interest.

Funding

This review study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

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