Effects of monopolar pulsed-capacitive dielectric radiofrequency diathermy in patients with chronic low back pain: a randomised clinical trial

Monopolar capacitive diathermy is a physiotherapy technique that uses high-frequency currents to generate heat in deep tissues. This heat can have several therapeutic effects, especially in the treatment of chronic low back pain (CLBP), however, until now there is little evidence of this type of diathermy. The purpose was to evaluate the efficacy of a pulsed monopolar dielectric radiofrequency diathermy (PRF)-capacitive type versus simulated treatment on symptomatology of patients with CLBP. A single-blind randomised controlled trial was conducted. Sixty patients with CLBP were randomly assigned to a PRF-capacitive or a simulated treatment group. All participants received 3 sessions per week for 3 weeks. Disability, pain intensity, movement phobia, lumbar anteflexion, quality of life, and sleep quality were assessed at baseline, after treatment, and at two months. The application of 9 sessions of PRF-capacitive showed significant improvements compared to simulated therapy during the entire follow-up for disability (F = 26.99, p < 0.001), pain intensity (F = 0.550, p < 0.001), the quality of life components of physical function (F = 0.780, p < 0.001), social function (F = 0.780, p < 0.001) and mental health (F = 0.858, p = 0.003) and for sleep duration (F = 0.863, p = 0.004).


Participants
A total of 68 patients aged between 18 and 65 years, diagnosed with CLBP of more than 3 months duration and with a pain intensity of at least 3 points, were studied between March 2022 and October 2022 through an advertisement displayed on social networks.The study was conducted at the Clinical Physiotherapy Unit of the Faculty of Health Sciences of the University of Almeria.Patients were assessed and enrolled in this study if they met the following selection criteria.
Inclusion criteria • Men and women between the ages of 18 and 65.
• Diagnosed by a specialist CLBP physician.
• 3 or more in pain intensity by Visual Analog Scale (VAS).
• Acceptance and signature of informed consent for voluntary participation in the research study.
• Not undergoing any type of physical therapy or pharmacological treatment.
• Acceptance to attend 90% of the treatment sessions.

Exclusion criteria
• Undergoing rehabilitation or pharmacological treatment for the pathology of lumbar origin.
• Participants could not have previously received diathermy treatment, in any of its types (capacitive or resis- tive).• Alterations in sensitivity or coagulation.
• Presence of osteosynthesis material at lumbar level.
• Patients who have recently undergone radiotherapy.
• Non-acceptance of informed consent or non-attendance at more than 90% of the treatment sessions.

Outcome measures
At the start of the study, all participants provided clinical and demographic data such as age, sex, weight, height, education and clinical presentation of symptoms, and completed a series of self-report measures.Physical examination was performed by a blinded assesor who was unaware of the participants' treatment assignment.Outcome measures were assessed before randomisation (baseline assessment), immediately after treatment (1 day after the last intervention) and at two months after the end of the intervention (short-term follow-up) (Fig. 1).
A 30% improvement was considered a useful threshold to identify a clinically meaningful improvement in each of the measures 33 .
Primary outcome measures -Roland Morris Disability Questionnaire (RMDQ): This questionnaire consists of 24 items that rate limitations in different activities of daily living attributed to low back pain, such as walking, bending, sitting, lying down, dressing, sleeping, self-care and activities of daily life.Disability is rated from 0 points (best) to 24 points (worst) 34 .
-Visual Analogue Scale (VAS): assesses pain intensity with a score from 1 to 10, where the highest pain is 10 35 .
Each item is scored on a four-point Likert scale ranging from "strongly disagree" 1 to "strongly agree" 4 .The total score ranges from 17 to 68 points 36 .

Follow-up
Participants will complete follow-up assessment at 3 weeks (1 day after the last intervention) and 2 months following baseline assessment with a blinded researcher.
Loss to follow-up (n = 2) Loss to follow-up (n = 1) Loss to follow-up (n = 2) Informed Conset Form

PRF-capacitive group
Patients in a prone position received a pulsed emission of 840 KHz and 30v dynamically on the active myofascial trigger points of the following muscles of the lumbar area.

Simulated control group
Simulated treatment consisting of the same execution protocol as the experimental group, but with the device turned off.The intervention was simulated for 20 minutes.

Analysis of the benefits of each of the interventions
Patients with chronic non-specific low back pain screened for eligibility (N = 98) Loss to follow-up (n = 3)   • Pittsburgh sleep quality index (PSQI) 10-item questionnaire with a total of 19 questions related to sleep habits in the previous month.The questions are divided into 7 areas, each with a score between 0 and 3 points.The overall score ranges from 0 (no difficulty sleeping) to 21 points (severe difficulty sleeping) 38 .

• McQuade test
This test assesses the isometric strength of the trunk flexor muscles.The patient is placed in the supine position and asked to flex the head and shoulders until the scapula is lifted off the table.The number of seconds they hold this position is recorded, the maximum being 120 s 39 .• Anterior trunk flexion Measures lumbar mobility in trunk flexion from a standing position.Standing up with the legs streched out, the subject is asked to lean forward and try to touch the ground, stopping when pain or limitation of movement appears.The distance between the toes and the ground is measured in centimetres 40 .

Sample size
The sample size was based on estimates established by Willian 41 .The calculations were based on the detection of 2.5 point differences in RMDQ score (minimum clinically important difference), assuming a standard deviation of 2.5 points, a 2-tailed test, an alpha (α) of 0.05 and an objective power (beta) of 85%.The estimated sample size was 60 subjects (30 per group).

Randomisation
After the initial assessment, participants who met the eligibility criteria were randomised in a 1:1 ratio to receive either (i) high-frequency therapy using PRF-training signals on myofascial trigger point symptomatology or (ii) simulated control treatment.Both groups were treated by two physiotherapists with more than 10 years of experience in managing people with CLBP.Hidden allocation was performed using a computer-generated random table of numbers created prior to the start of data collection by a researcher who was not involved in patient recruitment or treatment.Sequentially numbered individual tokens were prepared with the random allocation.The cards were folded and placed in sealed opaque envelopes.Another therapist, blinded to the initial examination, opened the envelope and proceeded with treatment according to group assignment.The outcome assessor and study statistician were blinded throughout.The computer-generated outcome measures transmitted to the statistician contained no information identifying the group assigned to each patient.

Interventions
After the randomisation, consenting participants were placed randomly into two groups to receive PRF-capacitive or simulated treatment.All participants received 3 sessions per week for 3 weeks, for a total of 9 sessions.Patients in both treatment groups had to undergo at least 90% of their scheduled treatment sessions to be considered and remain in the intention-to-treat analysis.The nature of the intervention did not allow for the blinding of the physiotherapist and participants.No kinesiotherapy was administered in any group and no self-administered therapeutic exercise was administered.Potential adverse effects were to be reported to the principal investigator.Details of the interventions are provided below.

PRF-capacitive group
The experimental group underwent a PRF-capacitive application using the Physicalm® device (Biotronic Advance Develops SL, Granada, Spain).Patients in a prone position received a pulsed emission of 840 kHz and 30v dynamically (rotational and translational movements) on the active myofascial trigger points of the following muscles of the lumbar area: lumbar quadratus lumborum, multifidus and iliocostalis.The time per session was 20 min, 3 sessions were carried out per week for 3 weeks, on Mondays, Wednesdays and Fridays, in total 9 treatment sessions.

Simulated control group
The control group was administered a simulated treatment consisting of the same execution protocol as the experimental group, but with the device turned off.The intervention was simulated for 20 min.Three sessions were carried out per week for three weeks, on Mondays, Wednesdays and Fridays, for a total of nine treatment sessions.Once the simulated intervention period was over and follow-up data was collected, a washout period was established and the same treatment was given as for the experimental group.

Patient and public involvement statement
Patients were not involved in the design, or conduct, or reporting, or dissemination plans of our research.

Data analysis
The IBM SPSS© version 28.0 software package was used for statistical analysis.A p-value < 0.05 was considered statistically significant.After a descriptive analysis, the normal distribution of the variables was tested using the Kolgomorov-Smirnov test.Baseline demographic and clinical variables were compared between the two groups using χ2 tests for categorical data and Student's t-tests for continuous data.Repeated measures analysis of variance (2 × 3 mixed model ANOVA) was used to analyse time effects between both groups (PRF-capacitive versus simulated) and group interaction effects for all outcome measures (RMDQ, and VAS as primary outcome), www.nature.com/scientificreports/ between immediately after treatment and two months later.Changes in variable scores within and between groups were measured by 95% confidence interval t-tests for paired or independent samples, as appropriate.

Baseline characteristic
For this randomized trial, a total two hundred and fifty (n = 250) patients with LBP were screened for eligibility.
Reasons for exclusion are shown in Fig. 1-a patient recruitment and inclusion flow chart.Sixty patients (mean age ± SD: 48.5 ± 9.2; 53.3% male) met the inclusion criteria and were randomized to receive treatment with either PRF-capacitive (N = 30), or simulated therapy (N = 30).There were no significant differences between the two groups at baseline in terms of demographics shown in Table 1.All patients who participated did not receive any other treatments during the process of the study.The Kolmogorov-Smirnov test showed the normal distribution of the numerical variables.
When analysing the two groups, the PRF-capacitive group showed greater changes from baseline between the third week and the second month: RMDQ (post: 5.37, p < 0.001; follow-up: − 0.57, p < 0.030) and ODI (post: 17.27, p < 0.001; follow-up: − 0.93, p < 0.37), by contrast, the simulated group changes were not as significant at two months for ODI (follow up: − 0.2, p = 0.327).

Pain intensity
The 2 × 3 mixed ANOVA did not reveal a significant difference between the VAS scores of both groups (F = 0.550, p < 0.001).At 3 weeks post-treatment, the groups revealed differences in pain intensity (F = 0.617, P < 0.001), where the PRF-capacitive group displayed a greater decrease.No significant differences between the groups were found at the two-month follow-up (Table 2).
During the analysis of the groups, the score change in pain intensity was significantly greater in the PRFcapacitive group than in the simulated group at 3 weeks post-treatment: the PRF-capacitive group (post: 3.67, p < 0.001), the simulated group (post: 1.88, p < 0.001).Nonetheless, the decrease in pain was similar in both groups at the 2-month follow-up.

Kinesiophobia
The ANOVA analysis did not indicate statistically significant differences between the groups for kinesiophobia.However, analysis did show statistically significant differences between the groups at all follow-up periods (post: F = 0.891, p < 0.001; follow-up: F = 0.693, p < 0.001).

Quality of life
Regarding the quality of life, the 2 × 3 mixed-model ANOVA with repeated measurements analysis showed significant time * groups interaction for physical function (F = 0.780, p < 0.001), social function (F = 0.780, p < 0.001), and mental health subscales (F = 0.858, p = 0.003).During the group analysis, significant differences for the following subscales of quality of life on the SF-36 appeared between week 3 of post-treatment evaluation [body pain (F = 3.100, P = 0.023), and emotional role (F = 53.003,p = 0.002)], and at the two month's evaluation [social function (F = 29.234,p < 0.001), and emotional role (F = 37.563, p = 0.004)].Table 3 shows the differences between the groups for these results.

Physical outcomes
Similarly, no statistically significant ANOVA results were achieved for the McQuade test and fingertip-to-floor distance.However, analysis of the groups showed statistically significant differences at 3 weeks post-treatment and the 2 months follow-up: in the McQuade test (post: F = 3.105, p = 0.012; follow-up: F = 1.014, p = 0.022) and in the Table 3. Changes baseline, post treatment, and two months follow-up of quality of life SF-36.Values are expressed as mean ± standard deviation for immediate post-treatment, and two months follow up, and as mean (95% confidence interval) for between-group change scores.*p ˂ 0.05 significant ANOVA adjusted from baseline values for differences among groups.Significant values are in bold.After treatment, the fingertip-to-floor distance decreased 5.93 cm in the group that received PRF-capacitive treatment and − 0.26 cm in the simulated group.The results were maintained at the follow-up in both groups (see Table 2).

Discussion
We set out to conduct a unique study to evaluate the efficiency of PRF-capacitive treatment with 840 kHz pulsed emission and 30v in patients with non-specific CLBP at immediate and short-term follow-up compared to a simulated control group.The main discovery was that the application of 9 sessions of PRF-capacitive application was as effective at 3 weeks post-intervention as it was in a two-month follow-up for the improvement of disability, kinesiophobia, isometric abdominal muscle endurance, lumbar anteflexion mobility, quality of life, and quality of sleep.However, pain intensity only obtained statistically significant results at 3 weeks post-intervention, but not at the two-month follow-up.
Although hyperthermia has been used for years for different musculoskeletal pathologies, such as low back pain 21,22,42,43 , myofascial pain syndrome, shoulder pain 44,45 , cervical pain 46 , or patellofemoral pain 47 , with all these studies finding similar findings to ours in pain intensity and disability, to date the therapeutic effects of the capacitive mode in chronic low back pain have not been examined in depth.In a study by Notarnicola et al. 21in patients with chronic low back pain, the authors applied the capacitive and resistive radiofrequency mode or also Table 4. Changes baseline, post-treatment, and two months follow-up of quality of sleep.Values are expressed as mean ± standard deviation for immediate post-treatment, and two months follow up, and as mean (95% confidence interval) for between-group change scores.*p ˂ 0.05 significant ANOVA adjusted from baseline values for differences among groups.Significant values are in bold.www.nature.com/scientificreports/called TECAR therapy, obtaining significant differences in pain and disability in all follow-up periods.In contrast to our study, in this study, pain also obtained significant results at follow-up.The differences may be due to the fact that the authors applied radiofrequency in patients who, in addition to low back pain, had documented disc disease or disc herniation.Another difference with our study is that VAS was used indistinctly for leg or low back pain, which does not allow us to compare the results of pain intensity with those of our study.In addition, other studies on the knee joint have found improvements in function compared to a simulated control group.Similarly, a recent study in low back pain found that after diathermy intervention, pain intensity and muscle stiffness were significantly lower, with the difference that this study only applied the resistive mode 42 .
Based on the available evidence, the improvement we found with PRF-capacitive pain and disability may derive from the biological effects induced by hyperthermia.Deep tissue heating may reduce pain by promoting vasodilatation and outflow of pain mediators from the affected tissue, inhibiting nociceptive transmission by activation of A-alpha and A-beta fibres or stimulating cutaneous thermoreceptors 48 .Furthermore, muscle spasm due to musculoskeletal pain is often reduced by heat and this, in turn, may contribute to improved joint function, and thus disability 27,49,50 .
Regarding the increase in the isometric resistance of the thoracolumbar musculature and the range of movement in lumbar anteflexion.Although, other studies have found similar results applying radiofrequency to other joints 27,46 , such as Alguacil-Diego et al. 46 , who found an increase in the ROM of the right rotation of the cervical spine at 8 sessions, and Albornoz-Cabello et al. 27 who obtained an 18° increase in knee flexion in patients with patellofemoral pain syndrome.However, evidence evaluating the effect of radiofrequency diathermy on the range of motion is scarce.It is possible that the increase in range of motion may be related to an increase in tissue elasticity after radiofrequency diathermy, given that soft tissues that are heated before stretching maintain elongation after stretching, as well as requiring less force from the patient to achieve elongation 25,44,51 .
In terms of quality of life and sleep quality, a statistically significant improvement has been found in all followup periods.Other authors have compared radiofrequency diathermy with a simulated control group in subjects with low back pain, finding significant reductions in pain and improvements in trunk muscle activity patterns, which could be related to benefits in performing activities of daily life 42 .Unfortunately, few studies reported on the effects of diathermy on quality of life or sleep quality in patients with low back pain.Masiero et al. 50have linked pain reduction with an impact on quality of life, and other studies that have combined diathermy with exercise have also found improvements in quality of life.However, there is great variability in the conduct of the studies, which does not allow comparison with our results.
Regarding fear of movement, although there are no radiofrequency studies evaluating its effects on the psychological factors of the subject with CLBP, previous studies have shown a strong relationship between the severity and persistence of pain and fear of movement or activity (kinesiophobia) 52 .The results of this study could be explained by the movement avoidance model 53 , where the reduction of pain is related to an improvement in the function and mental state of the subject.There is no doubt that the psychological and biological alterations contribute to the central sensitisation and the development of chronic pain 54 .However, we cannot confirm that the levels of pain affect the results in kinesiophobia.Future studios that relate the fear of movement to disability and other psychosocial variables in patients with chronic low back pain are recommended.
There are several limitations that must be taken into account when considering our data and subsequent interpretation.Firstly, the variables analysed were only monitored in the short and medium term.Due to the chronic nature of the pathology, a long-term evaluation of these variables would have been advisable.Secondly, there is a substantial amount of controversy in determining the most effective treatment parameters, as well as the number of sessions and their duration.It is necessary and very important to compare the effects of this technique with other treatment modalities.Finally, the results have only been verified through clinical and functional evaluations, which are the means available to most physiotherapists and the best method to know the limitations of the patient with musculoskeletal pathology.
As a strength of this research, it should be noted that to our knowledge, this is the first time that PRFcapacitive has been compared with a simulated control group in subjects with CLBP; it is also the first study to measure the effects of MDR on psychological variables such as fear of movement, quality of life, and quality of sleep, factors that could contribute to the individual's recovery process.

Conclusions
In summary, this study found that treatment of CLBP with a 9-session dose of PRF-capacitive produced clinically significant improvements in pain, disability, and functionality (physical outcomes) in the short term, which were also significantly more pronounced than those obtained with simulated treatment.However, the long-term role of PRF-capacitive is unclear and thus further studies are required.*We strongly recommend reading this statement in conjunction with the CONSORT 2010 Explanation and Elaboration for important clarifications on all the items.If relevant, we also recommend reading CONSORT extensions for cluster randomised trials, non-inferiority and equivalence trials, non-pharmacological treatments, herbal interventions, and pragmatic trials.Additional extensions are forthcoming: for those and for up to date references relevant to this checklist, see www.conso rt-state ment.org.

Table 1 .
Patient characteristics at baseline.*Values are expressed as absolute and relative frequencies (n = 60) for categorical variables and as means ± standard deviations for continuous variables.No differences between groups (P > 0.050).

Table 2 .
Baseline, immediate post-treatment, two months follow-up, and change score between groups for disability, pain, kinesiophobia, isometric resistance of abdominal muscles and spinal mobility in flexion.Values are expressed as mean ± standard deviation for baseline, immediate post-treatment and two months follow up and as mean (95% confidence interval) for between-group change scores.*p˂ 0.05 significant ANOVA adjusted from baseline values for differences among group.*MDR, Monopolar Dielectric Radiofrequency; RMD, Roland-Morris Low Back and Disability Questionnaire; ODI, Oswestry Disability Index; VAS, Visual Analogue Scale; TSK, Tampa Scale for Kinesiophobia.Significant values are in bold.

30) Mean Differences and CI between groups over time p Value
During post-treatment, the McQuade test scores increased 15.08 s for patients who received PRF-capacitative treatment and 4.06 s for those receiving simulated therapy.The changes were similar in both groups at the follow-up from the baseline.