Effects of transcutaneous radiofrequency diathermy versus ultrasound on latent myofascial trigger points in the upper trapezius: A randomized crossover trial

Abstract

BACKGROUND:

Currently, the use of radiofrequency diathermy for the treatment of neck pain is booming.

OBJECTIVE:

This study aimed to evaluate the clinical efficacy of Digital Capacitive Diathermy (DCD^®) on stiffness, pain, cervical range of motion, and cervical disability and to compare it with ultrasound (US) in patients with latent myofascial trigger point (MTrP) in the upper trapezius.

METHODS:

Nineteen participants with latent MTrPs in the upper trapezius were included in the assessor-masked, randomized, clinical crossover trial. Subjects were exposed to both interventions: US and DCD^® and treatment effectiveness was measured by myotonometric variables, pressure pain threshold (PPT), visual analog scale (VAS), cervical side-bending flexion ranges, and the neck disability index scale (NDI).

RESULTS:

There were no significant differences between US and DCD^® interventions regarding changes in outcome measures. The US group achieved a statistically significant difference of 2.16 to 1.13 points ( $p=$ 0.005; $r=$ 0.646) for the VAS. The DCD^® intervention showed a statistically significant improvement of 1.11 points for the NDI at 1-week following intervention (95% CI 0.14–2.07; $p=$ 0.27; $d=$ 0.217).

CONCLUSION:

Our findings suggest that DCD^® and US can both be considered effective modalities for the treatment of latent MTrPs, having a longer duration of action with DCD^® therapy.

Keywords

Ultrasound therapy diathermy radiofrequency myofascial trigger point upper trapezius

1. Introduction

A myofascial trigger point (MTrP) is a hyperirritable spot within a palpable taut band (TB) in the skeletal muscle. MTrPs can be clinically classified as active or latent. An active MTrP causes spontaneous local and referred pain, whereas a latent MTrP only causes pain in response to different types of stimulation [1].

MTrPs are a common complaint in patients with musculoskeletal pain with a prevalence of at least 85% in the general population. A high prevalence of MTrPs has been described in patients with neck pain [2]; the upper trapezius is the most common muscle that exhibits MTrPs in the neck area due to its permanent activity and micro-trauma [3]. Although most studies on upper trapezius MTrPs focus on active MTrPs, latent MTrPs are common in this muscle Their identification and treatment are relevant because they can develop into active MTrPs. In addition, both active and latent MTrPs can contribute to neck pain symptoms [4].

Therapeutic ultrasound (US) is a non-invasive technique used by physiotherapists in the pain management. Acoustic waves passing through the tissues increase molecular movement, raising the temperature at depth. These mechanical and thermal effects are responsible for improving tissue extensibility and blood flow, decreasing pain, and increasing metabolism and cell membrane activity [5, 6]. For this reason, it is considered an alternative and safe intervention to minimally invasive techniques [7]. A systematic review found that US treatment was more effective than sham treatment for neck pain and disability due to active or latent MTrPs [8]. However, other studies report little evidence for US therapy’s effectiveness in the treatment of MTrPs, showing that it reduces pain and functionality in the short term still its long-term relevance for clinical practice is unclear [9, 10].

On the other hand, transcutaneous radiofrequency diathermy (TRFD) consists of the emission of high-frequency electromagnetic waves. It is also a non-invasive technique that causes an increase in temperature in-depth within the tissue, which can lead to pain relief and a reduction in inflammation by improving blood flow or oxygen uptake and accelerating cellular activities and metabolism [11, 12, 13]. TRFD has become a popular treatment method in clinical practice due to its low cost, low patient discomfort, and minimal side effects [11]. One of the systems of this technique is the Digital Capacitive Diathermy (DCD^®), a modality that uses the digital treatment of the electromagnetic signal in a monopolar mode with the advantage of reaching deep tissues directly [14, 15].

Although both therapies can generate a thermal effect, the literature shows that the DCD^® produces thermal effects deeper in the tissue and over larger areas than US therapy [16, 17]. However to our knowledge no studies show the effect of this therapy on muscle stiffness and its role in the deactivation of MTrPs. Therefore, this study aimed to investigate the clinical effectiveness of DCD^® on muscle stiffness, pain, cervical range of motion (CROM), and cervical disability and to compare it with US treatment in people with latent MTrPs in the upper trapezius.

2. Methods

2.1 Study design

This study was an assessor-masked, randomized, crossover clinical trial conducted at the Universidad San Jorge (Spain) from February to October 2017, in which participants acted as their own control. The study was approved by the Ethics Committee of Aragon (PI16/030) and followed the clinical practice principles of the Declaration of Helsinki. All participants signed an informed consent form before their participation. This trial was registered on ClinicalTrials.gov Protocol Registration System (reference: NCT03154632) following the CONSORT (Consolidated Standards of Reporting Trials) guidelines.

2.2 Participants

We used a convenience sample and recruited participants by advertising the study among students and staff members of the university where the study was conducted. Volunteers were included if they were 18 years of age or older and presented a latent proximal MTrP (intermediate part of the anterior margin of the upper part of the muscle near the vertical fibers of the muscle attached to the clavicle) in the upper trapezius following the essential criteria proposed by Simons [1, 18]: (1) the presence of a tender spot in a TB or nodules of skeletal muscle; (2) focal spot muscle tenderness; and (3) a pressure-elicited referred pain pattern. The following exclusion criteria were applied: (1) any history of neurological disorders such as radiculopathy; (2) cervical surgery; (3) chronic pain in any part of the body as a result of a traumatic incident; (4) chronic rheumatic disease; (5) medical diagnosis of fibromyalgia; (6) systemic diseases; (7) actual pregnancy; (8) clinical depression; (9) body mass index $\geqslant$ 30; (10) treatment of myofascial syndrome in the muscles of the cervicodorsal area (e.g., physical therapy, invasive techniques, etc.) during the month before the beginning of the study; and (11) ingestion of medication (analgesics, muscle relaxants, psychotropic or anti-inflammatory agents) within three days before the start of the study.

The sample size was calculated to detect a between-group difference of 69 Nm on the stiffness parameter, assuming an SD of 60.8 N/m [19]. The desired statistical power was established at 0.8 and an alpha level of 0.05. A minimum of 19 participants was calculated, including 30% to cover possible losses.

2.3 Randomization and blinding

An external researcher used a web page (www.randomizer.org) to allocate participants to the two interventions sequentially. Random assignment was put in numbered, sealed, and opaque envelopes. The assessor was blinded to sequence intervention allocation.

2.4 Procedure

As per the crossover design, each subject was exposed to 1 session both therapeutic interventions: US and DCD^®. There were two sequences: the sequence of Group 1 was US followed by DCD^®, and the sequence of Group 2 was DCD^® followed by US. A washout period of 1 week was adopted to minimize carryover between interventions.

Each participant was placed in a prone position on a stretcher with arms by their side, their neck in a neutral position with their face in the facial hole, with a cushion under their feet to avoid hyperextension of the knees, and with the area to be treated uncovered. Throughout the procedure, participants were requested to relax completely.

An experienced physiotherapist performed manual palpation to identify the proximal MTrP in the upper trapezius muscles and determine whether a latent MTrP was present according to Simon’s criteria (1) and then marked the identified area on the skin.

2.5 Interventions

2.5.1 US

US (Enraf-Nonius Sonopuls 692, TheNetherlands) was applied to the MTrP area for 6 minutes using a transducer of 5 cm diameter, a frequency of 1 MHz, a duty cycle of 100% (continuous mode), a power density of 1 W/cm², an energy density per treatment of 360 J/cm² and a total energy per treatment of 1800 J. During the application, a gel provided conductivity between the US probe and the skin. The physiotherapist applied a slow circular motion technique with a speed of approximately 2.5 to 4 cm/s over the MTrP area of the upper section of the affected trapezius muscle.

2.5.2 TRFD

The emission of DCD^® was digitally modulated at 140 kHz with a carrier wave of 840 kHz and at 30 V using the ABD Modular Device^® (Biotronic Advance Develops^®, Grenade, Spain). The 6-minute FAST Musculotendinous Injury treatment program with 3 phases was applied to the MTrP area of the upper section of the affected trapezius muscle with a speed of approximately 2.5 to 4 cm/s. The mean power, controlled in %, is increased in each of the phases. Almond oil was used as the dielectric substance to facilitate gliding over the treatment zone.

2.6 Outcome measures

Demographic data, including age, sex, and medical history, were recorded at the beginning of the data collection session.

Myotonometric variables (oscillation frequency, stiffness, and elasticity), pressure pain threshold (PPT), visual analog scale (VAS), and cervical side-bending ranges (contralateral and homolateral) were assessed before intervention (pre-intervention), after intervention (post-intervention) and 1-week after each intervention (follow-up). The neck disability index (NDI) scale was completed by participants before each intervention session (pre-intervention and follow-up). After a week of washing, the same evaluations (pre-intervention, post-intervention, follow-up) will be carried out again but related to the other intervention.

2.6.1 Myotonometry

The Myoton^® PRO (Müomeetria AS, Tallinn, Estonia) was used to measure passive mechanical properties. The device provides a controlled pre-load of 0.18 N for initial tissue compression and then releases an additional 15-ms impulse of 0.40 N of mechanical force, which induces a damped natural oscillation of the tissue. The measured parameters were as follows: 1) oscillation frequency (Hz) as an indicator of muscle tone, which characterizes the resting level of tension in the tissue; 2) logarithmic decrement (arbitrary unit), which is considered as the ability of the muscle to restore its initial shape after being deformed (inversely proportional to elasticity); and 3) stiffness (N/m), which reflects the resistance of the tissue to the force deforming the muscle [20].

A measurement set of ten consecutive impulses (multi-scan mode) with a 1-s interval was completed at each marked point. The mean data of each series were accepted if the coefficient of variation of the measurement set was inferior to 3% [21]. Measurements were perfomed at the proximal MTrP of the affected upper trapezius.

The minimal detectable change in latent MTrPs was from 0.97–1.74 Hz for frequency, 0.48–0.68 for decrement, and 33.12–36.07 N/m-1 for stiffness [21].

The stiffness parameter was considered the primary variable.

2.6.2 PPT

A digital pressure algometer (FPX25, Wagner Instruments, Greenwich, CT) with a 1 cm² probe covered by a latex sheath was used to record the PPT.

The probe was placed on the selected point perpendicular to the muscle plane, and the pressure on the point to be assessed was progressively increased and recorded in N. When the patient reported a change in the sensation of pressure to be painful, the value indicated by the algometer was recorded. It was measured three consecutive times, with an interval of 30 s between each measurement. The highest measurement was discarded, and the other two values obtained for each point were averaged. The subject received no feedback on the values obtained [18, 22].

Measurements were taken at the proximal MTrP in the affected upper trapezius.

The minimum detectable change required for the PPT result to be clinically meaningful in subjects with neck pain was 1.13 kg/cm² [23].

2.6.3 VAS

Participants indicated their current pain intensity using a VAS consisting of a straight 100-mm line with pain descriptors marked “no pain” on the left side and “the worst imaginable pain” on the right side [24]. A minimal detectable change of 15 mm was required for subjects with nonspecific neck pain [25].

2.6.4 CROM

A portable inclinometer (microFET3, Hoggan, USA) was used to assess the active contralateral side-bending range of the cervical spine to evaluate the extensibility of the treated trapezius muscle and the homolateral side-bending range of the cervical spine to evaluate its weakness [18, 22].

During the assessment, participants were seated in a relaxed and comfortable position leaning against the backrest, with their arms resting in their lap. They were asked to focus their visual attention on a marker at placed at a distance of 2 meters to ensure consistent neck positioning throughout the assessment. Subsequently, participants were prompted to perform neck bending movements on the contralateral (contralateral cervical side-bending) and homolateral (homolateral cervical side-bending) sides of the affected trapezius muscle. Three consecutive measurements were taken on each side, with an interval of 30 s between each measurement. A minimal detectable change of 10^∘ was required for the result of CROM in subjects with neck pain [26].

2.6.5 NDI

The validated Spanish version of the NDI was used to assess the degree of disability [27]. The NDI is a self-reporting tool for measuring the condition-specific functional status of subjects with neck pain. The NDI comprises 10 questions related to daily functional activities, including pain, personal care, lifting, reading, headaches, concentration, work, driving, sleeping, and recreation [3, 24]. Each section is scored on a 0-to-5 rating scale, in which 0 means “no pain” and 5 means “worst imaginable pain.” All the points are summed to a total score. The questionnaire can be interpreted as a raw score, with a maximum score of 50 points. A score between 5 and 14 represents a mild disability, between 15 and 24 is interpreted as a moderate disability, between 25 and 34 points as severe, and $>$ 35 reflects a complete disability. A 10-point change is required for the result to be clinically meaningful [24].

2.7 Analisis of data

Data were analyzed with the Statistical Package for the Social Sciences (SPSS) version 28 (SPSS Inc., Chicago, IL, USA). The normal distribution of quantitative variables was assessed using the Shapiro–Wilk test. Demographic data and baseline measurements were compared between the two interventions using the independent Student’s $t$ -test or the Mann-Whitney U test.

Between- and within-intervention analyses were performed using an analysis of variance (ANOVA) mixed model for repeated measures with Bonferroni post hoc pairwise comparisons or Student’s $t$ -test when normal distribution was detected. Non-parametric analysis was performed when non-normal distribution was assumed, using the Mann-Whitney U test for between-intervention comparisons and the Friedman test with the Tukey test to highlight the within-intervention differences. Statistical analysis was conducted at a 95% confidence level, and statistical significance was set at $p<$ 0.05.

Depending on parametric or non-parametric data (Cohen’s $d$ or $r)$ , between- and within-intervention effect sizes were calculated. Negligible, small, medium, and large differences were reflected by effect sizes of $<$ 0.2, 0.2–0.5, 0.5–0.8, and $>$ 0.8, respectively [28].

Table 1
Demographic characteristics of participants

Characteristic	Values
Gender, $n$ (%)
Female	15 (79)
Male	4 (21)
Age, $y$	26.6 $\pm$ 7.9
Height, cm	166.1 $\pm$ 7.9
Weight, kg	64.2 $\pm$ 12.2
Job-status, $n$ (%)
Student	12 (63)
Employee	7 (37)

Abbreviations: y $=$ years, cm $=$ centimeters, kg $=$ kilograms. Values are number and proportion or mean $\pm$ SD.

Figure 1.

Flow diagram.

3. Results

Of the 24 participants recruited for the study, 3 were excluded; hence a total of 21 participants were included. However, due to 2 withdrawals, the final analysis comprised 19 participants. The overall sample was 26.6 $\pm$ 7.9 years of age, predominantly female (78.9%), and 53% exhibited latent proximal MTrPs in the left upper trapezius muscle. Demographic characteristics of the participants are outlined in Table 1. There were no significant differences in outcomes between the two sequence groups at baseline. The flow diagram is shown in Fig. 1.

Table 2
Within- and between-interventions comparison of myotonometric outcomes

Descriptive data					Within-groups effect						Between-group effect
Variable	Inter-	Pre	Post	Follow-up	Post vs pre		Follow-up vs pre		Follow-up vs post		Post		Follow-up
	vention	(mean $\pm$ SD)	(mean $\pm$ SD)	(mean $\pm$ SD)	Mean	Effect	Mean	Effect	Mean	Effect	Mean	Effect	Mean	Effect
					difference	size	difference	size	difference	size	difference	size	difference	size
					(95% CI)		(95% CI)		(95% CI)		(95% CI)		(95% CI)
Oscillation Frequency	US	17.24 $\pm$ 1.71	17.33 $\pm$ 1.80	17.53 $\pm$ 1.41	0.09^† ( $-$ 0.40 to 0.58)	0.050^d	0.29^† ( $-$ 0.49 to 1.08)	0.290^d	0.20^† ( $-$ 0.50 to 0.91)	0.142^d	0.04^† ( $-$ 1.04 to 1.11)	0.037^d	0.09^† ( $-$ 0.94 to 1.12)	0.090^d
[Hz]	RF	17.48 $\pm$ 1.46	17.29 $\pm$ 1.46	17.44 $\pm$ 1.70	0.19^†( $-$ 0.68 to 0.30)	$-$ 0.130^d	$-$ 0.04( $-$ 0.83 to 0.75)	$-$ 0.024^d	0.15 ( $-$ 0.86 to 0.56)	0.088^d
Stiffness [N/m]	US	316.68 $\pm$ 55.90	323.74 $\pm$ 61.23	322.26 $\pm$ 45.41	7.05^†( $-$ 8.77 to 22.87)	0.115^d	5.58^† ( $-$ 17.13 to 28.29)	0.123^d	$-$ 1.48^†( $-$ 23.65 to 20.70)	$-$ 0.033^d	5.69^† ( $-$ 30.96 to 42.33)	0.090^d	3.84^†( $-$ 28.21 to 35.90)	0.078^d
	RF	326.38 $\pm$ 44.51	318.05 $\pm$ 49.53	318.42 $\pm$ 51.81	$-$ 8.33^† ( $-$ 24.14 to 7.51)	$-$ 0.168^d	$-$ 7.96( $-$ 30.65 to 14.76)	$-$ 0.154^d	0.37( $-$ 21.80 to 22.54)	0.007^d
Decrement [a.u.]	US	1.08 $\pm$ 0.23	1.06 $\pm$ 0.21	1.05 $\pm$ 0.21	$-$ 0.02^§ ( $-$ 0.08 to 0.03)	$-$ 0.129^r	$-$ 0.03^§ ( $-$ 0.10 to 0.05)	$-$ 0.134^r	$-$ 0.01^§ ( $-$ 0.07 to 0.06)	$-$ 0.145^r	0.02^‡ ( $-$ 0.12 to 0.16)	0.073^r	$-$ 0.02^‡ ( $-$ 0.16 to 0.12)	$-$ 0.033^r
	RF	1.08 $\pm$ 0.18	1.04 $\pm$ 0.20	1.07 $\pm$ 0.21	$-$ 0.04^§( $-$ 0.08 to 0.01)	$-$ 0.416^r	$-$ 0.01^§( $-$ 0.06 to 0.04)	$-$ 0.025^r	0.03^§( $-$ 0.01 to 0.07)	0.374^r

Abbreviations: Pre, pre-intervention; Post, post-intervention; US, ultrasound; RF, radiofrequency diathermy; SD, standard deviation; CI, confidence interval. ^†Using mixed-design ANOVA; ^‡Using Mann-Whitney U test; ^§Using Friedman test; ^dEffect size expressed as Cohen’s $d$ ; ^rEffect size expressed as $r$ .

Table 3

Within- and between-interventions comparison of PPT, VAS and ROM outcomes

Descriptive data					Within-groups effect						Between-group effect
Variable	Inter-	Pre	Post	Follow-up	Post vs pre		Follow-up vs pre		Follow-up vs post		Post		Follow-up
	vention	(mean $\pm$ SD)	(mean $\pm$ SD)	(mean $\pm$ SD)	Mean	Effect	Mean	Effect	Mean	Effect	Mean	Effect	Mean	Effect
					difference	size	difference	size	difference	size	difference	size	difference	size
					(95% CI)		(95% CI)		(95% CI)		(95% CI)		(95% CI)
PPT [Kg/cm²]	US	16.07 $\pm$ 6.67	16.18 $\pm$ 6.84	16.64 $\pm$ 6.81	0.11^† ( $-$ 2.23 to 2.45)	0.016^d	0.57^† ( $-$ 2.13 to 3.28)	0.084^d	0.47^† ( $-$ 1.56 to 2.50)	0.068^d	0.59^† ( $-$ 3.85 to 5.01)	0.088^d	$-$ 0.65^† ( $-$ 5.05 to 3.76)	0.097^d
	RF	16.64 $\pm$ 6.44	15.59 $\pm$ 6.62	17.29 $\pm$ 6.56	$-$ 1.05^† ( $-$ 3.38 to 1.29)	$-$ 0.159^d	$-$ 0.65^† ( $-$ 2.05 to 3.35)	$-$ 0.099^d	1.70^† ( $-$ 0.34 to 3.73)	0.259^d
VAS [cm]	US	2.16 $\pm$ 1.74	1.13 $\pm$ 1.52	2.90 $\pm$ 2.00	$-$ 1.03^§( $-$ 1.83 to $-$ 0.23)	$-$ 0.646^r	0.74^§ ( $-$ 0.05 to 1.52)	0.482^r	1.77^§ (0.73 to 2.80)^*	0.760^r	$-$ 0.76^‡ ( $-$ 1.92 to 0.40)	0.210^r	0.53^‡( $-$ 0.80 to 1.86)	0.134^r
	RF	2.55 $\pm$ 1.95	1.89 $\pm$ 1.98	2.37 $\pm$ 2.03	$-$ 0.66^§ ( $-$ 1.46 to 0.14)	$-$ 0.484^r	$-$ 0.18^§ ( $-$ 0.97 to 0.60)	$-$ 0.203^r	0.47^§( $-$ 0.56 to 1.51)	0.195^r
Contralateral cervical	US	42.96 $\pm$ 9.64	42.64 $\pm$ 9.58	41.25 $\pm$ 8.81	$-$ 0.32^†( $-$ 2.15 to 1.52)	$-$ 0.033^d	$-$ 1.72^† ( $-$ 4.42 to 0.99)	$-$ 0.194^d	$-$ 1.40^† ( $-$ 3.90 to 1.10)	$-$ 0.158^d	$-$ 1.30^†( $-$ 7.48 to 4.87)	$-$ 0.139^d	$-$ 0.98^†( $-$ 6.81 to 4.84)	$-$ 0.111^d
sidebending [^∘]	RF	43.97 $\pm$ 8.83	43.95 $\pm$ 9.18	42.23 $\pm$ 8.89	$-$ 0.02^† ( $-$ 1.86 to 1.82)	$-$ 0.002^d	$-$ 1.74^† ( $-$ 4.44 to 0.96)	0.196^d	$-$ 1.72^†( $-$ 4.23 to 0.78)	$-$ 0.193^d
Homolateral cervical	US	39.61 $\pm$ 8.05	40.80 $\pm$ 6.65	39.55 $\pm$ 6.81	1.19^†( $-$ 1.62 to 4.00)	0.186^d	$-$ 0.06^† ( $-$ 3.25 to 3.13)	$-$ 0.009^d	$-$ 1.25^† ( $-$ 4.88 to 2.39)	$-$ 0.184^d	$-$ 1.71^†( $-$ 6.57 to 3.15)	$-$ 0.232^d	$-$ 2.20^†( $-$ 2.06 to 6.45)	$-$ 0.340^d
sidebending [^∘]	RF	42.21 $\pm$ 7.72	42.51 $\pm$ 8.05	41.75 $\pm$ 6.12	$-$ 0.30^† ( $-$ 2.51 to 3.11)	$-$ 0.037^d	$-$ 0.47^†( $-$ 3.66 to 2.72)	0.060^d	$-$ 0.76^† ( $-$ 4.40 to 2.87)	$-$ 0.094^d
NDI	US	7.42 $\pm$ 4.89	$-$	7.32 $\pm$ 4.82	$-$	$-$	$-$ 0.10^# ( $-$ 1.70 to 1.49)	$-$ 0.021^d	$-$	$-$	$-$	$-$	$-$ 0.48^¥ ( $-$ 2.79 to 3.74)	$-$ 0.096^d
	RF	7.95 $\pm$ 4.52		6.84 $\pm$ 5.09			$-$ 1.11^# ( $-$ 2.07 to $-$ 0.14)^*	$-$ 0.217^d

Abbreviations: Pre, pre-intervention; Post, post-intervention; US, ultrasound; RF, radiofrequency diathermy; PPT, pain pressure threshold; VAS, visual analog scale; NDI, neck disability index; SD, standard deviation; CI, confidence interval. Statistically significant differences and relevant effect sizes are in bold. ^†Using mixed-design ANOVA; ^‡Using Mann-Whitney U test; ^¥Using Independent Student $t$ -test; ^§Using Friedman test; ^#Using Paired Student $t$ -test; ^dEffect size expressed as Cohen’s $d$ ; ^rEffect size expressed as $r$ ; ^∗ p < 0.05.

The results showed no significant differences between the US and DCD^® interventions regarding changes in outcome measures ( $p>$ 0.05), as seen in Tables 2 and 3.

In the within-group analysis (Tables 2 and 3), the US group achieved a statistically significant difference of 2.16 to 1.13 points ( $p=$ 0.005; $r=$ 0.646) for the VAS, reaching almost 1.5 points of minimal detectable clinical difference, although the analgesic effect of the US disappeared after 1 week. No other significant changes were detected in the other variables for US intervention. In contrast, the DCD^® intervention showed a statistically significant improvement of 1.11 points for the NDI at 1 week following intervention (95% CI 0.14–2.07; $p=$ 0.27; $d=$ 0.217). There were no other significant differences for any variable immediately post or 1-week following DCD^® intervention.

4. Discussion

This study aimed to compare the effectiveness of therapeutic DCD^® compared to US in the management of MTrPs in the upper trapezius muscle. To the best of the authors’ knowledge, no studies have been performed to compare the efficacy of these different electrophysical therapies and this is the first time that DCD^® administration and therapeutic US intervention have been studied as treatments for latent MTrPs in the upper trapezius muscle. At the end of this study, no significant differences were found in any of the studied variables (myotonometry, PPT, VAS, lateral flexion, and NDI) when comparing the two interventions. However, differences were found in the within-intervention analysis. A decrease in pain was noted in both interventions, and this decrease was significant with the US technique immediately after application. At the one-week measurement, it was found that participants treated with DCD^® showed a reduction in the NDI, in contrast to the US technique.

These results are consistent with the study by Lee et al., which compared the use of these two techniques in chronic lower back pain and obtained very similar results. In subjects treated with US and TRFD, there was a significant decrease in pain immediately following the application, and no significant differences were found between the groups. On the other hand, long-term therapeutic effects were significantly maintained in subjects treated with TRFD for up to 12 weeks after treatment [29]. Some studies have provided evidence of the therapeutic use of US for short-term pain relief [30, 31, 32]. Diego et al. obtained similar results in terms of pain reduction when they compared the TRFD treatment with a control group for the treatment of neck pain [33]. Moreover, Sarrafzadeh et al. also found a pain reduction in the latent upper trapezius after six US sessions, with parameters similar to ours [34].

In our study, both techniques showed no significant improvement in myotonometry, PPT, and CROM. Considering the effect of DCD^® and US on muscle stiffness, no studies have investigated the influence of these techniques on the change in muscle stiffness of MTrPs. However, other myofascial therapies assessed changes in muscle stiffness measured by myotonometry. Kisilewicz et al. found a reduction in the stiffness parameter of an active upper trapezius MTrP in elite basketball players after a unique session of local ischemic compression [35]. Likewise, one session of dry needling targeting the latent medial MTrP of the right soleus muscle modified the stiffness outcome [36]. According to Kavadar et al., a single session of continuous US was more effective than placebo US for increasing the PPT of active MTrPs on the upper trapezius [37]. Moreover, in a recent case series study in women with endometriosis, the number of MTrPs decreased in all participants and with higher PPTs after an intracavitary application of DCD^® intervention [38]. With regards to CROM, some studies have shown an increase in neck range of motion after the application of US [33]. In addition, some authors have studied the effects of TRFD devices at CROM [11]. For example, Albornoz-Cabello et al. demonstrated a significant improvement in functionality and range of motion in patients with patellofemoral pain syndrome through the use of DCD^® [39, 40].

The findings, in which DCD^® achieves an improvement in functional status, although not immediately but in the long-term, could be explained by the thermal effect that increases blood circulation in the treatment area, leading to an increase in metabolism and improving changes such as muscle spasm, improving the altered threshold of receptors and promoting a healing process [41, 42]. In contrast, the mechanism of acoustic cavitation in therapeutic US treatment has been shown to inhibit pain by stimulating the nervous system. Nevertheless, it was not able to produce deep thermal effects that lasted over a longer time [9, 34, 43, 44].

Some of the existing limitations of this research should be mentioned. Although the sample size was calculated for a crossover design, the overall sample was small. Only one session was conducted for each technique. Moreover, there was no long-term follow-up. Future studies should be fully randomized and blinded clinical studies including both techniques into the standard treatment to assess their efficacy in the treatment of myofascial syndrome. At the same time, the main strength of this study is that the two techniques were isolated to assess their efficacy, which has not been done before in a single session.

5. Conclusions

Although the application of DCD^® showed pain reduction in the MTrPs of the upper trapezius, it was not as significant as the US technique. However, a significant improvement in functional status with DCD^® was perceived by the participants one week after the intervention. The clinical findings suggest that the use of DCD^® could be considered as a treatment option for latent MTrPs in the upper trapezius. However, further studies on the frequency and duration of DCD^® application, in combination with other myofascial techniques and longer follow-up period, are needed for more conclusive results.

Author contributions

Carolina Jiménez-Sánchez: Conceptualization, Investigation, Methodology, Data curation, Resources, Writing – original draft, Writing – review & editing, Supervision. Paula Cordova-Alegre: Investigation, Methodology, Writing – original draft, Writing – review & editing. Beatriz Carpallo-Porcar: Formal analysis, Data curation, Software. Jose Manuel Burgos-Bragado: Writing – original draft. Daniel Sanjuan-Sánchez: Writing – original draft. Natalia Brandín-de la Cruz: Writing – review & editing, Supervision.

Data availability statement

The data that support the findings of this study are available from the corresponding author on request.

Ethical approval

Ethical approval was obtained from the Ethical Committee of Aragon (CEICA) (number PI16/030).

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Informed consent

Written informed consent was obtained from all participants.

Footnotes

Acknowledgments

We acknowledge the participants of the study.

Conflict of interest

The authors declare no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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Effects of transcutaneous radiofrequency diathermy versus ultrasound on latent myofascial trigger points in the upper trapezius: A randomized crossover trial

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

2. Methods

2.1 Study design

2.2 Participants

2.3 Randomization and blinding

2.4 Procedure

2.5 Interventions

2.5.1 US

2.5.2 TRFD

2.6 Outcome measures

2.6.1 Myotonometry

2.6.2 PPT

2.6.3 VAS

2.6.4 CROM

2.6.5 NDI

2.7 Analisis of data

Table 1 Demographic characteristics of participants

Table 2 Within- and between-interventions comparison of myotonometric outcomes

5. Conclusions

Author contributions

Data availability statement

Ethical approval

Funding

Informed consent

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
Demographic characteristics of participants

Table 2
Within- and between-interventions comparison of myotonometric outcomes