Immediate effects of TENS and HVPS on pain and range of motion in subacromial pain syndrome: A randomized,placebo-controlled,crossover trial

Abstract

BACKGROUND:

Transcutaneous electrical nerve stimulation (TENS) is one of the most common methods for managing shoulder pain, and high voltage pulsed currents (HVPS) may be used for reducing pain. However, their immediate effects on resting pain and pain-free active range of shoulder motion (pfROM) in patients with subacromial pain syndrome (SAPS) have not been studied comparatively, yet.

OBJECTIVES:

The aim of this study was to compare the immediate effects of TENS, HVPS and placebo stimulation on shoulder resting pain and pfROM in patients with SAPS.

METHODS:

Randomized, placebo-controlled, double-blind, crossover study. One hundred and six patients with SAPS received placebo (predetermined 1st day application), TENS and HVPS with 1-day interval, in a random sequence. Before and after each application, resting pain and pfROM were evaluated by 0–10 cm visual analogue scales and a digital inclinometer, respectively.

RESULTS:

Intensity of pain decreased significantly after TENS, HVPS and placebo interventions ( $p<$ 0.05). While pfROMs increased significantly after TENS and HVPS ( $p<$ 0.05), remained unchanged after placebo, except for internal and external rotations ( $p>$ 0.05). The most obvious effects on pain and pfROMs occurred after HVPS ( $p<$ 0.05).

CONCLUSION:

In patients with SAPS, both HVPS and TENS, but preferably HVPS can be used effectively to decrease pain and increase pfROM.

Keywords

Shoulder pain joint range of motion electrotherapy physiotherapy orthopedics transcutaneous electrical nerve stimulation high voltage pulsed currents

1. Background

All non-traumatic, usually unilateral shoulder problems that cause pain, localized around the acromion, often worsening during or subsequent to lifting of the arm are defined as subacromial pain syndrome (SAPS) [1]. Bursitis, tendinosis calcarea, supraspinatus tendinopathy, partial tear of the rotator cuff, biceps tendinitis, or tendon cuff degeneration are different clinical and/or radiological names under this title [1].

SAPS, which is reported to be the most frequent cause of shoulder pain during physician office visits, gradually leads to functional loss and disability, hence, negatively affects quality of life [2, 3]. It is preferably treated by conservative approaches such as rest, nonsteroidal anti-inflammatory drugs, corticosteroid injections, extracorporeal shock wave therapy, exercise therapy, mobilizations, massage, laser therapy, hot-cold agents, acupuncture, bandaging, ultrasound (US) therapy, electrical stimulation, magnetic field therapy and combined methods [1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]. In a systematic review by Haik et al. [13], which investigated physical therapy modalities for SAPS on pain, function/disability or range of motion, it was reported that there was high level of evidence regarding the lack of beneficial effects of physical resources such as low-level laser, US and pulsed electromagnetic field (PEMF) in the treatment of SAPS, and there was limited evidence for microwave diathermy and TENS.

Transcutaneous electrical stimulation (TENS) and high voltage pulsed current/stimulation (HVPS) are both electrophysical agents which can be used for pain relief in musculoskeletal conditions. Standard TENS devices usually deliver biphasic pulsed currents with a pulse duration between 50 $\mu$ s and 1000 $\mu$ s and pulse frequencies between 1 and 250 pps [14, 15]. HVPS devices are TENS-like devices which deliver direct current with twin monophasic spiked pulses of 10–500 V (500-ohm load) with a short pulse duration (microseconds) [14, 15, 16, 17]. In both conventional TENS technique and HVPS for pain relief, the aim is to activate spinal gating mechanism by selectively stimulating large diameter A $\beta$ fibers [14, 15, 16, 17]. In theory, high-frequency (approximately 10–250 pps), low-intensity (nonpainful) currents are most efficient in selectively activating A $\beta$ fibers, which is practically recognized by the user reporting ‘strong but comfortable’ nonpainful electrical paresthesia beneath the electrodes [14, 15].

Approximately 1/3 of physiotherapists use pain-focused electrotherapy within their treatment programs for patients with subacromial impingement syndrome [11]. Johansson et al. investigated clinicians’ beliefs in interventions for subacromial pain and reported that the majority of physiotherapists (68%) has trust in TENS, although there is no available evidence for its efficacy in patients with subacromial pain [8]. The lack of evidence for the efficacy of TENS as well as other pain-focused electrotherapy agents may be due to the use of inadequate research designs and methodological weaknesses of the studies [6]. In addition, there has been little experimental work on the effects of HVPS on pain relief in the literature [14, 15] and no study for its efficacy in SAPS.

According to the Philadelphia Panel regarding rehabilitation interventions for shoulder pain, there is an urgent need for prospective randomized controlled trials, which use rigorous methods such as use of an appropriate placebo and double-blind procedure, adequate randomization, homogeneous sample of patients and adequate sample size [6]. Therefore, the aim of this study is to investigate and compare the immediate effects of single session applications of conventional TENS and HVPS on pain and pain-free range of active shoulder motions (pfROMs) in patients with SAPS, using a placebo-controlled, double-blind, randomized method in crossover design.

2. Methods

2.1 Study design and setting

This study was carried out at a private hospital in Fethiye, Muğla, between November 2015 and January 2017. The study was performed in accordance with the ethical standards in the 1964 Declaration of Helsinki. The Scientific Research Ethical Board of Muğla Sıtkı Koçman University approved this study (Protocol no: 161, Decision no. 145, Date: 22.10.2015). This double-blind, randomized, placebo-controlled crossover trial is registered on ClinicalTrials.gov (NCT03588143).

2.2 Participants

The participants in this study were outpatients of a physical therapy and rehabilitation clinic. They were diagnosed with SAPS (Neer stage 1–2) by a physician according to the Guideline of Dutch Orthopedic Association [1, 18]. Within the study calendar, among 164 patients diagnosed with SAPS, 106 met the inclusion criteria, signed the informed consent, andwere recruited (Fig. 1). The inclusion criteria were: (1) being 18–65 years-old; (2) having pain with active shoulder movements; (3) being diagnosed with SAPS for 1–10 weeks; (4) positive Hawkins-Kennedy and painful arc tests; (5) infraspinatus weakness; and (6) a negative drop-arm test for patients with partial rotator cuff tear [10, 11]. The exclusion criteria were: (1) radiologically confirmed malignity or acromial/acromioclavicular arthritis; (2) history of fracture or surgery in the affected shoulder-arm complex; (3) clinically confirmed polyarthritis, rheumatoid arthritis, fibromyalgia, adhesive capsulitis or osteoarthritis of the glenohumeral joint or subacromial region; (4) cervical or thoracic spinal problems; (5) neurological problems which may affect upper extremity movements or pain perception (stroke, peripheral neuropathy, brachial plexus lesion, etc.); (6) using anti-inflammatory, analgesic, or myorelaxant medicine during the study; (7) body mass index ${\geqslant}$ 28 kg/m ${}^{2}$ ; (8) contraindications for TENS and/or HVPS (damaged skin, impaired sensation, etc.); and (9) previous experience with electrophysical agents or physiotherapy.

Figure 1.

Flow diagram of the study.

Physical (age, gender, height, weight, body mass index values) and sociodemographic (occupation, educational level, marital status) characteristics of the participants, as well as the affected shoulder (right/left) and time since diagnosis of SAPS (week) were recorded.

Outcome measures of this study were intensity of resting pain and pfROMs. The participants were asked to mark their resting pain intensity on a 0–10 cm visual analogue scale, where 0 cm indicated no pain and 10 cm indicated unbearable pain. The distance of the marked point from zero point was recorded as the intensity of pain.

Pain-free ranges of active shoulder flexion, abduction, internal and external rotation were measured by a digital inclinometer (Baseline Digital Inclinometer, 2008 New York-USA), which was calibrated on a flat surface before each measurement. Pain-free active shoulder internal and external rotations were measured in supine-hook lying position, where the shoulder was in 90 ${}^{\circ}$ abduction and elbow in 90 ${}^{\circ}$ flexion. The inclinometer was placed on the medial edge of ulna and on lateral edge of radius, for external and internal rotation measurements, respectively. Pain-free active shoulder flexion and abduction were measured while the subject was sitting straight on a chair with back support, with hips and knees in 90 ${}^{\circ}$ flexion. For both movements, the inclinometer was placed on the midline of the humerus, proximal to the elbow joint [19].

All evaluations were performed before and just after each modality, which were applied in three consecutive days, with 24 hours’ washout period. All of the measurements were performed by a physiotherapist blinded to the modalities applied (placebo/TENS/HVPS).

2.3 Interventions

In this crossover study, closed opaque envelopes including numbers which indicate the interventions, were used for randomizing the order of interventions. However, at the first day, all subjects received placebo intervention in order to prevent them to distinguish the feelings of current and placebo applications. The subjects only knew the number written inside of the closed envelope they chose, and only the physiotherapist who applied the interventions knew the indications of the numbers. Therefore, subject blinding was assured. All pfROM assessments were carried out by another physiotherapist who was kept blind to the interventions applied. No other interventions (medication, physiotherapy, advice, etc) were given to the subjects till the end of three-day trial.

All interventions (placebo, TENS and HVPS) were applied by the same combined electrotherapy device (Intelect Advanced, Model 2762CC, Chattanooga Group-USA) and the electrodes with same characteristics (5 $\times$ 5 cm, Dura-Stick Self-adhesive Electrodes, Chattanooga Group-USA). Four electrodes from two channels were placed as crossing each other and surrounding the affected area, after cleaning the site with alcohol in order to decrease the skin impedance.

The subjects were sitting on an armchair with their elbows flexed at about 90 ${}^{\circ}$ position on armrests during all interventions. In placebo application, the placement of the electrodes was the same with TENS and HVPS applications, however, only the time unit of the electrotherapy device was activated for 30 minutes, without giving any current.

Figure 2.

Comparison of within-intervention differences of visual analogue scale scores (cm) and pfROM values ( ${}^{\circ}$ ). TENS: Transcutaneous electrical nerve stimulation, HVPS: High voltage pulsed currents, SD: Standard deviation, ${}^{*}$ Signifıcant difference ( $p<$ 0.05) (repeated measures analysis of variance-ANOVA).

TENS was applied with asymmetrical biphasic current at 65 $\mu$ s pulse duration and 100 Hz frequency, in continuous pattern [14, 15, 16, 17]. The strongest intensity that remained comfortable without causing pain and any muscle twitch/contraction was adjusted and this sensory level was maintained during 30 minutes of treatment to prevent accommodation. HVPS was applied with twin spiked monophasic current at 100 pps frequency, in continuous pattern, for 30 minutes [16, 17]. The current intensity was adjusted and recorded as described in TENS application.

2.4 Statistical analysis

The sample size was calculated by G-Power statistical software package version 3.1.9.3 for Mac ( $\alpha=$ 5%, power test ${\geqslant}$ 80%, effect size $F=$ 0.25 for repeated measures analysis of variance (ANOVA) for 2 $\times$ 3 $=$ 6 measurements in crossover design), resulting in $n=$ 93. SPSS for MAC 23.0 program was used for statistical analysis. Pain intensity and pfROM were the dependent and the intervention methods (placebo, TENS and HVPS) were the independent variables. Kolmogorov-Smirnov test was used for the analysis of compliance with the normal distribution. According to this test result, dependent variables were compared by paired samples $t$ -test, and independent variables by one-way ANOVA in repeated measures. Statistical significance was set at 95% confidence interval (CI) and $p{<}$ 0.05.

Table 1
Physical and sociodemographic characteristics ( $n=$ 106)

Physical characteristics	Mean $\pm$ SD
Age (year)	50.55	$\pm$ 10.38
Height (cm)	168.21	$\pm$ 8.43
Weight (kg)	75.29	$\pm$ 11.27
Body mass index (kg/m ${}^{2}$ )	26.47	$\pm$ 2.97
Sociodemographic characteristics	$n$ (%)
Education
Literate	3	(2.8)
Primary	50	(47.2)
High school	19	(17.9)
Undergraduate	30	(28.3)
Graduate	4	(3.8)
Occupation
Retired	22	(20.8)
Self-employed	31	(29.2)
White-collar worker	8	(7.5)
Blue-collar worker	12	(11.3)
Farmer	2	(1.9)
Housewife	31	(29.2)
Marital status
Married	92	(86.8)
Single	11	(10.4)
Divorced	3	(2.8)

$n$ : Sample size, SD: Standard Deviation, cm: centimeter, kg: kilogram, m: meter.

Table 2

Visual analogue scale scores (cm) before and after interventions

$n=$ 106	Pre-intervention Mean $\pm$ SD	Post-intervention Mean $\pm$ SD	$t$	$p$ value	95% CI
Placebo	5.94 $\pm$ 1.69	5.74 $\pm$ 1.95	2.55	0.01 ${}^{*}$	0.04 to 0.35
TENS	6.05 $\pm$ 1.79	5.51 $\pm$ 1.85	10.33	0.00 ${}^{*}$	0.43 to 0.63
HVPS	6.11 $\pm$ 1.75	4.81 $\pm$ 1.76	16.11	0.00 ${}^{*}$	1.14 to 1.46

TENS: Transcutaneous electrical nerve stimulation, HVPS: High voltage pulsed currents cm: centimeter, SD: Standard deviation, ${}^{*}$ : Pre and post intervention scores were signifıcantly different ( $p<$ 0.05) (Paired samples $t$ -test).

Table 3

PfROM values ( ${}^{\circ}$ ) before and after interventions

$n=$ 106		Pre-intervention Mean $\pm$ SD		Post-intervention Mean $\pm$ SD		$t$	$p$ value	95% CI
Placebo	Flexion	108.19	$\pm$ 31.24	107.86	$\pm$ 30.87	0.78	0.440	$-$ 0.51 to 1.18
	Abduction	90.18	$\pm$ 31.37	90.43	$\pm$ 31.53	$-$ 0.59	0.554	$-$ 1.11 to 0.60
	External rotation	52.04	$\pm$ 20.94	52.94	$\pm$ 21.31	$-$ 2.56	0.012 ${}^{*}$	$-$ 1.61 to $-$ 0.21
	Internal rotation	42.43	$\pm$ 17.20	43.35	$\pm$ 16.68	$-$ 2.68	0.009 ${}^{*}$	$-$ 1.59 to $-$ 0.24
TENS	Flexion	107.99	$\pm$ 31.13	111.36	$\pm$ 31.58	$-$ 7.79	0.000 ${}^{*}$	$-$ 4.23 to $-$ 2.51
	Abduction	89.97	$\pm$ 31.03	92.41	$\pm$ 30.74	$-$ 6.77	0.000 ${}^{*}$	$-$ 3.15 to $-$ 1.72
	External rotation	52.63	$\pm$ 20.18	54.54	$\pm$ 20.18	$-$ 5.30	0.000 ${}^{*}$	$-$ 2.62 to $-$ 1.19
	Internal rotation	43.15	$\pm$ 16.69	44.81	$\pm$ 16.19	$-$ 4.77	0.000 ${}^{*}$	$-$ 2.35 to $-$ 0.97
HVPS	Flexion	107.96	$\pm$ 30.70	113.11	$\pm$ 31.18	$-$ 12.84	0.000 ${}^{*}$	$-$ 5.95 to $-$ 4.36
	Abduction	90.46	$\pm$ 31.03	94.85	$\pm$ 30.73	$-$ 11.12	0.000 ${}^{*}$	$-$ 5.17 to $-$ 3.60
	External rotation	52.36	$\pm$ 20.58	55.60	$\pm$ 20.04	$-$ 8.21	0.000 ${}^{*}$	$-$ 4.03 to $-$ 2.46
	Internal rotation	42.74	$\pm$ 16.10	45.21	$\pm$ 16.06	$-$ 6.33	0.000 ${}^{*}$	$-$ 3.25 to $-$ 1.70

PfROM: Pain-free active range of shoulder motion, TENS: Transcutaneous electrical nerve stimulation, HVPS: High voltage pulsed currents, SD: Standard deviation, ${}^{*}$ : Pre and post intervention values were statistically different ( $p<$ 0.05) (Paired samples $t$ -test).

3. Results

The study sample consisted of 61 women (57.5%) and 45 men (42.5%) with SAPS, who were 24–65 years-old. Their physical and sociodemographic characteristics are presented in Table 1. In 94 (88.7%) participants, the right extremity was the dominant extremity, and only 65 (61.3%) of them had suffered the injury to that extremity. Mean time since diagnosis was 1.45 $\pm$ 1.16 weeks (minimum $=$ 1 week, maximum $=$ 10 weeks). Measures of key outcomes were obtained from all of the subjects and all subjects received intervention conditions as allocated.

There were no significant baseline differences of pre-intervention values of pain intensity and pfROM ( $p{>}$ 0.05). Pain intensity of the subjects decreased significantly after each intervention (for placebo: $p=$ 0.012, 95% CI $=$ 0.04 to 0.35; for TENS: $p{<}$ 0.001, 95% CI $=$ 0.43 to 0.63; for HVPS: $p{<}$ 0.001, 95% CI $=$ 1.14 to 1.46) (Table 2). The greatest decrease in pain intensity occurred after HVPS (Fig. 2).

All PfROMs significantly improved after TENS ( $p{<}$ 0.001) and HVPS ( $p{<}$ 0.001) interventions (Table 3). After placebo intervention, no significant change was observed in pfROM values, except internal and external rotations ( $p=$ 0.009 and $p=$ 0.012, respectively) (Table 3). TENS and HVPS increased flexion and abduction more than placebo, and the maximum amount of increase in pfROMs occurred after HVPS (Fig. 2).

4. Discussion

Both TENS and HVPS are commonly used methods in orthopedic rehabilitation with the aim of relieving pain. However, the effectiveness of HVPS on SAPS has not been reported previously, and this is the first randomized and placebo-controlled study to compare the effects of TENS and HVPS on pain and pfROM in patients with SAPS.

The findings reveal that both interventions are effective in decreasing rest pain and increasing pfROMs, and HVPS is more effective than TENS and placebo applications on the outcomes.

Both conventional TENS and HVPS have been proposed to promote pain relief through spinal gating mechanism by stimulating the large afferent neurons (A $\beta$ ) selectively [16]. In order to stimulate A $\beta$ neurons selectively, using currents with pulse duration lower than 150 $\mu$ sec and pulse frequency higher than 80 Hz is recommended [20]. Pulse duration and pulse frequency of TENS and HVPS used in this study are similar to each other and accord with these parameters. However, waveform of high voltage pulsed currents and the voltage of the generator differ from TENS [16]. Twin-spiked monophasic waveform of high voltage pulsed current may cause a wider depolarization of axons via temporal summation. The phase duration at the base of each member of a pair is much less as the peak of the spike is approached [16]. The exceptionally brief phase duration of high voltage currents and low average current intensity decrease discomfort of HVPS, while its high peak current allows deeper penetration [21]. In addition to these waveform characteristics, high voltages bypass the impedance of the skin, and because of these properties, HVPS helps to eliminate chemical and thermal reactions due to electrical stimulation [16, 21]. The findings of the present study which indicate that HVPS is more effective than TENS and placebo applications in decreasing SAPS pain may be rationalized through these waveform and voltage characteristics of HVPS. Same explanations apply to the findings about pfROMs, since being directly related with the pain parameter.

Although there were significant differences among the interventions, placebo application also caused a decrease in pain. This finding may indicate that success of TENS and HVPS depends not only on physiological but also their placebo effects. After placebo intervention, only pain free internal and external rotation ranges increased significantly. This may be due to the biomechanical advantage of the measurement positions used for rotations. Supine position with 90 ${}^{\circ}$ shoulder and elbow flexion might have shortened the lever arm and let the gravity help to the motion, so the muscles might have been able to function with less work load. In addition, internal and external rotations were the last measured motions in the measurement sequence. Previous measurements might have caused an increase in joint mobility. Therefore, advantages of both the measurement position and the measurement sequence can be considered as an explanation for similarity of pain free internal and external rotation range changes between placebo and other interventions.

Literature findings related with TENS in shoulder pain generally report its cumulative effects at the end of several sessions, and in comparison with other electrophysical agents such as US, interferential therapy and radiofrequency currents, as well as with placebo intervention [22, 23, 24, 25, 26]. However, there is lack of knowledge about the immediate effects of TENS on shoulder pain, and to our knowledge, the only relevant research is the study of Başkurt et al. [27]. In that study, the authors have found that TENS (100 Hz frequency, 0.1 ms pulse duration, symmetrical biphasic waveform, tolerable intensity) was effective in decreasing pain in stage I shoulder impingement syndrome. This finding supports the results of the present study, which indicate that the immediate effect of TENS on reduction of pain in patients with SAPS was significant.

Lack of randomization in the sequence of pfROM measurements stands as a limitation for this study. In addition, only immediate effects of interventions have been investigated, and no conclusions at the moment can be drawn about their cumulative or long-term effects. In addition, only time since SAPS diagnosis was recorded, but information about the duration of SAPS symptoms in this sample is lacking. Therefore, it is difficult to identify if the study sample had an acute or chronic condition. This point may be a limitation for generalizability of the findings.

5. Conclusion

The main strength of this study stands on its rigorous methodology including use of an appropriate placebo and double-blind procedure, adequate randomization, homogeneous sample of patients and adequate sample size. Since the guideline for diagnosis and treatment of SAPS recommends movement and exercises which specifically focus on rotator cuff and scapular stabilizers within the pain threshold [1], inclusion of TENS or preferably HVPS within treatment sessions prior to these exercises, may contribute to desirable outcomes.

Footnotes

Acknowledgments

This research (Project Grant Number 16/044, title “Acute Effects of Transcutaneous Electrical Nerve Stimulation and High Voltage Pulsed Stimulation on Subacromial Pain and Shoulder Movements”) was supported by the Muğla Sıtkı Koçman University Research Projects Coordination Office. The authors thank Levent Eker (MD) for helping to determine the sample size; Erhan Çetin (MD) for referring eligible patients to the study; Sera Kopuz (PT) for her valuable help in evaluating the patients, and the Private Lokman Hekim Hospital staff for their support in arranging the workplace conditions.

Conflict of interest

Each author certifies that he or she has no commercial associations (e.g., consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article.

Funding

This paper is a part of the thesis by Furkan Bilek, which has been granted by the Muğla Sıtkı Koçman University Research Projects Coordination Office (Project Grant Number: 16/044, title “Acute Effects of Transcutaneous Electrical Nerve Stimulation and High Voltage Pulsed Stimulation on Subacromial Pain and Shoulder Movements”).

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