Effect of Interferential Current Stimulation in Management of Hemiplegic Shoulder Pain
,
,
Akkradate Siriphorn, PhD
,
Department of Physical Therapy, Faculty of Allied Health Sciences, Chulalongkorn University, Bangkok, Thailand
Published Online: April 21, 2014
Abstract
Objective
To study the immediate effects of interferential current stimulation (IFC) on shoulder pain and pain-free passive range of motion (PROM) of the shoulder in people with hemiplegic shoulder pain (HSP).
Design
Double-blind, placebo-controlled clinical trial.
Setting
Institutional physical therapy clinic, neurologic rehabilitation center.
Participants
A population-based sample of people with HSP (N=30) was recruited.
Intervention
Participants were divided into 2 groups—an IFC group and a placebo group—by using a match-paired method (age, sex, and Brunnstrom motor recovery stage). In the IFC group, participants received IFC for 20 minutes with an amplitude-modulated frequency at 100Hz in vector mode. The current intensity was increased until the participants felt a strong tingling sensation.
Main Outcome Measures
Pain intensity and pain-free PROM of the shoulder until the onset of pain were measured at baseline and immediately after treatment.
Results
Participants reported a greater reduction in pain during the most painful movement after treatment with IFC than with placebo (P<.05). The IFC group showed a greater improvement in posttreatment pain-free PROM than the placebo group in shoulder flexion (P<.01), abduction (P<.01), internal rotation (P<.01), and external rotation (P<.01).
Conclusions
This study provides evidence that IFC is effective for the relief of pain during movement and also increases the pain-free PROM of the shoulder in people with HSP.
List of abbreviations:
HSP (hemiplegic shoulder pain), IFC (interferential current stimulation), NRS (numeric rating scale), PROM (passive range of motion)
Hemiplegic shoulder pain (HSP) is one of the most important complications of stroke.1 The incidence of HSP in the past decade was approximately 17% to 37% in people with acute stroke, and it increased to 47% in people with chronic stroke.2, 3, 4, 5, 6 The pain experienced by people with HSP can limit efforts to restore or maintain the shoulder's range of motion.1 This reduced range of motion decreases the patients' quality of life,7 delays poststroke recovery, and may increase their length of stay in the hospital.8 Therefore, the prevention of further complications after the onset of HSP should be addressed, especially the reduction of shoulder pain to maintain or improve the shoulder's range of motion in people with HSP.
The possible causes of HSP are rotator cuff tears, rotator cuff and deltoid tendinopathy,9, 10 and bicipital and supraspinatus tendon tenderness.4 The pathology of these causes involves the deep tissues more than the superficial tissues of the shoulder. Thus, pain management of HSP should consider the onset of HSP as well as the pathologic aspects to yield the most effective results in preventing post-HSP complications.
Interferential current stimulation (IFC) is one of the physical therapy modalities used for relieving pain caused by deep tissue injury. IFC is the transcutaneous application of alternating, medium-frequency electrical current for therapeutic purposes.11 IFC has been reported to relieve pain related to shoulder12 and knee13 conditions and in experimental modeling.14 However, there is a lack of evidence on the effect of IFC in people with HSP. Therefore, the aim of this study was to investigate the immediate effects of IFC on shoulder pain and pain-free passive range of motion (PROM) of the shoulder in people with HSP.
Methods
Research design
A double-blind, placebo-controlled clinical trial was carried out to investigate the effects of IFC on shoulder pain and pain-free PROM of the shoulder. This study was conducted at an institutional physical therapy clinic and a neurologic rehabilitation center in Thailand. Participants gave informed consent after the purpose and testing procedures of this study were explained. The study protocols were approved by the Ethic Review Committee for Research Involving Human Projects (Chulalongkorn University and Prasat Neurological Institute in Thailand).
Participants
Thirty participants with a diagnosed first stroke (ischemic or hemorrhagic) were recruited to the study. All participants met the following criteria: (1) were >20 years of age; (2) had pain ≥3 on an 11-point numeric rating scale (NRS) in the affected shoulder within 3 months of stroke onset; (3) had adequate communication abilities (to communicate their pain through an NRS in Thai); (4) had normal light touch and pin-prick sensation on the affected shoulder; (5) had a Brunnstrom motor recovery stage rating of 1 to 315; (6) had no cognitive impairment (detected by Mini-Mental Status Exam–Thai 2002)16; (7) had no history of arrhythmias; (8) had no unresolved pathology and ongoing symptoms in the affected shoulder before the onset of stroke; (9) had no history of cancer or tumors; (10) had no implanted cardiac pacemaker; (11) had no skin problems, wounds, or infections on the affected shoulder; (12) had no metal, such as surgical surface staples, external pins, or internal fixations, in the affected shoulder; (13) had no history of botulinum toxin or steroid injections, subscapular nerve block, or surgery at the shoulder joint; (14) had never used electrical stimulation therapy; and (15) had no history of analgesic medication use in the past 12 hours. Participants were excluded if they could not complete the session.
Outcome measures
Pain intensity
Shoulder pain was assessed by an 11-point NRS.17 This tool was simple to use and had high correlation coefficients (.94–.96) with the visual analog scale, verbal rating scale, and Faces Pain Scale–Revised. The pain intensity was graded from 0 (no pain) to 10 (the most intense level of pain). The participants were asked to report their pain level at rest and during movement. The most painful movement score was used for further data analysis.
Pain-free PROM of the shoulder
Pain-free PROM of the shoulder was designated as the range of motion attained at the “point of the first onset of pain” and was measured with a digital goniometera in 6 directions. Five directions of the shoulder joint were measured (flexion, abduction, adduction, internal rotation, external rotation) while participants were lying in a supine position. Additionally, shoulder extension was measured in the side-lying position. Before the present study, the test-retest reliability of the digital goniometer measurement was conducted in 16 healthy participants. The intrarater reliability in all movement directions of the shoulder joint ranged from good to high (intraclass correlation coefficients, .73–.97). The SE for the measurements and the minimal detectable change of the measurements for all PROM measurements of the shoulder were within 2° and 4.5°, respectively.
Procedure
At the beginning of treatment, the first investigator recorded the demographic data and clinical characteristics of the participants. The demographic data consisted of age, sex, hemiplegic side, etiology (ischemic or hemorrhagic stroke), stroke duration (time from stroke onset to time participants entered the program), and pain duration (time from pain onset to time participants entered the program). The clinical characteristics included upper extremity motor recovery assessment by Brunnstrom stages,15 shoulder muscle tone assessed by the Modified Ashworth Scale,18 shoulder subluxation assessed by measuring the subacromial space with the finger breadth unit,19 and upper limb functions measured with item 6 (upper limb function) of the Motor Assessment Scale for stroke.20
The participants were then divided into 2 groups—an IFC group and a placebo group—by using the match-paired method (age, sex, and Brunnstrom motor recovery stage). This procedure was performed by the second investigator, who was not involved in any data collection. After that, participants in both groups were assessed by the first investigator to obtain the pretreatment data. The pretreatment data included the NRS scores of shoulder pain at rest and during the most painful movement, and the pain-free PROM of the shoulder in all directions. Once the examination was complete, all participants were helped to a sitting position with elbow support. The skin overlying the affected shoulder was cleaned with alcohol. Four single-use electrodesb (56×56mm) were placed around the painful area of the shoulder using the crisscross technique to deliver a quadripolar interferential current.21 The third investigator, a physical therapist who was working at the clinic or rehabilitation center where the participants received the physical therapy program, was responsible for operating the IFC machine (Zimmer Soleo Galvab).
Participants in the IFC group were told that they would receive an electrical stimulation treatment for pain relief. They were also told that they would feel a strong tingling but comfortable sensation in the shoulder during the electrical stimulation. The parameters of the interferential current were set. The medium frequency of the interferential current was 4000Hz and 4100Hz to produce the amplitude-modulated frequency at 100Hz in vector mode.11 The current intensity was adjusted to a level that induced a strong tingling sensation.22 The intensity level was adjusted to ensure that participants maintained the same feeling throughout the treatment.23 The stimulation time was set at 20 minutes.24
For the placebo group, participants were told that they would receive an electrical stimulation treatment for pain relief and that they may or may not feel a very light tingling sensation in the shoulder during the electrical stimulation. A procedure similar to that performed in the IFC group was followed, except the lead wires of the equipment were disconnected and were unable to deliver the interferential current. The jack of the output was covered throughout the experiment.25
After the treatment, all pretreatment parameters were immediately reassessed by the first investigator. After finishing the program, all participants were sent back to their physical therapist and received their conventional physical therapy program.
Data analysis
Data analyses were performed with SPSS for Windows.c The descriptive statistics were used to describe the demographic data and clinical characteristics of the participants. The independent t test for continuous data and the chi-square test for noncontinuous data were used to determine baseline group differences. A 2-way mixed analysis of variance was used to examine the main effects and interactions of the independent factors on pain and pain-free PROM, group (IFC and placebo), and time (pretreatment and posttreatment). A pairwise comparison was carried out with Bonferroni corrections to identify the direction of pain and pain-free PROM changes. The minimum clinically significant difference between group means and between time means was set at 2 points for the NRS for pain26 and 4.5° for PROM of the shoulder. For all comparisons, the significance level was set at P<.05.
Results
Characteristics of participants
Thirty patients with HSP (12 men, 18 women) participated in this study. No adverse effects from the IFC treatments were reported. Their pain duration ranged from 14 to 85 days. There was no significant difference in the demographic data or clinical characteristics between the groups (P> .05), as shown in Table 1, Table 2. At baseline, all participants in both groups reported no pain at rest. The pretreatment parameters including pain intensity during the most painful movement and the pain-free PROM of the shoulder at baseline were not different between groups (P> .05) (table 3).
| Variables | IFC (n=15) | Placebo (n=15) | P |
|---|---|---|---|
| Age (y) | 65.87±9.35 | 67.13±10.84 | .73 |
| Sex | |||
| Male | 6 (40.00) | 6 (40.00) | 1.00 |
| Female | 9 (60.00) | 9 (60.00) | |
| Hemiplegic side | |||
| Left | 7 (46.67) | 8 (54.33) | .72 |
| Right | 8 (54.33) | 7 (46.67) | |
| Hemiplegia etiology | |||
| Thromboembolic | 7 (46.67) | 10 (66.67) | .27 |
| Hemorrhagic | 8 (54.33) | 5 (33.33) | |
| Hemiplegic duration (d) | 95.73±28.22 | 103.87±43.21 | .55 |
| Pain duration (d) | 57.73±15.25 | 61.40±19.33 | .57 |
NOTE. Values are mean ± SD, n (%), or as otherwise indicated.
| Variables | IFC (n=15) | Placebo (n=15) | P |
|---|---|---|---|
| Brunnstrom stage | |||
| Stage 1 | 9 (60.00) | 9 (60.00) | 1.00 |
| Stage 2 | 6 (40.00) | 6 (40.00) | |
| Motor Assessment Scale (item 6: upper arm function) | |||
| Scale 0 | 13 (86.67) | 12 (80.00) | .62 |
| Scale 1 | 2 (13.33) | 3 (20.00) | |
| Shoulder clinical subluxation | |||
| Yes | 15 (100.00) | 15 (100.00) | 1.00 |
| No | 0 (0.00) | 0 (0.00) | |
| Shoulder flexor tone | |||
| Grade 0 | 10 (66.67) | 9 (60.00) | .70 |
| Grade 1 | 5 (33.33) | 6 (40.00) | |
| Shoulder extensor tone | |||
| Grade 0 | 14 (94.33) | 11 (73.33) | .14 |
| Grade 1 | 1 (5.67) | 4 (26.67) | |
| Shoulder abductor tone | |||
| Grade 0 | 13 (87.67) | 10 (66.67) | .20 |
| Grade 1 | 2 (13.33) | 5 (33.33) | |
| Shoulder adductor tone | |||
| Grade 0 | 13 (87.67) | 11 (73.33) | .36 |
| Grade 1 | 2 (13.33) | 4 (26.67) | |
| Shoulder internal rotator tone | |||
| Grade 0 | 13 (87.67) | 9 (60.00) | .10 |
| Grade 1 | 2 (13.33) | 6 (40.00) | |
| Shoulder external rotator tone | |||
| Grade 1 | 14 (94.33) | 11 (73.33) | .14 |
| Grade 2 | 1 (5.67) | 4 (26.67) | |
NOTE. Values are n (%).
| Variables | IFC (n=15) | Placebo (n=15) | P |
|---|---|---|---|
| Pain intensity (NRS) | |||
| On the most painful movement | 6.73±1.03 | 6.27±1.22 | .29 |
| Pain-free PROM of the shoulder (deg) | |||
| Flexion | 131.23±18.15 | 119.65±23.01 | .14 |
| Extension | 36.59±2.46 | 35.33±3.00 | .23 |
| Abduction | 113.89±30.20 | 112.15±25.89 | .87 |
| Adduction | 33.13±4.23 | 33.43±3.37 | .84 |
| Internal rotation | 47.40±16.16 | 47.59±15.22 | .97 |
| External rotation | 50.51±17.67 | 52.08±17.04 | .81 |
NOTE. Values are mean ± SD or as otherwise indicated.
Pain intensity
All participants demonstrated no pain at rest posttreatment. For pain during the most painful movement, participants reported a greater reduction in pain intensity after treatment with IFC than with placebo (F1,28=33.64, P< .05, η2=0.5) (table 4).
NOTE. Values are mean ± SD or as otherwise indicated.
Abbreviation: CI, confidence interval.
∗Significant difference between pre- and posttreatment (P<.05).
†Significant difference between IFC and placebo at posttreatment (P<.05).
Pain-free PROM of the shoulder
Participants in the IFC group had greater pain-free PROM posttreatment for flexion (F1,28=32.57, P< .01, η2=0.5), abduction (F1,28=50.52, P< .01, η2=0.4), internal rotation (F1,28=16.17, P< .01, η2=0.3), and external rotation (F1,28=23.30, P< .01, η2=0.4) compared with the placebo group (table 5).
NOTE. Values are mean ± SD or as otherwise indicated.
Abbreviation: CI, confidence interval.
∗Significant difference between pre- and posttreatment (P<.05).
†Significant difference between IFC and placebo at posttreatment (P<.05).
Discussion
To our knowledge, this is the first study that has compared the immediate effects of IFC on shoulder pain and pain-free PROM of the shoulder in people with HSP. The results of this study revealed that IFC is an effective modality for pain management in people with HSP. Pain during the most painful movement was reduced, and the pain-free PROM of the shoulder was also increased in the directions that were previously painful.
In this study, the painful movements of the shoulder reported by all participants included flexion, abduction, internal rotation, and external rotation. One of these directions was also reported as the most painful movement when the shoulder was passively moved. This pain contributed to the limited range of shoulder motion in the related directions. These HSP characteristics are in accordance with the study by Lo et al27 in 2003. They reported that the shoulder movements were restricted in these directions.
In the present study, the placebo group also had a significant pain reduction during the most painful movement. However, this pain reduction was not clinically significant. This placebo effect was consistent with the study13 using IFC and placebo treatments for the management of knee pain. The authors found that the IFC and placebo groups experienced significantly decreased pain after 10 treatment sessions. In addition, previous evidence suggested that the placebo effect would operate mainly on the affective component of pain and would contribute to the effect of treatment as much as 27%.28 In this study, participants in the placebo group were told that they received electrical stimulation therapy. Thus, they might perceive that they received treatment. This perception could lead to a positive attitude toward the treatment. This finding provides additional evidence that the placebo effect should not be abandoned, particularly because this study was measuring an analgesia effect.
This study found that the IFC group demonstrated a greater reduction in pain during the most painful movement than the placebo group, with a large effect size. Previous studies have shown that IFC has an analgesic effect and reduces pain in a variety of conditions such as knee pain13 and frozen shoulder.12 However, the method by which IFC produces an analgesic effect is unclear. It has been hypothesized that the analgesic effect produced by IFC could be similar to that of transcutaneous electrical nerve stimulation.29
In addition, the IFC and placebo groups showed significantly increased PROM of the shoulder in all directions after treatment. These increases were from .85° to 15.80° in the IFC group, and .63° to 3.31° in the placebo group. However, the most notable improvement in the PROM of the shoulder after treatment in the placebo group did not meet clinical significance even in the best range-of-motion improvement (shoulder abduction) (see table 5). According to the minimum clinically significant difference, the amount of acceptable improvement (as a clinical change) in this study was more than 4.5°.
These results suggest that people with HSP gained relief with IFC treatment because the participants reported immediate short-term pain relief and experienced improved PROM. In addition, there are no known adverse effects of IFC treatment in this patient population or restrictions on the frequency or duration of the treatment. Hence, clinical IFC treatment should be considered as an alternative or complementary intervention for pain relief in people with HSP. However, this study did not investigate the long-term effects of IFC treatment or perform follow-up reassessments. Therefore, further studies are needed to examine the long-term effects of IFC, as well as the number of IFC treatment sessions needed for HSP management.
One challenge in people with HSP is the progressive loss of PROM, which seems to be associated with an increase in pain. Thus, it may be better to maintain or restore PROM through a combination of IFC treatment and PROM activities to achieve long-term benefits. For example, the use of IFC before a functional training program should create an advantage from the immediate effects of IFC treatment in reducing pain and enhancing increased pain-free PROM. People with HSP may increase their participation in rehabilitation programs because they will experience less pain.
Study limitations
The results of this study should be interpreted with caution because of a few limitations. First, the characteristics of the participants in this study met specific criteria. Hence, the ability to generalize the results of this study to the stroke population is limited. Second, this study only investigated the immediate effects of IFC treatment. Thus, the long-term effects of IFC treatment in people with HSP remain unknown.
Conclusions
The present study revealed the short-term effects of IFC treatment. IFC treatment was effective in relieving pain during movement and also increased the pain-free PROM of the shoulder in people with HSP.
Suppliers
- a.Digital Angle Rule; Moore & Wright, 32 Leeds Old Rd, Bradford, West Yorkshire BD3 8HU.
- b.Zimmer MedizinSysteme GmbH, Junkersstraße 9, D-89231 Neu-Ulm, Germany.
- c.Version 23; SPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL 60606.
Acknowledgments
We thank the staff of the institutional physical therapy clinic and neurologic rehabilitation center for the participant recruitment and operation the IFC machine.
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