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Immediate Effects of Transcutaneous Electrical Nerve Stimulation on Pain and Physical Performance in Individuals With Preradiographic Knee Osteoarthritis: A Randomized Controlled Trial
Department of Physical Therapy, Human Health Sciences, Graduate School of Medicine, Kyoto University, Kyoto, JapanDepartment of System Design Engineering, Keio University, Yokohama, JapanJapan Society for the Promotion of Science, Tokyo, Japan
To investigate the effect of transcutaneous electrical nerve stimulation (TENS) on knee pain and comprehensive physical function in preradiographic knee osteoarthritis.
Design
A single, participant-blinded, randomized controlled trial (RCT) with pre-post design.
Setting
University research laboratory.
Participants
Patients with knee pain belonging to Kellgren–Lawrence grade 0 or 1 (N=50; aged 50-69y) were randomly assigned to the TENS (n=25) and sham-TENS groups (n=25).
Interventions
All participants wore the TENS device under the patella of the symptomatic knee. After measurement, the TENS devices in the TENS group were turned on, and those in the sham-TENS group were not connected.
Main Outcome Measures
The primary outcome measures included the stair climb test, timed Up and Go (TUG) test, 6-minute walk test (6MWT), and knee pain evaluated using the visual analog scale (VAS) for stair climb test, TUG test, and 6MWT. Secondary outcomes included knee extensor strengths and the 2-step test and stand-up test from the locomotive syndrome risk test.
Results
Multiple regression analysis revealed that TENS intervention significantly improved the walk distance and VAS score of the 6MWT, after adjusting for premeasurement data (distance; P=.015, VAS; P=.030).
Conclusions
Use of TENS improved the VAS score for pain and the distance walked in the 6MWT for individuals with Kellgren–Lawrence grade 0 or 1 of the knee. Thus, TENS may be effective for long-distance walking in patients with preradiographic knee osteoarthritis.
A previous study reported that 27.8% of individuals aged 45 years or older had a prevalence of radiographic knee OA (Kellgren–Lawrence [K/L] grade of at least 2 in at least 1 knee) and 43.3% had a symptomatic knee (pain, aching, or stiffness in at least 1 knee).
Prevalence of knee symptoms and radiographic and symptomatic knee osteoarthritis in African Americans and Caucasians: the Johnston County Osteoarthritis Project.
To date, no useful treatment or preventive measures for knee OA are available; thus, pain management is the main therapy.
Transcutaneous electrical nerve stimulation (TENS) is a commonly used conservative treatment method that is effective in alleviating the pain in knee OA.
Comparison of intra-articular hyaluronic acid injections with transcutaneous electric nerve stimulation for the management of knee osteoarthritis: a randomized controlled trial.
However, some randomized controlled trials (RCTs) or systematic reviews found no significant differences in knee pain between patients who received TENS, and the sham group.
Comparison of the efficacy of transcutaneous electrical nerve stimulation, interferential currents, and shortwave diathermy in knee osteoarthritis: a double-blind, randomized, controlled, multicenter study.
Thus, whether TENS is effective for knee OA remains unclear. Moreover, the main outcome of these previous studies on TENS is knee pain, which was measured using instruments such as the visual analog scale (VAS) or Western Ontario and McMaster Universities Arthritis Index scale (WOMAC). Decrease in pain can improve physical function; however, limited studies have exhaustively measured the effect of decrease in pain on physical function through factors such as muscle strength, speed, endurance, and balance. Further, few studies have revealed the effect of TENS intervention during physical functional tests.
We focused on the locomotive syndrome risk test as an exhaustive physical function test. In 2007, the Japanese Orthopaedic Association (JOA) proposed the term locomotive syndrome, which refers to a decline in locomotive ability caused by diseases of the bones, joints, muscles, and nerves.
Knee OA is one of the diseases that causes locomotive syndrome; thus, the locomotive syndrome risk test can be an important measure of functional ability.
Several studies on knee OA have revealed discordance between radiographic evaluation and the somatic symptoms of this condition. The K/L grade is a common radiographic evaluation system for knee OA; it involves classification of knee OA according to the severity of bone deformity.
Prevalence of abnormalities in knees detected by MRI in adults without knee osteoarthritis: population based observational study (Framingham Osteoarthritis Study).
Thus, even individuals with K/L grade 0 or 1 (preradiographic OA) may have knee pain or inadequate function. Additionally, individuals with preradiographic OA, particularly with K/L grade 1, have been predicted to progress to at least grade 2.
Can we identify patients with high risk of osteoarthritis progression who will respond to treatment? A focus on epidemiology and phenotype of osteoarthritis.
Thus, to prevent the progression of knee OA or to avoid the functional disability associated with it, preradiographic OA is an important stage for intervention or treatment. However, studies on the treatment of or physical function in preradiographic OA are lacking. Most studies on TENS for knee OA have investigated only patients with K/L grade ≥2; no study in individuals with preradiographic OA has been conducted. Therefore, this study aimed to investigate the effect of TENS on comprehensive physical function and knee pain during physical functional tests for individuals with preradiographic OA. In addition, we sought to examine the hypothesis that TENS reduces knee pain during physical function tests in individuals with preradiographic OA and improves the physical function of individuals with preradiographic OA, thus reducing knee pain.
Methods
Study design
This was a single, participant-blinded, RCT with a prepost design, in which 2 parallel groups were compared, namely the TENS group and the control (sham-TENS) group. The study protocol was approved by the institutional review board. Written informed consent was obtained from all participants before enrollment.
Participants
Information regarding this study was posted on a website, and interested individuals answered a questionnaire concerning their physical condition. Whether the participants met the selection criteria was assessed via the questionnaire responses (supplemental appendix S1, available online only at http://www.archives-pmr.org/).
Assessments
All outcome measure assessments and radiographic studies were performed at baseline. After a 30-minute rest, participants were re-evaluated while wearing the TENS device. The primary outcome measures included the stair climb test, timed Up and Go (TUG) test, 6-minute walk test (6MWT), and knee pain evaluated using the VAS for the stair climb test, TUG test, and 6-minute walk test. The secondary outcomes include knee extensor strengths and the 2-step test and the stand-up test in the locomotive syndrome risk test.
The stair climb test, TUG test, and 6MWT were conducted according to OARSI-recommended performance-based tests.
Knee pain and disability characteristics at baseline were evaluated using a subcategory of the Japanese Knee Osteoarthritis Measure (JKOM).
Demographic data
Data on height, weight, age, and sex were reported by the participants themselves. Body mass index was calculated by dividing the weight by the square of the height.
Radiographic evaluation
Anteroposterior radiography of the index knees was performed in fully extended weight-bearing and foot map positions. The beam was positioned parallel to the floor. The radiographs were assessed by an experienced physician with more than 10 years of clinical experience, using the original version of the K/L classification system.
An 11-step stairway with a step height of 17 cm was used. Participants began with both feet on the bottom landing, then ascended and descended the stairway as fast as possible, and finally stopped with both feet back on the bottom landing while availing handrail support, if required. Time recording was started when the participant was signaled to start and ended when the participant returned with both feet on the ground. The total time was recorded to the nearest one hundredth of a second. Two trials were performed, and the faster time of the 2 trials was recorded. The minimal detectable change (MDC) with 95% confidence interval (CI) was 2.77 seconds.
Reliability and measurement error of the Osteoarthritis Research Society International (OARSI) recommended performance-based tests of physical function in people with hip and knee osteoarthritis.
In this test, the participant sat down at first and then stood up when given the signal to start. As fast as possible, the participant walked 3 meters toward a cone on the floor, circled it, walked back 3 more meters toward a chair, and finally sat down. Timing began on the signal to start and ended when the participant completely sat down with their back resting on the backrest of the chair. Two trials were performed, and the faster time of the 2 trials was recorded to the nearest one hundredth of a second. The MDC with 95% CI was 1.39 seconds.
Reliability and measurement error of the Osteoarthritis Research Society International (OARSI) recommended performance-based tests of physical function in people with hip and knee osteoarthritis.
In the 6MWT, the participants walked as far as they could within 6 minutes. They were not allowed to carry a watch or provided feedback during the trial. Although rest periods were allowed, time recording continued. The participants were provided encouragement at 1-minute intervals. Their performance was measured as the total distance traveled, and was recorded as an integral number. The MDC with 95% CI was 50.23 m.
Reliability and measurement error of the Osteoarthritis Research Society International (OARSI) recommended performance-based tests of physical function in people with hip and knee osteoarthritis.
The maximum isometric knee extensor strengths were measured using a handheld dynamometer (HHD), which is the validated method in a previous research on elderly individuals who are prone to falls.
The maximum force was recorded in Newtons (N), and testing was repeated for 2 measurements. The measurements were started once the participants were seated on the therapy bed. The knee was placed at 90° flexion, with the HHD being attached 10 cm proximal to the lateral malleolus and held in place with an inelastic strap looped around the therapy bed and fastened. The length of the straps allowed for an isometric contraction to be performed, with the knee at 90° flexion. The participants were instructed to extend their leg for 5 seconds. Strong verbal encouragement was provided to ensure maximal effort. To provide moment value (Nm), the lever arm (length of the femur or tibia) between the knee joint and HHD was manually measured and subsequently normalized to their mass (Nm/kg). The averaged value of 2 measurements was used for statistical analysis.
Locomotive syndrome risk test
The locomotive syndrome risk test includes the 2-step test, stand-up test, and 25-question risk assessment. Each test detects locomotive syndrome stages 1 (the beginning of decreased locomotive ability) and 2 (progression of decreased locomotive ability), and participants who fulfill the criteria for a test are classified accordingly as stage 1 or 2. In this study, the 2-step test and stand-up test were selected as the comprehensive physical function tests.
Locomotive syndrome risk test: 2-step test
Here, stride length is measured to assess walking ability, including muscle strength, balance, and flexibility of the lower limbs. The starting line is determined, and participants stand with the toes of both feet behind this line. They take 2 long steps (as long as possible) and then align both their feet. Subsequently, the length of the 2 steps from the starting line to the toes is measured. Two trials were performed in this study, and the longer distance of the 2 trials was recorded. The 2-step test score was calculated as follows: length of the 2 steps (cm)/participant height (cm). Locomotive syndrome stage 1 was defined as a score <1.3, and stage 2 was defined as a score <1.1.
Locomotive syndrome risk test: stand-up test
This test requires the participant to stand up on 1 or both legs from a seat at a specified height. For this test, 4 seats are set up at different heights (40, 30, 20, and 10 cm). First, the participants sit on the 40-cm high seat with arms folded. If they can stand up on both legs, they then attempt to stand on 1 leg. If they can stand up on both their right and left legs, they pass the height level. The participants then repeat the trial at the next seat height, and the trials are performed in the order of descending height. Locomotive syndrome stage 1 is defined as the inability to stand up from a height of 40 cm on either leg, and stage 2, as the inability to stand up from a height of 20 cm on both legs.
VAS score for knee pain
The mean knee pain during the stair climb test, TUG test, and 6MWT was measured using the VAS.
Participants recorded their level of knee pain by drawing a vertical mark between the ends of a 10-cm horizontal line. The 0-cm end and the 10-cm end represented no pain and the most extreme pain, respectively. The distance from the 0-cm end to the drawn mark was recorded to the first decimal place. The MDC with 95% CI was 2.8 cm.
was used to evaluate baseline knee pain and disability. The JKOM is a self-reported evaluation system comprising 25 questions and a VAS score for current knee pain. It assesses pain and stiffness, activities of daily living, participation in social activities, and general health conditions. Each question is scored on a 4-point scale, and the maximum possible score is 100 points in a person-specific assessment. The concurrent and construct validities of the JKOM have been established against the WOMAC and the Medical Outcomes Study 36-item Short-Form Health Survey, respectively.
After baseline assessment, all participants wore the TENS devicea under the patella of the symptomatic knee, with the knee flexed at 90°. The following TENS parameters were applied: sweep mode from 1 to 250 Hz, symmetrical biphasic pulse, and a pulse width of 60 μs.
Effect of modulated-frequency and modulated-intensity transcutaneous electrical nerve stimulation after abdominal surgery: a randomized controlled trial.
The intensity in the TENS group was gradually increased and limited by the participant’s perception of a strong but comfortable, nonpainful tingle immediately below the visible motor threshold. The intensity was gradually increased during the intervention, as sensation decreases owing to habituation.
Is mechanical pain threshold after transcutaneous electrical nerve stimulation (TENS) increased locally and unilaterally? A randomized placebo-controlled trial in healthy subjects.
For participants in the sham-TENS group, sham stimulation of gradually increasing intensity of a nonconnected channel was applied, and participants were informed that owing to the expected effect being below the sensory threshold, they would not perceive any currents. The postassessment measurements were then carried out with the participants wearing the TENS device. All interventions were performed by physical therapists with clinical experience in musculoskeletal medicine.
Statistical analyses
Student’s t test or chi-square test was used to assess for significant baseline differences in characteristics between the TENS and sham-TENS groups. The Shapiro–Wilk test was used to confirm the statistical normality of outcome variables. To identify within-group differences, paired samples t tests or Wilcoxon signed rank test for continuous variables and chi-square test for categorical variables were used. Baseline-adjusted multiple regression analysis models were used to evaluate between-group differences for outcomes that had significant within-group differences.
P<.05 was considered statistically significant, and all data were analyzed using the JMP Pro 13.0.0b (SAS Institute, Cary, NC).
Results
In total, 59 participants were evaluated, 9 of whom (16.9%) were excluded because of mild radiographic OA (K/L grade=2). Thus, 50 participants (n=25 in each group) were finally included (fig 1).
Table 1 shows the baseline characteristics of the 50 participants. No difference was observed in the baseline characteristics between the groups (supplemental table S1 [available online only at http://www.archives-pmr.org/]).
Table 1Physical characteristics of TENS and sham TENS group subjects
Characteristic
TENS (n=25)
Sham (n=25)
P
Height, cm
161.0±7.53
160.1±8.38
.70
Weight, kg
55.9±7.94
58.4±12.06
.40
BMI, kg/m2
21.6±2.62
22.6±3.46
.23
Age, y
59.1±6.13
57.9±5.07
.45
Women, n (%)
19 (76.0)
16 (64.0)
.35
K/L grade 0, n (%)
11 (44.0)
12 (48.0)
.78
K/L grade 1, n (%)
14 (56.0)
13 (52.0)
JKOM
15.6±8.85
12.5±6.78
.17
Baseline NRS
5.40±1.15
5.16±1.31
.50
NOTE. Continuous data are expressed as mean ± SD (Student t test). Categorical data are expressed as n (%) (chi-square test).
Table 3 shows the results of each outcome between the groups, adjusted for premeasurement data as baseline. Multiple regression analysis revealed that compared to sham-TENS, TENS intervention significantly improved the walk distance and VAS score of the 6MWT, after adjusting for premeasurement data.
No adverse effect was noted with the TENS or sham-TENS treatment.
Discussion
The most important finding of the present study was that a significantly immediate effect of TENS was observed in terms of improvement in the walk distance and VAS score of 6MWT in participants with preradiographic knee OA.
TENS is effective for nociceptive pain mechanisms based on the gate control theory of pain
In this study, TENS intervention was considered to reduce knee movement-evoked pain and increase walking distance. Thus, participants in the TENS group may be able to walk longer distances in the postassessment period. In addition, compared to TUG or timed-stand test, the 6MWT was shown to be more responsive after physiotherapy in patients with knee OA.
The 6MWT takes a longer time and is a high-intensity test; thus, participants may tend to experience knee pain. In this study, the VAS score of 6MWT was higher than that of any other physical task, which may influence the performance in 6MWT. This result is consistent with a previous finding that whole body vibration exercise for patients with knee OA significantly improved the score of 6MWT; however, no significant change was noted in the TUG score.
Effects of whole body vibration exercise associated with quadriceps resistance exercise on functioning and quality of life in patients with knee osteoarthritis: a randomized controlled trial.
A previous study reported that the minimal clinically important difference of VAS score is 1.1 point in patients who have a VAS pain of 3.0 cm or lower.
Thus, decrease in the VAS pain after intervention in the TENS group was nearly equal to the minimal clinically important difference; however, the difference in the sham-TENS group did not reach this level. If the minimal clinically important difference is considered as a standard, this result would be clinically meaningful.
No significant difference was observed in the stair climb test, TUG, and knee extensor strengths between the groups. Patients with knee OA tend to experience knee pain while using the stairs owing to weight-bearing and knee bending.
Thus, stair climb test was selected for the outcome of this study, as it was considered sufficiently difficult for participants with preradiographic knee OA. However, participants felt mild pain during the stair climb test or TUG test, with a VAS score <2. Stair climb test and TUG test are shorter-duration tests than 6MWT is, and they mainly assess speed agility; thus, mild pain that reflects a VAS score <2 may carry little significance for the 2 tests. This result supports a previous finding that no significant effect was observed in the use of TENS in the stair climb test or TUG for patients with knee OA.
Would the addition of TENS to exercise training produce better physical performance outcomes in people with knee osteoarthritis than either intervention alone?.
As per OARSI guidelines, the recommendation of TENS is uncertain; no optimal size has been reported owing to the low methodological quality and high heterogeneity among the included trials.
Additionally, several RCTs revealed no statistically significant difference in knee pain between participants undergoing the TENS and a sham-TENS procedure.
Comparison of the efficacy of transcutaneous electrical nerve stimulation, interferential currents, and shortwave diathermy in knee osteoarthritis: a double-blind, randomized, controlled, multicenter study.
Would the addition of TENS to exercise training produce better physical performance outcomes in people with knee osteoarthritis than either intervention alone?.
However, participants of a previous RCT had knees with K/L grades above 2, unlike the current study. Patients with lower grades of knee OA were associated with a higher grade of efficacy of electroacupuncture treatment.
Therefore, individuals with K/L grades 0-1 may have characteristics different from those of individuals with K/L grades above 2. Moreover, TENS may be more effective for individuals with preradiographic knee OA with a lower K/L grade than for patients with knee OA with bone deformities.
Study limitations
This study has some limitations. First, we did not set a follow-up period with the participants after evaluation. Second, the participants were self-motivated, as they applied by obtaining information regarding this study on the website; thus, a selection bias may exist. Finally, as participants had preradiographic OA, the results cannot be applied to mild or severe OA.
Conclusions
Compared to sham-TENS, TENS improved the walk distance and VAS score of 6MWT in patients with preradiographic knee OA, suggesting that TENS effectively increases walk distance while reducing pain, particularly in preradiographic knee OA.
Suppliers
a.
HV-F710; Omron Healthcare Co., Ltd.
b.
JMP Pro 13.0.0; SAS Institute.
Supplemental File 1. Methods
Inclusion and exclusion criteria
The inclusion criteria for the study were as follows: (1) individuals aged 50 years or older
0–1 for one or both knees, as evaluated using weight-bearing anteroposterior radiographs; and (3) those experiencing an average pain rated between 4 and 9 on a numeric rating scale (0–10 points)
. Individuals were excluded if they: (i) had symptomatic knee OA with K/L grade 2 or above, (ii) had a history of knee surgery or had received an intra-articular corticosteroid or hyaluronic acid injection within 6 months prior to enrollment
, (iii) had a history of knee joint replacement or tibial osteotomy, (iv) were undergoing physical therapy, (v) had any other major joint pain (e.g., back, hip, or ankle) that could limit functional ability, (vi) had contraindications to TENS (pacemakers, dermatological conditions, and abnormal sensation in the knees), (vii) had severe medical or nervous conditions (e.g., chronic obstructive pulmonary disease, cardiovascular disease, arteriosclerosis obliterans, cerebrovascular accident, lumber disc herniation, and rheumatoid arthritis), (viii) did not utilize stairs in daily living, and (ix) were unable to walk without ambulatory assistive devices. In patients in whom both the knees were involved, the more painful knee (as identified by the participant) was evaluated.
Sample size calculation
Sample size was calculated based on the data provided by Chen et al.
Comparison of intra-articular hyaluronic acid injections with transcutaneous electric nerve stimulation for the management of knee osteoarthritis: A randomized controlled trial.
, who found a significant decrease in pain (1.14 cm on a 0–10 VAS) in patients with knee OA who underwent TENS therapy (standard deviation [SD]=1.78 cm) compared to that in patients who did not undergo TENS therapy (SD=1.97 cm). We used the G*Power program (Heinrich–Heine–Universität Düsseldorf, Düsseldorf, Germany)
with a power of 80% and a significance level of 0.05, which yielded a sample size of 24 participants in each group.
Randomization
Participants were randomly allocated to the TENS or the sham-TENS group, using stratified and block randomization. Studies have shown that female patients have a lower sensory threshold and respond to electrical stimulation differently from male patients
Is mechanical pain threshold after transcutaneous electrical nerve stimulation (TENS) increased locally and unilaterally? A randomized placebo- controlled trial in healthy subjects.
Allocations were performed by an independent researcher who did not influence any assessments in this study. The assessors were blinded to the randomization until the outcome assessments were completed. To conceal randomization, consecutively numbered, sealed, opaque envelopes were prepared by a researcher who had no other involvement in the study. The envelopes were stored at a locked location, and then opened in sequence within each stratum to reveal the group allocation.
Prevalence of knee symptoms and radiographic and symptomatic knee osteoarthritis in African Americans and Caucasians: the Johnston County Osteoarthritis Project.
Comparison of intra-articular hyaluronic acid injections with transcutaneous electric nerve stimulation for the management of knee osteoarthritis: a randomized controlled trial.
Comparison of the efficacy of transcutaneous electrical nerve stimulation, interferential currents, and shortwave diathermy in knee osteoarthritis: a double-blind, randomized, controlled, multicenter study.
Prevalence of abnormalities in knees detected by MRI in adults without knee osteoarthritis: population based observational study (Framingham Osteoarthritis Study).
Can we identify patients with high risk of osteoarthritis progression who will respond to treatment? A focus on epidemiology and phenotype of osteoarthritis.
Reliability and measurement error of the Osteoarthritis Research Society International (OARSI) recommended performance-based tests of physical function in people with hip and knee osteoarthritis.
Effect of modulated-frequency and modulated-intensity transcutaneous electrical nerve stimulation after abdominal surgery: a randomized controlled trial.
Is mechanical pain threshold after transcutaneous electrical nerve stimulation (TENS) increased locally and unilaterally? A randomized placebo-controlled trial in healthy subjects.
Effects of whole body vibration exercise associated with quadriceps resistance exercise on functioning and quality of life in patients with knee osteoarthritis: a randomized controlled trial.
Would the addition of TENS to exercise training produce better physical performance outcomes in people with knee osteoarthritis than either intervention alone?.
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