Transcutaneous electrical nerve stimulation (TENS) and extracorporeal shockwave therapy (ESWT) in lateral epicondylitis: a systematic review and meta-analysis

Abstract

Background

Consensus has not yet been reached regarding the optimal nonoperative treatment of lateral epicondylitis. Physiotherapy is often utilized, yet the specific modalities used can vary significantly, making this treatment arm quite broad. The role and efficacy of passive physiotherapy by way of transcutaneous electrical nerve stimulation (TENS) and extracorporeal shockwave therapy (ESWT) are not well understood. The purpose of this systematic review and meta-analysis was to compare transcutaneous electrical nerve stimulation (TENS) and extracorporeal shockwave therapy (ESWT) with no active treatment.

Methods

MEDLINE, Embase, and Cochrane were searched through till September 20, 2021. All English-language randomized trials comparing passive electrophysiotherapy treatments compared with no active treatment/placebo of patients >18 years of age with lateral epicondylitis with minimum 6-month follow-up were included.

Results

In the pooled analysis of 2 trials, ESWT provided no benefit compared to no active treatment for pain (−7.063, 95% confidence interval [CI]: −19.16 to 3.89) or function (standardized mean difference [SMD]: 0.03, 95% CI: −0.31 to 0.38, I² = 0%). TENS showed no improvement in function compared with control with a mean difference in PRTEE scores of 2.93 points (95% CI −8.30 to 2.43) at 12 months, nor were differences seen in pain scores at 12 months (P = .139).

Discussion

The available evidence does not support the use of passive electrophysiotherapy modalities, TENS or ESWT in the treatment of lateral epicondylitis.

The optimal management of lateral epicondylitis remains controversial. Despite a lack of high-level evidence to inform clinical decision-making, nonoperative management of this challenging condition represents first-line treatment. Lateral epicondylitis is common as it affects 1%-3% of the population.⁴ Nonoperative treatment represents first-line therapy and may include no active treatment, strengthening, extracorporeal shockwave therapy (ESWT), transcutaneous electrical nerve stimulation (TENS), and injections of corticosteroid, platelet-rich plasma (PRP), and autologous blood (AB).^9,15,24 Surgery may be considered when nonoperative treatment fails.³

Although there is consensus that nonoperative modalities should represent first line treatment, guidelines informing the optimal approach are not well established.^9,10,20 Evidence is lacking regarding the superiority of one nonoperative treatment over another as past systematic reviews have not reached definitive conclusions.^6,22 Past systematic reviews have often concentrated on various injection treatments without considering other common forms of treatment such as the many physiotherapy modalities.^12,15 A meta-analysis by Weber et al concluded that there was insufficient evidence to support physiotherapy for the treatment of tennis elbow.²⁵ Yet, a meta-analysis by Dingemanse et al demonstrated benefit with electrophysiotherapy but included short-term studies in the order of weeks.¹¹ These inconsistent and short-term findings make interpretation of the literature difficult and hinder the clinicians’ ability to counsel patients effectively.

The uncertainty surrounding the efficacy of various available nonoperative interventions makes the selection of appropriate treatments difficult. The aim of this systematic review and meta-analysis was to evaluate pain and functional outcomes of electrophysiotherapy modalities of TENS and ESWT, compared with no active treatment or placebo controls in lateral epicondylitis.

Methods

As inclusion criteria, we identified English-language randomized controlled trials (RCTs) comparing passive electrophysiotherapy treatments with no active treatment or placebo control in patients aged 18 years or older with lateral epicondylitis. Studies with a minimum follow-up duration of 6 months post intervention were considered. Non-randomized studies/observational studies were excluded, as were studies that included other forms of physiotherapy such as injections. Studies that compared electrophysiotherapy to another form of active treatment were also excluded. This study adheres to the standards of the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) statement.²¹ The study was registered at the PROSPERO registry of systematic reviews (CRD42022320943).

Review eligibility criteria were based on the Population-Intervention-Comparators-Outcomes-Study (PICOS) design framework. We included primary studies meeting the following criteria:

• Population: Randomized controlled trials enrolling patients above 18 years of age with lateral epicondylitis receiving passive physiotherapy treatments.

• Interventions

  • Extracorporeal shockwave therapy (ESWT)
  • Transcutaneous electrical nerve stimulation (TENS)

• Comparators: No active treatment or placebo control

• Outcomes: Minimum 6-month follow-up of:

  • Post-intervention pain (Visual Analog Scale)
  • Functional outcomes scores (eg, Patient-Rated Tennis Elbow Evaluation, Disabilities for the Arm, Shoulder, and Hand)

Information sources and search strategy

The search strategies were developed by an experienced medical information specialist in consultation with the investigators. Ovid MEDLINE, including Epub Ahead of Print and In-Process & Other Non-Indexed Citations, Embase Classic+, Embase and the Cochrane Library were searched using the OVID platform. The latest search was performed on September 20, 2021.

Two search strategies were used for pain and function, respectively. Controlled vocabulary (eg, “lateral epicondylitis”) and keywords (eg, “randomized controlled trial, passive physiotherapy”) were utilized. Results were filtered using headings for systematic reviews and RCTs. Vocabulary and syntax were adjusted across databases. The search was restricted to English-language studies with no date restrictions. Animal-only and opinion pieces were removed from the results. The search strategies can be found in Supplements. Existing reviews were inspected to confirm no relevant studies were missed.

Screening and data extraction

Screening was performed by 2 reviewers working independently and in duplicate using eligibility criteria established a priori. Stage 1 screening involved abstract review. Potentially relevant studies were then considered for stage 2 screening with full-text review. Disagreements at any stage were resolved between reviewers via consensus. The study selection process was reported using a PRISMA flow diagram.²¹ References of all included studies were scanned for inclusion by one reviewer. When multiple reports of the same study cohort were published, the most complete set were used, and repeated publications excluded.

A standardized data extraction form from Covidence systematic review software (Veritas Health Innovation, Melbourne, Australia) was used for collecting key study information that included all prespecified data items. Two reviewers extracted the data independently and any discrepancies were resolved via consensus. Information from each study included (but was not limited to) the following: publication characteristics (eg, authors’ names, publication year, and journal), study design traits (cited trial design, clinical setting, duration of follow-up, number of patients randomized and number analyzed for each outcome, occurrence of dropouts, funding source, authors’ conflict of interest, etc.), study population details (patient inclusion and exclusion criteria, age, and sex), comorbidities, and prior treatments. Intervention and comparator specifics (type of treatment) and outcome data (including reported outcome definitions and summary data related to treatment effects (eg, mean change and the corresponding standard error for continuous outcomes, and number of events, and number of total patients for dichotomous outcomes), and reported scales for evaluating the outcomes). Means, if not directly specified were approximated from figures in the primary studies using online tools. The authors’ defined prespecified outcomes of interest were extracted and grouped accordingly for analyses.

Outcomes and prioritization

The Core Outcome Measures in Effectiveness Trials (COMET) initiative does not list a core outcome set for lateral epicondylitis.¹ Therefore, outcome scores of interest were selected via consultation with our clinical experts. The primary outcome of interest was pain, and the secondary outcome of interest included postintervention function. We considered outcome data from baseline to 24 months post-treatment. However, given the short-term nature of included studies, 6 months was chosen as the minimum acceptable time of assessment.

Risk of bias assessment

Risk of bias of included trials were assessed by the Cochrane Risk of Bias Tool (CRBT) for RCTs.¹⁴ Two reviewers carried out assessments independently and resolved disagreements via consensus. All domains of the CRBT for RCTs were considered, including selection bias (sequence generation and allocation sequence concealment), performance bias (blinding of participants and personnel), detection bias (blinding of outcome assessment), attrition bias (incomplete outcome data), and reporting bias (selective reporting). Bias risk was scored as low, moderate, or high, based on study methodology. The quality of included trials was assessed using the Grades of Recommendation, Assessment, Development and Evaluation (GRADE).^2,13 RCTs are assigned a “high” quality as per the GRADE but can be downgraded due to risk of bias, imprecision, inconsistency, indirectness, or publication bias.¹³ An overall grade was then assigned (high, moderate, low, or very low) and graded as per the PICO framework described above and applied to each outcome.

Approaches to evidence syntheses

Criteria for quantitative synthesis

We inspected the characteristics of included studies such as patients’ clinical characteristics (age, sex) and methodologic homogeneity (eg, risk of bias, study design), and summarized them accordingly. A pairwise meta-analysis for the intervention comparison was pursued to explore statistical heterogeneity (based on the I² statistic) with regards to pain and function.

Statistical analysis and assessment of heterogeneity

Data was pooled using Revman 5.4.⁷ The visual analog scale (VAS) was used for pain, while the standardized mean difference (SMD) was used across related functional measures to maximize usage of available data. All pairwise comparisons are expressed with credible 95% confidence intervals. According to Cohen’s effect sizes for interpretation of SMDs, an SMD <0.2 was considered a small effect, 0.2-0.8 a moderate effect, and >0.8 a large effect.⁸ An SMD of 0.5 was considered a clinically significant functional improvement.¹⁹

In addition to inspection of the forest plots, heterogeneity was assessed using the I² statistic with <40% indicating low heterogeneity and >75%, substantial heterogeneity. In the presence of low or absent heterogeneity, fixed effects models were used, and mixed effects models were used if heterogeneity was detected (I² >40%).

Pairwise meta-analyses of each main outcomes of interest were utilized as outlined in the PICO framework described previously.

Results

The search strategies yielded 868 studies, leaving 445 after duplicates were removed. All 445 underwent abstract review and 27 studies were deemed relevant for full text screening. No further studies were added from inspection of past reviews. Of those 27 studies, three were selected for inclusion.^5,18,23 The study flow is summarized in Figure 1. The sample sizes of individual studies ranged from 55 to 241 patients. Follow-up time ranged from 6 to 12 months. Study characteristics are summarized in Table I.

Figure 1.

Flow diagram of search strategy.

Table I.

Study characteristics.

Author, year	Electrophysiotherapy modality	Subjects (n)	Age, y (mean)	Follow-up time, months	Outcome measures
Melikyan, 200318	ESWT	74	43.4	12	VAS, DASH
Staples, 200823	ESWT	55	49.5	6	VAS, DASH
Chesteron, 20145	TENS	241	49.6	12	VAS, PRTEE

ESWT, extracorporeal shockwave therapy; TENS, transcutaneous electrical nerve stimulation; VAS, visual analog scale; DASH, disabilities of the arm, shoulder, and hand; PRTEE, patient-rated tennis elbow evaluation.

In the pooled analysis of two trials (129 randomized patients), ESWT was found to provide no benefit compared to no active treatment or placebo control with regards to pain (−7.063, 95% confidence interval [CI]: −19.16 to 3.89, I² = 0%). ESWT also provided no benefit with regards to function as compared to no active treatment or control (standardized mean difference [SMD]: 0.03, 95% CI: −0.31 to 0.38, I² = 0%). Results are summarized in Table II and Figures. 2 and 3.

Table II.

GRADE summary.

Electrophysiotherapy vs no active treatment for tennis elbow
Certainty assessment							Number of patients		Effect		Certainty
Number of studies	Study design	Risk of bias	Inconsistency	Indirectness	Imprecision	Other considerations	Electro-physiotherapy	No active treatment	Relative (95% CI)	Absolute (95% CI)
Pain
2	randomized trials	serious∗	not serious	not serious	serious†	none	65	64	-	SMD 7.63 SD higher (−19.16 lower to 3.89 higher)	⨁⨁◯◯ Low
Function
2	randomized trials	serious∗	not serious	not serious	serious†	none	65	64	-	SMD 0.03 SD lower (−0.31 lower to 0.38 higher)	⨁⨁◯◯ Low

CI, confidence interval; VAS, visual analog scale; SMD, standardized mean difference; SD, standard deviation.

^∗One study underpowered, and lack of blinding of interventions.

^†Wide confidence intervals.

Figure 2.

Forest plot of electrophysiotherapy versus no active treatment/placebo for pain. Risk of bias legend:  = high risk of bias; no color = unclear risk;  = low risk of bias. SD, standard deviation; CI, confidence interval.

Figure 3.

Forest plot of physiotherapy versus no active treatment for function. Risk of bias legend:  = high risk of bias; no color = unclear risk;  = low risk of bias. SD, standard deviation; CI, confidence interval.

TENS was compared with control group of no active treatment in a trial by Chesterton et al PRTEE scores improved by 2.93 points (95% CI −8.30 to 2.43) at 12 months, thereby indicating a non–statistically significant improvement. Similarly, no differences were seen in pain scores at 12 months, with a P value of .139.

Two studies, Melikyan et al and Staples et al utilized ESWT while the third, Chesterton et al used TENS. Both Melikyan et al and Staples et al included placebo control groups. Staples et al utilized subtherapeutic shocks while Melikyan et al inserted a foam pad medium acting as a reflective barrier between the skin and emitter. Chesterton et al provided a control group with GP advice but no active treatment. Chesterton et al allowed for analgesics to be used in either group at the patient’s discretion while Staples et al allowed either group to utilize stretches and bands at their own discretion.

Using the Cochrane Risk of Bias tool, all studies were found to have a moderate risk of bias. The included studies were downgraded according to the GRADE assessment as they demonstrated wide confidence intervals indicative of imprecision. Specifically, the Chesterton et al trial provided no participant blinding while the Staples et al trial did not satisfy their power requirement. There were no serious methodological concerns with the Melikyan et al study.

Discussion

This systematic review and meta-analysis included three randomized controlled trials comparing passive electrophysiotherapy treatment of lateral epicondylitis to no active treatment or placebo control. We found that TENS and ESWT provided no benefit with respect to pain or functional scores.

These modalities continue to be used in many centers, despite the limited evidence to support their use. We felt it was important to provide an updated analysis of the available literature to determine treatment effectiveness.

These findings complement a prior review performed by our group comparing active physiotherapy (strengthening), injection with corticosteroid, injection with platelet-rich plasma or injection with autologous blood compared with no active treatment or placebo control in lateral epicondylitis.¹⁷ In that review, all treatment modalities also provided no benefit to pain or function. In fact, corticosteroids were found to yield worse pain and functional scores as compared to control.

A recent systematic review and meta-analysis of RCTs by Kim et al comparing nonoperative treatment modalities in lateral epicondylitis included electrophysiotherapy modalities in their analysis.¹⁶ They too found that electrophysiotherapy provided no benefit in terms of pain relief. They did, however, find improved PRTEE and DASH scores. Yet, heterogeneity was moderate and confidence intervals included values below the minimal clinically important difference (MCID) meaning the effect size was small and unlikely to be clinically relevant. Further, their inclusion of electrophysiotherapy included microcurrent therapy instead of the more widely accepted TENS, which emits a higher current. They also included the lesser utilized modality of laser therapy.

A similar review by Dingemanse et al, included a single study on TENS which showed a benefit in pain response but only had two-week follow-up.¹¹ Their included studies investigating ESWT were nearly all short-term, save for the 1-year study by Melikyan et al included in our review.¹⁸

We provide an updated analysis of the lateral epicondylitis literature with respect to the widely used TENS and ESWT modalities, focusing on medium-term results of at least 6 months and beyond. We found no added benefit with respects to pain or function. Prior studies have demonstrated short-term benefit within the 2-8 week timeline, but our goal was to identify sustained benefit beyond this, of which there was not.^11,16

A strength of our review was that we only included RCTs to limit the risk of bias and obtain the highest quality evidence. Further, prior reviews have included studies of short-term follow-up in the order of weeks, but trials included in the current study required a minimum of 6 months follow-up. Additionally, only studies that compared electrophysiotherapy with no active treatment or placebo controls were included to limit bias. Many studies compared treatment modalities against each other with a lack of control group and were therefore excluded. This allows a clear interpretation of the true treatment effect of TENS and ESWT.

A limitation of such stringent inclusion criteria was that only 3 studies were included, and only one investigated TENS. However, this demonstrates the paucity of high-quality data available in the literature and the need to perform a pooled analysis such as this. We recognize the included studies are not recent, and it should be noted that modern equipment and a varying protocol of frequency, energy emitted, pulse time, and total duration could yield differing results. However, there are no such RCTs evaluating this. Although the highest level of evidence was sought, the studies presented a moderate risk of bias given the level of imprecision, moderate heterogeneity, and lack of patient blinding in one trial, and lack of power in another. The total number of patients between all three studies only totaled 370 patients.

Further high-quality randomized controlled trials are required to narrow heterogeneity and increase confidence in the findings of this review. Trials involving modern equipment and varying treatment protocols may show benefit. Increased length of follow-up is also essential as the vast majority of lateral epicondylitis improves over the course of a year and those that do not have undergone operative release, either open or arthroscopic.⁴

Conclusions

This systematic review and meta-analysis shows that the highest quality available evidence does not support the use of passive electrophysiotherapy modalities such as TENS or ESWT in the treatment of lateral epicondylitis. Furthermore, high-quality trials with larger patient numbers and longer-term follow-up should be performed to reduce the heterogeneity of findings.

Acknowledgments

The authors would like to thank Katie McIlquham, clinical research coordinator for assistance with Prospero registration and administrative details. The authors would also like to acknowledge special contributor Ms. Risa Shorr for literature search support.

Disclaimers

Funding: No external funding was received.

Conflicts of interest: The authors, their immediate families, and any research foundation with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.