The Efficacy of Extracorporeal Shock Wave Therapy as a Monotherapy for Achilles Tendinopathy: A Systematic Review and Meta-Analysis

Abstract

Objective

The aim of this systematic review and meta-analysis was to determine the therapeutic efficacy of extracorporeal shock wave therapy (ESWT) for Achilles tendinopathy.

Methods

We searched PubMed, EBSCOHost, Ovid, and Embase for randomized controlled trials. Databases were searched from their inception until the last entry (July 16, 2022). The methodological quality of the randomized controlled trials was rated with the Physiotherapy Evidence Database scale. For continuous data, we presented the mean difference (D) and 95% confidence interval (CI). Heterogeneity was assessed with I² statistics. The random effects model was applied for the pooled effect estimates. The quality of evidence was assessed using the Grading of Recommendations, Assessment, Development, and Evaluation tool.

Results

The very-low-quality evidence suggested that ESWT was no more effective in decreasing pain than any other conservative treatment (D: –0.8; 95% CI: –3.15, 1.56; P > .5; I² = 85.62%). No significant differences were found between the ESWT and control groups on the pooled Victorian Institute of Sport Assessment-Achilles scores (D: 5.74; 95% CI: –15.02, 26.51; P = .58; I²  = 92.28%), but the quality of evidence was very low.

Conclusion

At present, the quality of the evidence is low; thus, the therapeutic efficacy of ESWT for Achilles tendinopathy is inconclusive.

Introduction

Achilles tendinopathy is among the most prevalent musculoskeletal dysfunctions, accounting for 31% of all lower extremity tendinopathies.¹ The symptoms include pain and edema, function impairment, and stiffness after prolonged rest, and are moderate but persistent.^2,3

In patients with chronic tendinopathy, spontaneous tendon tissue repair is limited,⁴ which causes patients to seek effective therapies. A meta-analysis⁵ demonstrated superiority of any treatment over the wait-and-see strategy. Extracorporeal shockwave therapy (ESWT) appears to be a promising treatment modality in patients with tendinopathies.

According to the concept of evidence-based medicine, recommendations for physiotherapy management are based on reliable external evidence and unambiguous conclusions of meta-analyses, systematic reviews, and randomized clinical trials (RCTs) following high methodological standards. However, meta-analyses have been hampered by a limited number of clinical studies performed to verify ESWT efficacy and different ways of therapeutic efficacy assessment.⁶ The meta-analyses published so far employed a wide range of criteria for primary studies inclusion^{7, 8, 9, 10, 11}; also, the strength of scientific evidence supporting the use of shock wave for Achilles tendinopathy had not been verified by some authors.^10,12

This systematic review aimed to analyze therapeutic procedures for Achilles tendinopathy and interventional recommendations via qualitative assessment and statistical analyses of RCTs results concerning extracorporeal shockwave therapy.

Methods

Research Question

The research question was defined by the PICOS (Participants, Intervention, Comparator, Outcomes, Study Design) format: considering adult patients with Achilles tendinopathy, how effective is shock wave therapy as a monotherapy compared with no intervention or placebo (sham) treatment or any other conservative treatment regarding pain intensity measured using a quantifiable scale (eg, a numeric rating scale or a visual analog scale) and patient-reported outcomes for physical function and disability (eg, Victorian Institute of Sport Assessment-Achilles questionnaire [VISA-A]). The verification was based on selected randomized controlled trials.

Registration

The protocol of this systematic review was registered with the International Platform of Registered Systematic Review and Meta-Analysis Protocols on July 6, 2022 (registration number: INPLASY202270028).¹³ This systematic review and meta-analysis followed the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) 2020 guidelines.¹⁴

Eligibility Criteria

The papers were checked for relevant content and were included based on the inclusion and exclusion criteria defined by the PICOS format (see Supplementary Data). RCT methodological quality and time-point of therapeutic efficacy evaluation (time from therapy completion to follow-up examination) were not considered review inclusion criteria. We included studies with short- (<6 months) and long-term (≥6 months) follow-up.

Information Sources

A search was conducted using the following databases: PubMed, Embase, EBSCOHost, and Ovid. Databases were searched from their inception until the last entry (July 16, 2022). To minimize the risk of omitting relevant sources, the following complementary strategies to explore grey literature were implemented: customized Google search engines, targeted websites, and consultation with clinical experts.¹⁵

Search Strategy

Keywords including “Achilles tendinopathy,” “Achilles tendonitis,” “Achilles tendonopathy,” “shockwave therapy,” “shock wave therapy,” “shock-wave therapy,” “extracorporeal shockwave,” “ESWT,” “treatment,” “intervention,” “therapy,” “management,” and “rehabilitation” were used. The full search strategies for all databases, including any filters and limits used, are presented in the Supplementary Data.

Selection and Data Collection Processes

The selection of studies was conducted in 2 stages. During the first stage, study titles and abstracts were used to select the retrieved articles for further assessment and to eliminate the studies that failed to meet the inclusion criteria. During the second stage, studies that appeared to meet the inclusion criteria were downloaded and the full paper was reviewed. The decision concerning the ultimate inclusion of the study was then made on the basis of the prespecified inclusion and exclusion criteria. Two authors (M.S. and D.C.) independently searched for articles and screened the studies in a blinded manner. Any disagreements between the authors were resolved through consensus, with other research team member (J.M.) acting as arbiter.

Data Items and Study Quality

The following data items were sought: basic publication characteristics (first author, publication year, and country), data on participant characteristics, ESWT intervention (ESWT type, procedure description), outcomes (primary and secondary, method and timing of assessment), and results. Data were independently extracted into tables by 2 investigators (M.S. and D.C.) for each analyzed study. The tables were then compared by the same investigators. If differences were found, the third author (J.M.) searched the full text and corrected the discrepancies.

The methodological quality of randomized clinical studies was determined using the Physiotherapy Evidence Database (PEDro) scale consisting of 10 questions pertaining to the internal validity and statistical information provided.¹⁶ Based on the PEDro score, the methodological quality of trials is rated as high (PEDro scores ≥7), medium (4-6), or low (≤3).⁸ Two reviewers (M.S. and D.C.) independently assessed the methodological quality of the articles included in this meta-analysis. In case of disagreement, the raters discussed the methodological quality together until consensus was reached.

The principles of the GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) approach were applied to assess the quality of the body of evidence.¹⁷ The system offers 4 levels of quality: high, moderate, low, and very low. We used GRADEpro Guideline Development Tool (McMaster University, 2015; developed by Evidence Prime, Inc; available from gradepro.org.) to create the “Summary of Findings” table (Table 1). Also, evidence rating was carried out independently by 2 investigators (M.S. and D.C.) using the GRADEpro. Any disagreements were resolved by consensus, with some input from the third author (J.M.).

Table 1.

Summary of Findings for the Main Comparisons

Certainty Assessment							No. of Patients		Effect
No. of Studies	Study Design	Risk of Bias	Inconsistency	Indirectness	Imprecision	Other Considerations	ESWT	Other Conservative Treatment	Relative (95% CI)	Absolute (95% CI)	Certainty	Importance
VISA-A
2	Randomized trials	Seriousa	Seriousb	Not serious	Seriousc	None	50	50	-	MD 5.74 higher (15.02 lower to 26.51 higher)	⨁○○○ Very low	Critical
NRS
2	Randomized trials	Seriousd	Seriouse	Not serious	Seriousf	None	50	50	-	MD 0.8 lower (3.15 lower to 1.56 higher)	⨁○○○ Very low	Critical

CI, confidence interval; ESWT, extracorporeal shock wave therapy; MD, mean difference; NRS, numeric rating scale; VISA-A, Victorian Institute of Sport Assessment-Achilles questionnaire.

^aSome concern with no blinding of participants and personnel.

^bSignificant heterogeneity was observed (I² = 92.28%, P = .003).

^cSmall sample sizes and wide CIs around estimates of effect.

^dNo blinding of participants and personnel.

^eSignificant heterogenity was observed (I² = 85.62%, P = .008).

^fSmall sample size.

Synthesis Methods

Meta-analysis was undertaken where data (expressed as mean ± standard deviation) were obtained from more than one study assessing the same outcome. Considering the clinical and methodological characteristics of primary studies, a meta-analysis was only possible for those RCTs in which experimental groups with Achilles tendinopathy received ESWT (as a monotherapy) and control participants received some other form of conservative therapy. Quantitative synthesis could be conducted only for the following variables: “load-induced pain” (measured on the numeric rating scale) and “patient's function and activity” (the VISA-A questionnaire).

For continuous data, we presented the mean difference (D) and 95% confidence interval (CI). Heterogeneity was assessed with I² statistics; 25% was considered low, 50% moderate, and 75% high. Statistical significance was set at P < .05. Since high level of clinical and methodological heterogeneity across the study design (ie, different interventions, intervention parameters and outcome measures) was expected, the random effects model was applied for the pooled effect estimates.

Results

Study Selection

A total of 373 articles were identified by the electronic search. Title, abstract and full-text revision revealed that only 6 met the inclusion criteria (Fig 1). The total pooled sample size was 157 participants in the experimental group and 187 participants in the control group.

Fig 1.

PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) 2020 flow diagram.¹⁴

Study Characteristics and Quality Assessment

The included trials were based in the following countries: 3 in Germany,^4,18,19 and 1 each in Denmark,²⁰ Great Britain,²¹ and Italy.²² Table 2 summarizes the methodological quality of randomized clinical trials included in our review. All had been assessed for quality using the PEDro scale; the quality ratings were high^{4,18, 19, 20} or medium.^21,22 Table 3 shows the main characteristics of each intervention.

Table 2.

Randomized Clinical Trials on the Effectiveness of Extracorporeal Shock Wave Therapy for Achilles Tendinopathy Rated With Physiotherapy Evidence Database

Reference	Eligibility Criteria Specified	Participants Randomly Allocated to Groups	Allocation Concealed	Groups Similar at Baseline	Blinding of All Participants	Blinding of All Therapists	Blinding Assessors	>85% Follow-up	Intention-to-Treat Analysis	Between-Group Statistical Comparison	Point and Variability Measures	Scorea
Costa et al21	+	+	+				+	+	–	+	+	6
Lynen et al18	+	+	+	+			+	+	+	+	+	8
Notarnicola et al22	+	+		+						+	+	4
Rasmussen et al20	+	+	+	+	+		+	+	+	+	+	9
Rompe et al4	+	+	+	+			+	+	+	+	+	8
Rompe et al19	+	+	+	+			+	+	+	+	+	8

^aEligibility criteria item is not included in Physiotherapy Evidence Database score calculations.

Table 3.

Summary of Included Studies’ Characteristics

Reference	Groups	Intervention	Outcome Measure	Follow-up
Costa et al21 (Great Britain)	I: ESWT (n = 22) II: placebo (n = 27)	FSWT: 1500 shocks; max 0.2 mJ/mm²; 3 sessions, once a month	VAS; ranges of motion at the ankle joint; calf diameter; tendon diameter; single-leg heel rise; single-leg tiptoe jump; FIL; EuroQol generalized health status questionnaire	3 mo, 1 y
Lynen et al18 (Belgium, Germany)	I: Hyaluronan injections (n = 31) II: ESWT (n = 31)	FSWT: 1500 shocks; 4 Hz; 3 sessions, once a week	VAS; VISA-A; CGI; power Doppler ultrasonography; intensity of clinical parameters	4 wk, 3 and 6 mo
Notarnicola et al22 (Italy)	I: Cold air and high-energy laser therapy (n = 30) II: ESWT (n = 30)	FSWT: 1600 shocks; 0.05-0.07 mJ/mm²; 3 sessions at 3- to 4-d intervals	VAS; Ankle-Hindfoot Scale; Roles and Maudsley Score	Immediately after the end of treatment, 2 and 6 mo
Rasmussen et al20 (Denmark)	I: ESWT (n = 24) II: placebo (n = 24)	RSWT: 2000 shocks; 50 Hz; 12-0.51 mJ/mm²; 4 sessions, once a week	AOFAS score; VAS	4, 8, and 12 wk
Rompe et al4 (Germany)	I: eccentric loading training (n = 25) II: low-energy ESWT (n = 25) III: wait-and-see policy (n = 25)	RSWT: 2000 shocks; 8 Hz; 3 bars; 3 sessions, once a week	VISA-A; general assessment by 6-point Likert scale; 11-point NRS; pain threshold; tenderness; anteroposterior diameter of Achilles tendon of affected and unaffected legs	6 and 16 wk from baseline
Rompe et al19 (Germany)	I: eccentric loading training (n = 25) II: ESWT (n = 25)	RSWT: 2000 shocks; 8 Hz; 2.5 bars; 3 sessions, once a week	VISA-A; general assessment by 6-point Likert scale; 11-point NRS; pain threshold; tenderness at 3 kg assessed on an NRS from 0 to 10	6 and 16 wk from baseline

AOFAS, American Orthopaedic Foot and Ankle Society; CGI, clinical global impression; ESWT, extracorporeal shock wave therapy; FIL, functional index of lower limb activity; FSWT, focused shockwave therapy; NRS, numeric rating scale; RSWT, radial shock wave therapy; VAS, visual analog scale; VISA-A, Victorian Institute of Sport Assessment-Achilles questionnaire.

Results of Individual Studies and Results of Syntheses

The very low-quality evidence (Table 1) suggested that ESWT was no more effective in decreasing pain than any other conservative treatment (D: –0.8; 95% CI: –3.15, 1.56; P > .5) (Fig 2). However, the heterogeneity of the studies included was high (I² = 85.62%, P < .01). No significant differences were found between the ESWT and control groups on the pooled VISA-A scores (D: 5.74; 95% CI: –15.02, 26.51; P = .58, I²  = 92.28%) (Fig 3), but the quality of evidence was very low (Table 1).

Fig 2.

Forest plot of NRS scores. NRS, numeric rating scale.

Fig 3.

Forest plot of VISA-A scores. VISA-A, Victorian Institute of Sports Assessment-Achilles.

Discussion

According to our meta-analysis, pooled estimates for numeric rating scale and VISA-A scores did not differ significantly between the ESWT and control groups. The heterogeneity was quantified as high (I²: 85.62%-92.28%). The quality of the evidence was too low to provide reliable results (Table 1). Therefore, no clear and generalized recommendations can presently be made regarding the efficacy of ESWT monotherapy in patients with Achilles tendinopathy.

Systematic reviews and meta-analyses of randomized trials are considered to provide the most reliable data to guide clinical practice. The meta-analyses conducted so far have assessed the efficacy of radial and focused shockwave therapies in patients with common lower extremity tendinopathies.^{7, 8, 9} Only Punnoose et al,¹² Fan et al,¹⁰ and Paantjens et al¹¹ narrowed down their analysis to patients with Achilles tendinopathy. However, the authors^10,12 did not define the strength of evidence for ESWT efficacy in this lower limb condition, except for Paantjens et al.¹¹ Also, Fan et al¹⁰ failed to carry out separate comparisons between ESWT receivers and those with sham ESWT, traditional nonsurgical treatments, or no treatment. The latter subgroups were collectively analyzed as the control arm. It should be emphasized that, in their practice guide for conducting and reporting narrative reviews, meta-analyses, and meta-syntheses, Siddaway et al²³ strongly recommend the patient, intervention, comparison, outcome (PICO) model. According to this model, the study population, intervention type, control group with another intervention or no intervention, and clinical outcome should be clearly defined.

ESWT can be used as monotherapy or can be combined with other treatment modalities. Different authors used different conservative strategies including physical exercise,^{24, 25, 26, 27, 28} nutritional supplements,²⁹ or standard conservative treatments (pharmacotherapy, activity modification, stretching exercises, and orthosis).³⁰ Rompe et al²⁸ concluded that a combination of eccentric loading and repetitive low-energy shock-wave treatment led to better results than eccentric loading alone.

Literature analysis revealed considerable differences between ESWT application parameters (Table 3); optimal doses and frequency of application for Achilles tendinopathy have not been conclusively determined.⁶ Therapy progress has mainly been evaluated using subjective measures,^{4,20, 21, 22,28,30,31} and, much more rarely, objective assessment^4,18,28 (Table 3). Hence the need to carry out high quality RCTs using assessment tools that objectively verify the efficacy of ESWT for Achilles tendinopathy.

The mechanisms of shock wave action on tendinous tissue are quite complex and still partly speculative.³² ESWT application induces a cascade of cellular and tissue responses,³³ which trigger endogenous physiological tissue repair.³⁴ The positive and beneficial effects of ESWT are associated with stimulation of tenocyte proliferation³⁵ and fibroblast activity.³⁶ Also, increased production of proinflammatory cytokines stimulates collagen synthesis.³⁷ It has also been speculated that shock waves might reactivate tendon healing through micro-disruption of avascular or minimally vascularized tissues,³⁸ resulting in neovascularization, improved blood supply, and stimulation of tissue regeneration.³³ It is believed that postinterventional pain relief results from direct action of ESWT on nerve fibres.³⁹ It was also proposed that ESWT exerted its analgetic effects via inhibitory modulation of nociception (ie, activation of diffuse noxious inhibitory controls⁴⁰ and descending modulation of nociceptive transmission⁴¹).

Limitations

First, our analysis included a small number of studies on ESWT efficacy in patients with Achilles tendinopathy. Second, exclusion of studies published in languages other than English could cause a biased assessment of the topic, as some valuable data from non-English randomized clinical trials might be missing.

Conclusion

Despite high or medium methodological quality of the analyzed RCTs, evidence rating by the GRADE approach was too low to allow conclusions. Hence, no strong recommendations can be made for the use of ESWT in patients with Achilles tendinopathy.

Acknowledgments

The authors thank Agnieszka Perkowska (Jerzy Kukuczka Academy of Physical Education in Katowice, Poland) for providing scientific and language support for this research.

Funding Sources and Conflicts of Interest

No funding sources or conflicts of interest were reported for this study.

Contributorship Information

Concept development (provided idea for the research): M.S.

Design (planned the methods to generate the results): M.S.

Supervision (provided oversight, responsible for organization and implementation, writing of the manuscript): M.S., J.M.

Data collection/processing (responsible for experiments, patient management, organization, or reporting data): M.S., J.M., D.C.

Analysis/interpretation (responsible for statistical analysis, evaluation, and presentation of the results): M.S.

Literature search (performed the literature search): M.S., J.M., D.C.

Writing (responsible for writing a substantive part of the manuscript): M.S.

Critical review (revised manuscript for intellectual content, this does not relate to spelling and grammar checking): J.M., D.C.

Practical Applications.

• •The quality of evidence, which was assessed using the GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) tool, was very low.
• •No definite conclusions on extracorporeal shock wave therapy (as a monotherapy) efficacy for Achilles tendinopathy can be drawn.
• •There is a need for further prospective randomized controlled trials that fulfill the criteria for evidence-based medicine.

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