Effectiveness of low energy extracorporeal shock wave therapy in the treatment of chronic insertional Achilles tendinopathy

Chronic Achilles tendinopathy (AT) is a prevalent overuse injury of the foot and ankle, marked by pain, swelling, and impaired performance. It is commonly classified into mid-portion AT (mid-AT) and insertional AT (ins-AT), with mid-AT being more common (55–65%) than ins-AT (20–25%) [1]. AT is most frequently observed between ages 40–59 and is particularly prevalent among runners and other athletes [2, 3].

Conservative treatments for ins-AT include rest, nonsteroidal anti-inflammatory drugs, footwear modifications, stretching, eccentric strengthening, and corticosteroid injections. However, these approaches often yield suboptimal results in chronic cases. Extracorporeal shockwave therapy (ESWT) has emerged as a promising non-invasive alternative [4]. While its exact mechanisms remain incompletely understood, ESWT may promote tendon healing through mechanotransduction, neovascularization, modulation of nociceptor activity, and tissue remodeling [5, 6].

ESWT is often used after failure of first-line conservative management and may be more effective when integrated with structured loading programmes [6-8]. Several systematic reviews and meta-analyses have supported its use in chronic Achilles tendinopathy, although the magnitude of effect appears to vary by protocol and patient selection [5, 7, 8].

However, some recent high-quality studies have questioned its benefits. Mansur et al. [9] and Pinitkwamdee et al. [10] conducted double-blind randomised controlled trials and found no significant additional effect of ESWT over eccentric training or sham therapy in chronic ins-AT, particularly in older adults.

Given this controversy, further research was warranted to clarify ESWT’s role. The current study aimed to evaluate the effectiveness of low-energy ESWT in managing chronic insertional Achilles tendinopathy.

This quasi-experimental study was conducted in the Department of Physical Medicine and Rehabilitation, Chittagong Medical College Hospital, Chattogram, Bangladesh, from October 19, 2021 to April 18, 2022. Eligible participants were men or women aged 18-60 years with chronic ins-AT for at least 3 months, morning pain VAS score >5, history of failed conservative treatment, and willingness to participate. Failed conservative treatment was defined as persistent symptoms despite at least one standard non-operative modality such as activity modification, anti-inflammatory medication, therapeutic exercise, or physioltherapy before enrolment.

This was a consecutive, feasibility-based hospital study. Instead of a formal sample size calculation, all eligible patients presenting during the predefined study period were enrolled using a consecutive sampling approach, resulting in a final sample of 39 participants. This approach was chosen to maximise data capture in an exploratory setting where prior estimates required for sample size calculation were limited. However, the study may be underpowered to detect small-to-moderate associations.

Outpatients of Physical Medicine and Rehabilitation were evaluated through history, physical examination, and relevant investigations. These included complete blood count, C-reactive protein, rheumatoid factor, serum uric acid, serum thyroid-stimulating hormone, fasting blood glucose, 2-hour postprandial blood glucose, plain X-ray (anteroposterior and lateral views of the involved calcaneus), and ultrasonography of the affected heel. Exclusion criteria were previous Achilles tendon rupture or surgery, inflammatory arthritis, acute infection, uncontrolled diabetes mellitus, severe neurologic deficit affecting the limb, pregnancy, bleeding disorder or anticoagulant use, local corticosteroid injection within the previous 3 months, current systemic corticosteroid therapy, and unwillingness to complete follow-up.

Face-to-face interviews were conducted using a semi-structured questionnaire to collect socio-demographic data, clinical history, previous treatment details, and baseline scores of the visual analogue scale (VAS; 0=no pain, 10=worst imaginable pain) and Roles and Maudsley score (RMS; 1=excellent, 2=good, 3=fair, 4=poor). Past treatment and investigation records were verified through patient reports and available documents.

Treatment was carried out using low-energy ESWT with an Enraf-Nonius Endopuls 811 device. A 15 mm radial probe was applied over the most tender point at the Achilles tendon insertion using ultrasound gel, with the patient in prone position. Shockwaves were delivered tangentially in a lateral-to-medial direction while the ankle was gently mobilized in all planes to target the entire tendon insertion and surrounding tissue.

Each patient received 4 weekly ESWT sessions (4 Hz frequency, 0.06 mJ/mm² energy flux density, 800 pulses/session). Participants were advised not to start any additional tendon-directed intervention during the treatment period; specifically, no corticosteroid injection or oral steroid was prescribed as co-intervention. Outcomes were assessed using VAS and RMS at 1, 2, and 3 months after treatment. Data were recorded in a pretested questionnaire and analyzed statistically.

Collected data were compiled in Microsoft Excel and analysed using SPSS version 28. Categorical variables were presented as frequencies and percentages, while continuous variables were expressed as mean (standard deviation) (SD). Repeated-measures analysis of variance (ANOVA) was used to compare mean VAS and RMS values across time, followed by Bonferroni-adjusted post hoc pairwise comparisons (baseline versus 1, 2, and 3 months; 1 versus 2 months; 1 versus 3 months; and 2 versus 3 months). A two-sided P<0.05 was considered statistically significant.

To ensure data quality, a detailed work manual was prepared and the questionnaire was pretested for clarity and completeness. Data collection, analysis, and report writing were conducted under supervision of the study guide. Because the study was single-arm and exploratory, internal validity was strengthened by restricting enrolment to patients with chronic symptoms who had not improved with prior conservative treatment and by using repeated within-patient assessment at prespecified follow-up points.

Ins-AT is difficult to treat once symptoms become chronic, because mechanical overload, degenerative tendon change, and persistent pain sensitisation may coexist at the tendon-bone junction. In that setting, ESWT is attractive because it is non-invasive and can be delivered after failure of routine conservative care. The present study therefore focused on a clinically relevant subgroup: patients with chronic ins-AT who had remained symptomatic despite prior non-operative treatment.

The absence of a control group is the main limitation of this study and restricts causal inference. We attempted to reduce this threat by enrolling only patients with persistent symptoms after failed conservative treatment, then following the same individuals prospectively at fixed intervals after a standardised ESWT protocol. Although spontaneous improvement cannot be excluded, this design makes simple regression to the mean a less satisfactory explanation for the consistent stepwise improvement observed across repeated assessments.

The observed reduction in pain and improvement in function are biologically plausible. ESWT is thought to act through a combination of pain modulation, stimulation of local circulation, and promotion of tissue remodeling [5, 6]. Clinically, this may translate into gradual pain reduction over weeks rather than an immediate effect, which matches the temporal pattern seen in this cohort, with progressive improvement from month 1 through month 3.

Our findings are broadly consistent with prior case-series and some controlled studies reporting benefit of ESWT in chronic Achilles tendinopathy [7, 11]. At the same time, more recent randomised trials have shown mixed results, especially when ESWT is compared against active loading programmes or sham procedures [9, 10, 12]. This inconsistency likely reflects heterogeneity in energy level, number of sessions, chronicity, baseline severity, and whether ESWT was used alone or as an adjunct to eccentric loading.

These findings have practical implications for rehabilitation services in resource-constrained settings. In patients who do not respond to usual conservative measures, low-energy ESWT may offer a non-surgical option that can be delivered in an outpatient department with short-term follow-up. However, the present results should be interpreted as supportive rather than definitive evidence, because the study cannot determine whether ESWT is superior to continued exercise-based care, sham therapy, or natural recovery.

Strengths of the study include the clearly defined patient group, use of validated outcome measures, standardized treatment protocol, and complete short-term follow-up. The single-centre design, feasibility-based sample, and 3-month follow-up limit external validity and do not address durability of response. In addition, eccentric loading was not delivered as a structured co-intervention, which may have influenced the magnitude of response relative to some comparative trials [7, 9].

Overall, the study supports the short-term clinical usefulness of ESWT in chronic insertional Achilles tendinopathy after failed conservative treatment, while also highlighting the need for controlled studies with longer follow-up and clearer comparison against established loading-based interventions. Low-energy ESWT was associated with short-term improvement in pain and function in patients with chronic insertional Achilles tendinopathy, particularly among those who had not improved with prior conservative treatment.

Conclusion

Low-energy ESWT was associated with short-term improvement in pain and function in chronic insertional Achilles tendinopathy, particularly among patients who had not improved with prior conservative treatment.