The long- and short-term effect of radial extracorporeal shockwave therapy on pain level in patients with plantar fasciosis – preliminary research

Introduction

Plantar fasciitis (PF) is a common condition characterized by pain typically located at the inferomedial aspect of the heel, and which limits everyday activities related to locomotion. The term fasciitis suggests the presence of inflammation; however, this is not supported by histopathological findings, which are more indicative of a degenerative process, i.e. fasciosis [1-3]. Recent studies report that PF may negatively affect postural control and gait, resulting in reduced step length, width and velocity [4-6]. Poor postural control may also result in an increased risk of falls [7]. Chronic pain in the plantar aspect of the heel adversely affects not only foot health and function, but also the overall quality of life (QoL) by limiting physical activity and full participation in social activities. Studies conducted with the use of the Foot Health Status Questionnaire indicate that PF has an adverse impact on QoL, with a more pronounced decrease noted in women than in men [8,9]. The widespread occurrence of PF and the growing awareness of its negative impact on quality of life highlight the need to identify the more effective therapies and dosages that can facilitate efficient and rapid treatment.
The literature indicates an increased prevalence of PF in women over 45 years of age, with overweight and obesity constituting additional risk factors. A body mass index (BMI) above 30 kg/m2 increases the risk of PF five-fold in comparison with normal BMI [10]. Other reported risk factors include pes planus and a limited plantar flexion. PF may also result from frequent running on hard surfaces, physical exercises that overburden the lower limbs, and occupations that require long periods standing [11,12].
The most common physiotherapeutic treatment options of PF include the use of ultrasound waves, manual therapy, low-level laser therapy, and the more widely-available shockwave therapy [13,14]. A recent alternative is high-energy laser therapy (HIL), which, according to a meta-analysis conducted by de la Barra Ortiz et al., may provide pain reduction and improvement in quality of life (QoL) lasting for at least three months [15]. Another option is radial extracorporeal shockwave therapy (r-ESWT), which meta-analyses indicate may also be effective in PF patients, although further studies are required to evaluate its durability [16-18]. The goal of the present study was to determine the short- and long-term effects of r-ESWT on pain reduction in a group of patients with chronic PF.

Materials and methods

Design
The trial was performed as a single blinded study. It was conducted as a preliminary research as part of an ongoing parallel group three-arm trial. The research was carried out in accordance with the ethical standards of the Helsinki Declaration. The study protocol was registered on The Australian New Zealand Clinical Trials Registry (ANZCTR) (registration number: ACTRN12622001510730; date of registration 2022-12-05) and approved by the Bioethics Committee of the Medical University of Warsaw (KB/30/2018). All patients provided their written informed consent for participation.
Participants
The sample size was calculated using G*Power software version 3.1.9.7 (University of Kiel, Kiel, Germany) [19]. An a priori power analysis for F tests, ANOVA: Repeated measures, within factors was conducted. Assuming a 5% level of significance, 90% power of six measures in one group, with a medium effect size of 0.25 expressed as Cohen’s f (obtained through eta-partial square value), a total sample size of 24 was determined [20]. Assuming a 15% dropout rate, a sample size of 28 was estimated.
Consecutive participants diagnosed with PF were recruited from the Department of Rehabilitation of the University Clinical Center. The diagnosis of PF was based on physical examination findings and imaging data: X-ray, computed tomography, or magnetic resonance imaging [21].
The eligibility criteria for participants included age over 18 years and PF-related pain. Exclusion criteria included the following: oncological diseases, ongoing anticoagulant therapy, pregnancy, pacemaker, advanced lower limb deformities, lower limb length asymmetry exceeding 2 cm, and any PF treatment within six months prior to examination.
Intervention
All patients underwent five sessions of r-ESWT at five to seven-day intervals. Each session included 2000 shocks (10 Hz, 2,5 Ba) directed at the plantar side of the heel. The shocks were applied with continuous movements of a 15mm transmitter head, including a 5 s pause at the trigger points. The procedure was conducted in a prone position, with the ankle joint supported by a half roller. The treatment used a BTL-5000 SWT Power + High Intensity Laser 12 W (BTL, Warsaw, Poland).
Outcome measures
The outcome measure for the study was pain assessment conducted with the use of Visual Analogue Scale (VAS) and Numerical Rating Scale (NRS) to measure pain intensity, and the Laitinen Pain Questionnaire (LPQ) to evaluate the multidimensional impact of pain on the patient. The assessment was performed at six consecutive timepoints: at each treatment session (points 1-5) and at a six-month follow-up (point 6).
The VAS consists of a 10 cm line with the phrases “no pain” and “worst pain imaginable” marked at the start and end. The NRS consists of a horizontal line with 11 points, marked from 0 to 10, and anchored at both ends by descriptions of pain level. The VAS and NRS were presented separately [22-24].
The LPQ is composed of five separate questions regarding pain intensity, pain frequency, frequency of use of painkillers and limitation of activity. Responses to questions are given using a Likert scale scored from 0 to 4, with an additional explanation next to each number, where 0 indicates no problem and 4 a severe problem [25,26].
Statistical analysis
Prior to the analysis, no missing values or outliers were identified. Differences between the parameters at the six consecutive time points were analyzed using Friedman repeated measures analysis of variance by ranks (χ2), followed by a mean-ranks post hoc test, as required. The effect size was calculated using Kendall’s coefficient of concordance (W). Correlations between parameters were assessed using Spearman’s rank correlation coefficient (ρ). A statistical significance level of 0.05 was considered for all hypothesis tests. The statistical analysis was conducted using Statistica PL version 13.3 (TIBCO Software Inc., Palo Alto, CA, USA).

Results

All 28 participants completed the study; the flow of patients through each stage is presented in Figure 1. The majority were women. The mean age of the study group was 54 years, with the youngest patient being 37, and the oldest 71. All patients exhibited either overweight or obesity. The detailed characteristics of the group are presented in Table 1.
Fig.1. The flow of patient groups through each stage of the trial
Tab.1. Baseline demographics
A statistically significant decrease in pain intensity was observed after therapy, and after the six-month follow-up, compared to baseline (p < 0.001; Table 2). Most of the analyzed patients experienced satisfactory long-term pain reduction, with the majority reducing their pain by 50% or more; one patient achieved a pain reduction of 49%, while four experiences a reduction lower than 10%.
Significant reductions in perceived pain were not noted at every time point; however, while the differences between adjacent time points were not found to be statistically significant, post hoc testing identified significant differences between non-contiguous points. The post hoc comparisons revealed substantial differences between following time-points: VAS: 1 vs 4, 1 vs 5, 1 vs 6, 2 vs 6, 3 vs 6; NRS: 1 vs 3, 1 vs 4, 1 vs 5, 1 vs 6, 2 vs 4, 2 vs 5, 2 vs 6, 3 vs 6; LPQ: 1 vs 2, 1 vs 3, 1 vs 4, 1 vs 5, 1 vs 6, 2 vs 6, 3 vs 6, 4 vs 6; Neither age, height, weight, nor BMI correlated with the pain level in the studied group. No side effects or injury were observed as a result of therapy.
Tab. 2. Pain severity outcomes at six consecutive time points

Discussion

Although the efficacy of ESWT in treating plantar fasciosis (PF) has been frequently reported, there is still a lack of findings based on longer follow-up periods. This study aimed to fill this gap not only by reporting the long-term effects of r-ESWT on pain, but also by providing detailed observations of gradual changes over five-week therapy with a comprehensive treatment protocol.
Most patients with PF seek medical help due to pain that worsens over time and affects multiple aspects of daily life. The present study achieved a significant and satisfactory reduction in pain severity for the majority of patients in the group. The characteristics of the study group align with data from the United States [10]. In addition, the treatment effects were sustained during the six-month follow-up, providing valuable information for planning rehabilitation procedures in everyday clinical practice. Eslamian et al. [27] compared the effect of Corticosteroid Injection (CSI) and r-ESWT on pain in patients not responding to NSAID nor physiotherapy. Over half of patients treated with r-ESWT (55%–60%) achieved a pain reduction on VAS scale that met the criterion set by the authors, whereas CSI therapy proved less effective (35%-40%); similar VAS-pain improvement results were noticed by Hocaoğlu et al. [28] in a comparison of ESWT and CSI. These observed reductions in pain [27] [28] are in line with those of the present study. As this noticeable difference between shockwaves and corticosteroids may result from the lack of inflammation in chronic PF, Lemont et al. [1] suggest a reevaluation of treatment options.
The effect of rESWT is also influenced by the methodology of the performed procedure, the parameters selected by the physiotherapist, and the planning of the interval length between therapeutic sessions. The present study used parameters and intervals recommended by the manufacturers, and which are commonly used by physiotherapists in everyday clinical practice. Knowing the exact effects of therapy between sessions may enable better prediction of therapeutic outcomes and possible adjustments or modifications of therapy at its early stage. Further research comparing various treatment parameters with both constant and progressive dosing will allow better matching of the therapy to the patient's needs.
Several studies have made observations in these directions. A randomized single-blind study by Narin et al. [29] compared two different rESWT regimens in 41 patients. Both groups received 10 rESWT sessions each. In one group, rESWT was applied at 3.0 bars of pressure and a frequency of 15 Hz, whereas the other group received treatment at a pressure of 2.0 bars and a frequency of 10 Hz. The follow-up period lasted 12 weeks after treatment completion. During that time, a considerable reduction in pain VAS scores was observed in both groups, with no significant difference between them.
Szajkowski et al. [30] compared progressive dosing with a control group where parameters were not changed during the treatment period. The authors increased the intensity of the shocks and decreased the frequency every two subsequent treatment sessions, starting from 2.5 bars and 14 Hz at the first session and ending with a dose of 5 bars and 10 Hz at the sixth session. The control group received shocks with an intensity of 3 bars and a frequency of 12 Hz. Systematic reductions in pain were noted after treatment and after a one-month follow-up, with the experimental group, i.e. with progressive dosing, demonstrating a greater reduction in pain intensity on the VAS scale. In a study of patients with knee osteoarthritis, Zhang et al. [31] compared the effects of three different static dosages with a placebo group. While a statistically significant difference was noted between experimental groups and the placebo group, no differences were observed between the 2000 and 4000 shock treatments; however, the higher density led to greater pain reduction indicated by VAS.
While the treatment process was found to positively impact the health of patients in both our study and those mentioned above, pain reduction was achieved using different parameters and methodologies. Therefore, we emphasize the need for further research on the dosage and regimen for RSWT treatment.
Limitations
The main limitation is the lack of a placebo control group; however, for ethical reasons, it was problematic to involve a symptomatic control group that would not receive treatment for such a long period. Another limitation is the lack of objective methods for measuring improvement that could be used in the follow-up visits; these could include ultrasound to compare differences in soft tissue structure, pedobarography to assess patient balance and weight distribution between the lower limbs, or digital gait analysis for comprehensive assessment of gait phases.

Conclusions

RSWT can be an effective tool in rehabilitation of patients with PF. It appears to provide clinically meaningful improvement in pain symptoms in most qualified patients during short- and long-term observation, despite no reduction in body weight over the follow-up period. Although no significant improvement was noted during the five-week rehabilitation cycle with RSWT, this does not necessarily indicate that improvement will not occur after the conclusion of treatment. In our opinion, further studies are needed on the dosage and effects of RSWT during therapy in a larger group of patients.

Funding

This research did not receive any external funding.

Conflict of interest

There authors declare no conflicts of interest.

References