Long-Term Outcome of Low-Energy Extracorporeal Shock Wave Therapy for Plantar Fasciitis: Comparative Analysis According to Ultrasonographic Findings

Abstract

Objective
To investigate the long-term effect of low-energy extracorporeal shock wave therapy (ESWT) for plantar fasciitis (PF) according to ultrasonography (US) findings.

Methods
Thirty feet of 25 patients with clinical diagnosis of PF were enrolled and divided into two groups (Apparent-US and Uncertain-US) according to US findings, such as plantar fascia thickening or hypoechogenicity. Inclusion criteria were symptom duration >6 months and a fair or poor grade in Roles-Maudsley score (RMS). ESWT (0.10 mJ/mm2, 600 shocks) was given once a week for 6 weeks. Numeric rating scale (NRS) and RMS were evaluated prior to each ESWT session, at short-term follow-up (one week after all ESWT sessions) and long-term follow-up telephone interview (mean 24 months after ESWT). Good and excellent grade in RMS were considered as treatment success.

Results
Repeated measure ANOVA demonstrated that NRS significantly decreased with time after ESWT up to the long-term follow-up (time effect, p<0.001) without group-time interaction (p=0.641), indicating that ESWT equally decreased pain in both groups. Overall success rate was 63.3% (short-term follow-up) and 80.0% (long-term follow-up). In comparative analysis between groups, success rate of Apparent-US and Uncertain-US at short-term follow-up was 61.9% and 66.7%, respectively, and 85.7% and 66.7%, respectively, at long-term follow-up.

Conclusion
If other causes of heel pain are ruled out through meticulous physical examination and ultrasonography, low-energy ESWT in PF seems to be beneficial regardless of US findings. In terms of success rate, however, long-term outcome of Apparent-US appears to be superior to Uncertain-US.

Full text

Long-Term Outcome of Low-Energy
Extracorporeal Shock Wave Therapy for Plantar
Fasciitis: Comparative Analysis According to
Ultrasonographic Findings
Jong-Wan Park, MD1, Kyungjae Yoon, MD, PhD1, Kwang-Soo Chun, MD1,
Joon-Youn Lee, MD1, Hee-Jin Park, MD2, So-Yeon Lee, MD2, Yong-Taek Lee, MD, PhD1
Departments of 1Physical and Rehabilitation Medicine, 2Radiology, Kangbuk Samsung Hospital,
Sungkyunkwan University School of Medicine, Seoul, Korea
Objective To investigate the long-term effect of low-energy extracorporeal shock wave therapy (ESWT) for plantar
fasciitis (PF) according to ultrasonography (US) findings.
Methods Thirty feet of 25 patients with clinical diagnosis of PF were enrolled and divided into two groups
(Apparent-US and Uncertain-US) according to US findings, such as plantar fascia thickening or hypoechogenicity.
Inclusion criteria were symptom duration >6 months and a fair or poor grade in Roles-Maudsley score (RMS).
ESWT (0.10 mJ/mm2, 600 shocks) was given once a week for 6 weeks. Numeric rating scale (NRS) and RMS were
evaluated prior to each ESWT session, at short-term follow-up (one week after all ESWT sessions) and long-term
follow-up telephone interview (mean 24 months after ESWT). Good and excellent grade in RMS were considered
as treatment success.
Results Repeated measure ANOVA demonstrated that NRS significantly decreased with time after ESWT up to
the long-term follow-up (time effect, p<0.001) without group-time interaction (p=0.641), indicating that ESWT
equally decreased pain in both groups. Overall success rate was 63.3% (short-term follow-up) and 80.0% (long-term
follow-up). In comparative analysis between groups, success rate of Apparent-US and Uncertain-US at short-term
follow-up was 61.9% and 66.7%, respectively, and 85.7% and 66.7%, respectively, at long-term follow-up.
Conclusion If other causes of heel pain are ruled out through meticulous physical examination and
ultrasonography, low-energy ESWT in PF seems to be beneficial regardless of US findings. In terms of success rate,
however, long-term outcome of Apparent-US appears to be superior to Uncertain-US.
Keywords Plantar fasciitis, Extracorporeal shock wave therapy (ESWT), Ultrasonography, Treatment outcome
Annals of Rehabilitation Medicine
Original Article
Ann Rehabil Med 2014;38(4):534-540
pISSN: 2234-0645 • eISSN: 2234-0653
http://dx.doi.org/10.5535/arm.2014.38.4.534
Received January 16, 2014; Accepted April 22, 2014
Corresponding author: Yong-Taek Lee
Department of Physical and Rehabilitation Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, 29 Saemunan-ro,
Jongno-gu, Seoul 110-746, Korea
Tel: +82-2-2001-2283, Fax: +82-2-2001-1284, E-mail: yongtaek1.lee@gmail.com
This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/
licenses/by-nc/3.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright © 2014 by Korean Academy of Rehabilitation Medicine

Comparative Analysis According to Ultrasonographic Findings
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INTRODUCTION
Plantar fasciitis (PF) is the most common cause of heel
pain and accounts for 11% to 15% of all foot symptoms
requiring medical care [1-3]. The standard treatments
of PF are conservative measures including insoles, shoe
modification, physical therapy, stretching exercises and
nonsteroidal anti-inflammatory drugs (NSAIDs). Further
approaches include corticosteroid injections [4-8]. For
intractable cases, surgical release of the plantar fascia
may be considered. Extracorporeal shock wave therapy
(ESWT) has been increasingly used as a safe alternative
treatment option for these, since many published papers
have reported a beneficial effect [9-15].
The diagnosis of PF has been typically based on clinical
history and the finding of localized tenderness [14]. Re-
cently, ultrasonography (US) has received increased at-
tention for its diagnostic capabilities, since many studies
have reported the thickening and hypoechoic changes of
the plantar fascia as characteristic features of PF [16-19].
Thus, nowadays diagnosis of PF is often made based on
both clinical and US findings. However, only clinical find-
ings have been used for the diagnosis of PF in the major-
ity of previous outcome studies for ESWT. Based on these
studies, the United States Food and Drug Administration
approved ESWT for the treatment of clinically diagnosed
chronic intractable PF.
To our knowledge, no study has addressed the outcome
of ESWT involving patients with clinically diagnosed PF
but whose US abnormality was uncertain. The present
study was undertaken to investigate the therapeutic effect
of low-energy ESWT in these patients and to compare the
results with clinically diagnosed and US confirmed PF.
MATERIALS AND METHODS
Subjects
Between 2008 and 2013, 70 patients (96 feet) with
chronic refractory PF were enrolled. Diagnosis of PF was
made based on the clinical findings of the patients’ his-
tory and physical examination. As an additional tool, US
evaluation was performed to confirm the PF and rule out
other diseases. Among them, 25 patients (30 feet) met
the inclusion and exclusion criteria. Inclusion criteria
were as follows: PF of at least 6 months in duration, lack
of pain relief by standard treatments including NSAIDs,
insoles, shoe modification, physical therapy and stretch-
ing exercises; completion of the ESWT protocol; grade
of poor or fair in the Roles-Maudsley score (RMS) before
the treatment (Table 1); and availability for long-term (at
least 7 months after ESWT) follow-up telephone inter-
views. Exclusion criteria were history of previous steroid
injections, tarsal tunnel syndrome, polyarthritis and
rheumatic disease, previous surgery of the foot, lumbar
spine disc herniation, trauma and pregnancy. The en-
rolled patients were divided into two groups according to
US findings. Patients who met one of the Korean US diag-
nostic criteria for PF [20] were classified in the Apparent-
US group and those who did not were classified in the
Uncertain-US group (Fig. 1). Korean US diagnostic cri-
teria for PF are plantar fascia thickness >3.8 mm (Fig. 2),
difference of plantar fascia thickness between the symp-
tomatic and asymptomatic foot >1.0 mm and hypoecho-
genicity in plantar fascia (Fig. 3).
Fig. 1. Uncertain ultrasonographic finding that does not
meet any of the Korean ultrasonographic diagnostic cri-
teria for plantar fasciitis as detailed in the text.
Table 1. Roles-Maudsley score
Point Interpretation
Excellent 1 No pain, full movement and activity
Good 2 Occasional discomfort, full movement
and activity
Fair 3 Some discomfort after prolonged activity
Poor 4 Pain-limiting activities

Jong-Wan Park, et al.
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Sonographic evaluation
Two musculoskeletal radiologists evaluated the plantar
fascia of patients using a HDI 5000 (Philips Medical Sys-
tems, Bothell, WA, USA) and LOGIQ E9 (GE Healthcare,
Milwaukee, WI, USA) imaging devices equipped with a
variable frequency linear 6 to 15 MHz probes. Patients
were in prone position during examination with their feet
hanging free over the end of the bed and their ankles dor-
siflexed to 90o. Both sides were evaluated and compared
with each other. Plantar fascia thickness was measured at
its thickest point and echogenicity was assessed around
the medial tubercle of the calcaneus.
ESWT protocol
No local anesthesia was applied. ESWT was performed
using an Evotron electrohydraulic type apparatus (Swi-
Tech Medical AG, Kreuzlingen, Switzerland) by one
musculoskeletal physiatrist. Patients reclined in a prone
position and their ankles were stabilized. The probe was
chosen between EvoTrode R05 (penetration depth, 5−30
mm) and R20 (penetration depth, 25−45 mm) according
to the depth of plantar fascia on US. The point of maximal
heel tenderness was palpated and marked with a skin
marker. US jelly was applied to the heel and low-energy
ESWT (0.10 mJ/mm2, 600 shocks) was given once a week
for 6 weeks. The frequency of shock was 1 Hz. We tried to
distribute the shock waves evenly over the whole of the
tender area by adjustment of the probe.
Clinical assessment
Pain intensity was measured before each ESWT ses-
sion, and at short-term follow-up and long-term follow-
up (telephone interview) using an 11-point pain intensity
numerical rating scale (NRS), where 0 is no pain and 10
is worst possible pain. Short-term follow-up was con-
ducted one week after completion of all ESWT sessions.
Subsequently, long-term follow-up telephone interview
was performed a mean of 24 months after ESWT (range,
7−42 months). RMS was also assessed before the first
treatment, and at short-term and long-term follow-ups
(Table 1). Overall success rate and success rate of each
study group were calculated at short-term and long-term
follow-ups. We defined a RMS grade of good or excellent
as treatment success.
Statistical analyses
Independent t-test and repeated measure ANOVA test to
compare and analyze the effect of low-energy ESWT be-
tween apparent-US and uncertain-US groups. The relation-
ship among plantar fascia thickness, age, symptom duration
and pain scores (NRS) were evaluated using Pearson cor-
relation coefficient. All analyses were performed with the
SPSS ver. 18.0 (SPSS Inc., Chicago, IL, USA). A p-value <0.05
was considered statistically significant.
Fig. 2. Apparent ultrasonographic abnormal finding
shows a plantar fascia thickness >3.8 mm.
Fig. 3. Apparent ultrasonographic abnormal finding
shows hypoechogenicity in the plantar fascia.

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RESULTS
Table 2 shows baseline characteristics. All variables
were not significantly different between Apparent-US and
Uncertain-US group, except plantar fascia thickness. The
results of repeated measure ANOVA test demonstrated
that the subjective pain was significantly decreased with
time up to long-term follow-up (mean 24 months after
ESWT) (time effect, p<0.001). However, there was no sig-
nificant group-time interaction (p=0.641 for interaction),
which means ESWT equally decreased subjective pain in
both groups (Fig. 4). The pain score at short-term follow-
up (one week after completion of all ESWT sessions) and
long-term follow-up did not show significant difference
between the two groups. These findings also indicated
that there was no significant difference in the effect of
lower-energy ESWT between two groups. In our study,
overall success rate of ESWT was 63.3% at the short-term
follow-up and 80.0% at the long-term follow-up. In inter-
group comparison, success rates at short-term follow-up
were similar between Apparent-US (61.9%) and Uncer-
tain-US (66.7%). At the long-term follow-up, those were
85.7% and 66.7%, respectively (Table 3). There was no
significant correlation between plantar fascia thickness
on US, age, pain scores at each assessment and symptom
duration.
DISCUSSION
Subjective pain started to decrease from 1 week after
first treatment session and continued to improve with
time up to mean 24 months. Using our definition of suc-
cess, overall success rate at short-term follow-up (one
week after completion of all ESWT sessions) and long-
term follow-up (mean 24 months after ESWT) was 63.3%
and 80.0%, respectively. These results are comparable
to previous reports that most patients improve within
2 weeks [21] and symptoms continued to improve with
time to 6 months [22]. These findings are also consistent
with other randomized control trials [10,11,23,24] and a
previous study that reported long-term symptom relief
after ESWT [25].
US is often used for the diagnosis of PF by direct mea-
surement of the thickness and observing echogenicity
of the plantar fascia. Several studies [16-18,26-29] have
consistently demonstrated a marked increase in plantar
Table 2. Basic characteristics according to ultrasonographic findings
Variable Apparent-US (n=21) Uncertain-US (n=9) Total (n=30) p-valuea)
Sex (male:female) 3:18 4:5 7:23
Lesion side (right:left) 8:13 4:5 12:18
Age (yr) 0.220
Mean (SD) 52.7 (9.8) 47.3 (12.6) 51.1 (10.8)
Range 25−72 21−61 21−72
Symptom duration (mo) 0.281
Mean (SD) 19.8 (13.8) 13.9 (12.7) 18.0 (13.6)
Range 6−36 6−48 6−48
Plantar fascia thickness (mm) <0.001
Mean (SD) 4.4 (0.8) 3.0 (0.6) 4.0 (0.1)
Range 3.5−6.1 2.0−3.7 2.0−6.1
Initial NRS 0.614
Mean (SD) 6.1 (2.3) 6.6 (2.4) 6.3 (2.3)
Initial RMS (poor:fair) 16:5 6:3 22:8
Follow-up (mo) 0.500
Mean (SD) 24.5 (10.8) 21.4 (12.6) 23.6 (11.2)
Range 7−41 7−42 7−42
Apparent-US, apparent ultrasonographic abnormal group; Uncertain-US, uncertain ultrasonographic group; SD, stan-
dard deviation; NRS, numeric rating scale; RMS, Roles-Maudsley score.
a)Independent samples t-test.

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fascia thickness in symptomatic feet compared to as-
ymptomatic sides. As a general rule, increased thickness
(>4 mm) and decreased echogenicity of plantar fascia
are considered as consistent US findings in PF [28,29]. In
Korean, Yoon et al. [20] reported that increased thickness
(>3.8 mm), difference of thickness between symptomatic
and asymptomatic sides (>1.0 mm) and hypoechogenici-
ty of plantar fascia were clinically meaningful US findings
of PF. In the present study, we used these Korean criteria
as the reference value for the determination of Apparent-
US and Uncertain-US.
Repeated measure ANOVA revealed no significant
group-time interaction (p=0.641 for interaction). In addi-
tion, the pain scores at short-term and long-term follow-
ups did not show a significant difference between the
study groups. These findings suggest that ESWT equally
improve subjective pain in both study groups regardless
of presence or absence of apparent abnormalities on US,
which are consistent with prior finding that plantar fascia
thickness does not influence the outcome of ESWT [25].
However, the present results are contrary to the common
understanding that plantar fascia thickness influences
treatment outcomes [14]. Plantar fascia thickness can be
marked increased in PF [17,18] and substantially reduced
after ESWT, showing a correlation with pain reduction
[30,31].
Several considerations about the main problem with
US may to some extent explain such conflicting results.
Operator-dependent technique and factors, such as lack
of standardization of measurement points or machine
settings, may affect the measured thickness value and
appearance of plantar fascia, and make it difficult to de-
termine reference values for designation of Apparent-
US or Uncertain-US [32]. Indeed, large differences in
the mean plantar fascia thickness were measured in the
previous studies, in which the mean values varied from
2.9−8.1 mm in patients with PF. Ranges of plantar fascia
thickness in patients with PF were 3.2−6.8 mm in one
study [26] and 4.3−8.1 mm in another [27]. Yet another
study reported a mean plantar fascia thickness of 2.9 mm
in patients with unilateral heel pain [17]. Additionally, US
evaluation of hypoechoic changes in the plantar fascia
Fig. 4. Repeated measure ANOVA test demonstrates that
pain score decreases with time up to long-term follow-
up (mean 24 months after ESWT) (time effect, p<0.001)
without significant group-time interaction (p=0.641 for
interaction). The pain scores at short-term follow-up
(one week after completion of all ESWT sessions) and
long-term follow-up do not show significant difference
between the study groups. ESWT, extracorporeal shock
wave therapy; NRS, numeric rating scale; Apparent-US,
apparent ultrasonographic abnormal group; Uncertain-
US, uncertain ultrasonographic group.
Table 3. Success rate at short-term and long-term follow-ups according to ultrasonographic findings
Follow-up Apparent-US (n=21) Uncertain-US (n=9) Total (n=30)
Short-term
Success rate (%) 61.9 66.7 63.3
Excellent 1 0 1
Good 12 6 18
Long-term
Success rate (%) 85.7 66.7 80.0
Excellent 3 1 4
Good 15 5 20
Apparent-US, apparent ultrasonographic abnormal group; Uncertain-US, uncertain ultrasonographic group.

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was reported to display surprisingly low agreement [33],
which could be attributed to the fact that the definition
of echogenicity is dependent on the adjacent muscle,
but there is no adjacent muscle for comparison when
examining the plantar fascia with US. For these limita-
tions, variations may exist among US examinations of the
plantar fascia. Thus, proper and careful interpretation of
findings is necessary when using US in routine clinical
practice. Nevertheless, US is important to rule out other
causes of heel pain or to establish the diagnosis of PF.
One limitation of the present study is the small number
of patients studied. In addition, it has been reported that
body mass index [34], walking hours per day, diabetes
mellitus, and documented psychological disorder affect
treatment outcome [25], but we did not consider these
factors since this information was not available.
In conclusion, if other causes of heel pain are ruled out
and diagnosis of PF is established through meticulous
physical examination and US, low-energy ESWT appears
to be beneficial regardless of US finding. In terms of suc-
cess rate, however, long-term outcome of patients with
apparent US abnormalities in plantar fascia appears to be
superior to those with uncertain US findings.
CONFLICT OF INTEREST
No potential conflict of interest relevant to this article
was reported.
ACKNOWLEDGMENTS
The authors thank Ms. Miyeon Lee, Medical Informa-
tion Library in Kangbuk Samsung Hospital for her advice
about statistical analyses used in the study.
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