Accepted Manuscript Title: Intrinsic foot muscle volume in experienced runners with and without chronic plantar fasciitis Author: R.T.H. Cheung L.K.Y. Sze N.W. Mok G.Y.F. Ng PII: DOI: Reference:
S1440-2440(15)00225-X http://dx.doi.org/doi:10.1016/j.jsams.2015.11.004 JSAMS 1244
To appear in:
Journal of Science and Medicine in Sport
Received date: Revised date: Accepted date:
6-3-2015 27-10-2015 14-11-2015
Please cite this article as: Cheung RTH, Sze LKY, Mok NW, Ng GYF, Intrinsic foot muscle volume in experienced runners with and without chronic plantar fasciitis, Journal of Science and Medicine in Sport (2015), http://dx.doi.org/10.1016/j.jsams.2015.11.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Intrinsic foot muscle volume in experienced runners with and without chronic plantar
2
fasciitis
3
Cheung R.T.H.1; Sze L.K.Y.2; Mok N.W.1; Ng G.Y.F.1
4
1
5
Kong
6
2
ip t
1
cr
Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hong
us
Industrial Centre, The Hong Kong Polytechnic University, Hong Kong
an
7
Corresponding author: Dr. Roy T.H. Cheung, ST511, Department of Rehabilitation
9
Sciences, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong. Email: [email protected]; Phone: +852 2766 6739; Fax: +852 2330 8656
d
10
M
8
te
11
Word count (excluding abstract and references): 1,563
13
Abstract word count: 229
14
Number of tables: 1
15
Number of figures: 0
Ac ce p
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Page 1 of 15
16
Intrinsic foot muscle volume in experienced runners with and without chronic plantar
17
fasciitis
ip t
18
Abstract
20
Objectives: Plantar fasciitis, a common injury in runners, has been speculated to be
21
associated with weakness of the intrinsic foot muscles. A recent study reported that
22
atrophy of the intrinsic forefoot muscles might contribute to plantar fasciitis by
23
destabilizing the medial longitudinal arch. However, intrinsic foot muscle volume
24
difference between individuals with plantar fasciitis and healthy counterparts remains
25
unknown. This study examined the relationship of intrinsic foot muscle volume and
26
incidence of plantar fasciitis.
27
Design: Case-control study
28
Methods: 20 experienced (>=5 years) runners were recruited. Ten of them had bilateral
29
chronic (>=2 years) plantar fasciitis while the others were healthy characteristics-
30
matched runners. Intrinsic muscle volumes of the participants’ right foot were scanned
31
with a 1.5 T magnetic resonance system and segmented using established methods.
32
Body-mass normalized intrinsic foot muscle volumes were compared between runners
33
with and without chronic plantar fasciitis.
34
Results: There was significant greater rearfoot intrinsic muscle volume in healthy
35
runners than runners with chronic plantar fasciitis (Cohen’s d=1.13; p=0.023). A similar
36
trend was also observed in the total intrinsic foot muscle volume but it did not reach a
Ac ce p
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M
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us
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19
Page 2 of 15
statistical significance (Cohen’s d=0.92; p=0.056). Forefoot volume was similar between
38
runners with and without plantar fasciitis.
39
Conclusions: These results suggest that atrophy of intrinsic foot muscles may be
40
associated with symptoms of plantar fasciitis in runners. These findings may provide
41
useful information in rehabilitation strategies of chronic plantar fasciitis.
cr
ip t
37
Keywords: Anatomy; Lower extremity; Running; MRI research
an
43
us
42
44
Introduction
M
45
Distance running is a popular sport. The growing running population can be partially
47
reflected by the rapid growth in the number of finishers in the world marathon majors1.
48
Such running bloom can be partly explained by its positive health impact in terms of
49
cardiovascular fitness improvement and stress reduction2,3. However, running-related
50
overuse injury is also very common. A series of studies have reported that 39-85% of
51
runners would incur at least a single injury during a given year4–6. In a retrospective
52
study of 2,002 runners, plantar fasciitis (PF) was found to be the third most common
53
running-related overuse injury with an incidence of 7.9%7 and the economic burden of
54
PF in the United States was up to $376 million in 20078.
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55
Despite the substantial encumbrance and medical cost of PF, its injury mechanism
56
and etiology remain speculative. Many contributing factors, including weakness of the
57
intrinsic foot muscles (IFM)9, have been associated with the development of PF. It has
Page 3 of 15
been speculated that weak IFM provides insufficient dynamic truss support to the
59
medial longitudinal arch, causing increased strain on the plantar fascia. Clinically,
60
strengthening exercise of the IFM is a major component in PF rehabilitation10,11.
61
However, there is a lack of direct comparison of IFM strength between individuals with
62
and without PF in today’s literature. Such information may provide the theoretical
63
justification for using strengthening exercise for patients with PF.
cr
ip t
58
Clinically, it is difficult to accurately measure IFM strength12. It has been shown that
65
muscle volume measurement using MRI is strongly correlated with strength13,14 and
66
performance15 in young and elderly individuals. The fact that MRI possesses excellent
67
spatial resolution, it is very suitable for measuring the size of IFM thus indirectly quantify
68
its strength. A recent MRI study16 that examined subjects with chronic unilateral PF has
69
reported a 5.2% reduction of IFM volume in the forefoot than the side without pain, while
70
the rearfoot and total IFM volumes were similar. However, the shortcoming of that study
71
is it compared the healthy foot with the painful foot in subjects with unilateral PF. The
72
pain in one leg might have altered the gait pattern of the subject thus the functional
73
demand of the IFM. Without a healthy control group, the IFM volume difference between
74
individuals with PF and healthy individuals remains unknown.
Ac ce p
te
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M
an
us
64
75
Hence, this study examined the total, rearfoot, and forefoot volume of IFM in
76
experienced runners with and without bilateral chronic PF. We hypothesized that
77
healthy runners would have greater body-mass normalized IFM volume than those with
78
PF.
79
Page 4 of 15
80
Methods Twenty experienced (>=5 years) runners were recruited in this study. Ten of them
82
(five males and five females) had never incurred any running-related overuse injury and
83
another 10 of them (five males and five females) had bilateral chronic PF (>=2 years).
84
Self-reported instruments including Foot and Ankle Ability Measure (FAAM) and Lower
85
Extremity Functional Scale (LEFS) score were used to measure the level of symptoms
86
in runners with PF. FAAM is a self-administered questionnaire containing 32 questions
87
in 5-point Likert scale. A higher FAAM score represents a higher functional level of an
88
individual. LEFS has 20 items each scored on 0-4 Likert scale and the overall score
89
ranges from 0 to 80, where higher score indicating better functional ability. The
90
institutional review board reviewed and approved the research protocol and all of the
91
participants provided their written informed consent before being tested.
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MRI images of the right foot were taken with a 1.5 T magnetic resonance system.
93
Participants were positioned supine on the table with the ankle positioned at 45 of
94
plantarflexion and other joints well stabilized by cushions. T1 weighted images of the
95
entire length of the foot were acquired perpendicularly to the plantar aspect of the foot
96
using a spin-echo sequence (repetition time=500 ms; echo time=16 ms; averages=3;
97
slice thickness=4 mm; gap=0 mm; field of view=120x120 mm; flip angle=90;
98
matrix=512x512). We calculated the IFM volume according to a previous study16. In
99
brief, IFM were segmented with the Mimics version 16 (Materialise, Leuven, Belgium)
100
by excluding all non-contractile tissues such as bone, fat, connective tissue, nerve, and
101
blood vessels. Volumes were then computed by summing the product of slice thickness
102
and the muscle cross-sectional area for each image. In order to minimize the effects of
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Page 5 of 15
different body built between participants, the foot muscle volume was normalized by
104
body mass. Similar to Chang et al.16, rearfoot and forefoot segments were defined by
105
splitting the total number of images containing muscle into posterior half and anterior
106
half, respectively. The inter-session reliability of this imaging processing method was
107
examined in a previous study and the coefficient of variance for IFM and EFM were
108
1.3% and 1.7% respectively16.
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Between-group differences in the participants’ demographics were assessed by
110
independent t-tests. Total and regional normalized IFM volumes were compared
111
between healthy and PF group using independent t-tests. Global alpha was set at 0.05
112
and all the statistical tests were performed using PASW for Windows (version 18, SPSS
113
software, Chicago, IL, USA). In addition, in order to avoid overreliance on statistical
114
tests17, the effect size, in terms of Cohen’s d, was calculated using PASS (version 13,
115
NCSS Statistical Software, Kaysville, UT, USA).
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Results
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The means and standard deviations of participants’ age, body height, body mass,
119
weekly mileage, and usual pacing in the healthy and PF groups are shown in Table 1.
120
FAAM and LESF scores in the PF group are also presented in Table 1. The two groups
121
were comparable in their demographic data, running intensity, and pace. Total mean
122
normalized IFM volume in the healthy and PF group were 2,083.3±258.70 mm3/kg and
123
1,838.0±277.08 mm3/kg, respectively. There was a trend of statistical difference in the
124
IFM volume between the two groups (p=0.056) and its effect size was 0.92. We
Page 6 of 15
observed a significant difference in the rearfoot IFM volume between the two groups
126
(healthy: 942.5±208.02 mm3/kg; PF: 746.8±129.18 mm3/kg; p=0.023; Cohen’s d=1.13).
127
Conversely, the forefoot volume between two groups were similar (healthy:
128
1,140.8±149.48 mm3/kg; PF: 1,091.2±169.51 mm3/kg; p=0.496; Cohen’s d=0.31).
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Discussion
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This study recruited characteristics-matched runners with and without chronic
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bilateral PF and we found a significant difference in the rearfoot muscle volumes
133
between the two groups. These findings were in divergence to the data reported by
134
Chang et al.16.
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First, in comparison to the data by Chang et al., our IFM volume was much larger
136
(un-normalized IFM volume=135,583 mm3 and 117,514 mm3 in healthy runners and
137
runners with PF in our study vs. 113,300 mm3 and 108,000 mm3 in Chang et al.). This
138
discrepancy is likely due to the difference in the sample nature. In our study, we enlisted
139
experienced runners who had regular physical training. In contrast, Chang et al.
140
recruited patients with PF from medical clinics and other public sources. It is not
141
surprising that the active adults are presenting larger muscle volume, including IFM. We
142
did not compare our findings with other previous studies, because of the differences in
143
the image processing method18 and targeted structure19,20.
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Second, Chang et al.16 enrolled subjects with unilateral PF and they used the
145
subjects’ healthy foot as their own control. Such study design has not considered the
146
potential asymmetry between the two legs21, which may partially explain the
Page 7 of 15
discrepancy between their findings with ours. More importantly, our study observed a
148
difference in the rearfoot IFM instead of forefoot IFM. Since some of the forefoot
149
intrinsic muscles, such as interossei muscles, do not provide direct mechanical support
150
to the medical longitudinal arch, rearfoot muscle strength may therefore be the focus of
151
rehabilitation in the strengthening exercise protocol. However, IFM atrophy could be an
152
adaptation of pain or a secondary change due to PF. Without any prospective data, the
153
treatment rationale of IFM strengthening, which is a standard care of PF22, remains
154
putative.
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Since the annual injury rate in regular runners was up to 85%4–6, the participants in
156
our control group, who were experienced runners (>=5 years) with no previous running-
157
related overuse injury, could be reasonably considered as healthy counterparts for
158
comparison. All participants in the PF group suffered from chronic bilateral PF. We did
159
not recruit runners with unilateral PF, as it may be inappropriate to classify the
160
asymptomatic foot as healthy foot.
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Several limitations should be addressed in light of the findings presented. First, we
162
only analyzed the total and regional IFM volumes in this study. In view the contribution
163
of individual muscles to the foot arch support is not uniform23, we recommend future
164
study to examine the size of individual muscles in subjects with and without PF and
165
even include the investigation of extrinsic foot muscle volume. Second, this study is a
166
cross-sectional study and it did not provide any causal relationship between IFM volume
167
or strength and the incidence of PF. Future prospective study is therefore warranted to
168
examine the contribution of IFM weakness in the development of PF and the
169
effectiveness of strengthening program in runners with PF.
Page 8 of 15
170 171
Conclusion In summary, runners with chronic PF presented smaller IFM volumes in the rearfoot
173
region than their healthy counterparts. This finding indicates IFM strengthening exercise
174
may be effective to manage PF, although prospective data is needed for further
175
justification.
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Practical implications
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Runners with chronic plantar fasciitis have smaller intrinsic foot muscle volume than
181 182 183 184
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Strengthening of the intrinsic foot muscle may be a potential treatment for runners with plantar fasciitis.
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their healthy counterparts.
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Our findings were based on regional analysis of intrinsic foot muscle volume, instead of individual muscle volume comparison.
185
Acknowledgements
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This study was funded by Department of Rehabilitation Sciences, The Hong Kong
187
Polytechnic University (G-UB42). The authors acknowledge the Department of
188
Radiology & Imaging, Queen Elizabeth Hospital for the MRI scanning and technical
Page 9 of 15
189
support. We also thank the contribution from Ms. Ying Li, Mr. Lloyd Chan, Mr. Yat-
190
Fai Cheng, Mr. Samuel Li, and Mr. Sam Chan.
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References
192
1 Official
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World
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https://worldmarathonmajors.com/. Accessed Aug 26, 2015.
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2 Williams Paul T. Lower prevalence of hypertension, hypercholesterolemia, and
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diabetes in marathoners. Med Sci Sports Exerc 2009; 41(3):523–529. Doi:
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10.1249/MSS.0b013e31818c1752.
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3 Williams Paul T. Reduction in incident stroke risk with vigorous physical activity:
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evidence from 7.7-year follow-up of the national runners’ health study. Stroke J Cereb
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Circ 2009; 40(5):1921–1923. Doi: 10.1161/STROKEAHA.108.535427.
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4 Bovens AM, Janssen GM, Vermeer HG, et al. Occurrence of running injuries in adults
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following a supervised training program. Int J Sports Med 1989; 10 Suppl 3:S186–
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5 Watson MD, DiMartino PP. Incidence of injuries in high school track and field athletes and its relation to performance ability. Am J Sports Med 1987; 15(3):251–254.
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6 van Gent RN, Siem D, van Middelkoop M, et al. Incidence and determinants of lower
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Med 2007; 41(8):469–480; discussion 480. Doi: 10.1136/bjsm.2006.033548.
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7 Taunton JE, Ryan MB, Clement DB, et al. A retrospective case-control analysis of 2002 running injuries. Br J Sports Med 2002; 36(2):95–101. 8 Tong Kuo Bianchini, Furia John. Economic burden of plantar fasciitis treatment in the United States. Am J Orthop Belle Mead NJ 2010; 39(5):227–231. 9 Warren BL, Jones CJ. Predicting plantar fasciitis in runners. Med Sci Sports Exerc 1987; 19(1):71–73. Doi: 2881184.
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Karagounis Panagiotis, Tsironi Maria, Prionas George, et al. Treatment of plantar
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fasciitis in recreational athletes: two different therapeutic protocols. Foot Ankle Spec
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2011; 4(4):226–234. Doi: 10.1177/1938640011407320.
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Young CC, Rutherford DS, Niedfeldt MW. Treatment of plantar fasciitis. Am Fam
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Physician 2001; 63(3):467–474, 477–478. 12
Soysa Achini, Hiller Claire, Refshauge Kathryn, et al. Importance and challenges
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of measuring intrinsic foot muscle strength. J Foot Ankle Res 2012; 5(1):29. Doi:
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10.1186/1757-1146-5-29. 13
Akagi Ryota, Takai Yohei, Ohta Megumi, et al. Muscle volume compared to
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cross-sectional area is more appropriate for evaluating muscle strength in young and
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elderly individuals. Age Ageing 2009; 38(5):564–569. Doi: 10.1093/ageing/afp122. 14
Meakin Judith R, Fulford Jonathan, Seymour Richard, et al. The relationship
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between sagittal curvature and extensor muscle volume in the lumbar spine. J Anat
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2013; 222(6):608–614. Doi: 10.1111/joa.12047. 15
Akagi Ryota, Tohdoh Yukihiro, Hirayama Kuniaki, et al. Relationship of pectoralis
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major muscle size with bench press and bench throw performances. J Strength Cond
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Res 2014; 28(6):1778–1782. Doi: 10.1519/JSC.0000000000000306.
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Chang Ryan, Kent-Braun Jane A, Hamill Joseph. Use of MRI for volume
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estimation of tibialis posterior and plantar intrinsic foot muscles in healthy and chronic
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plantar fasciitis limbs. Clin Biomech Bristol Avon 2012; 27(5):500–505. Doi:
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10.1016/j.clinbiomech.2011.11.007.
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Nuzzo Regina. Scientific method: statistical errors. Nature 2014; 506(7487):150–
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Andersen Henning, Gjerstad Michaela D, Jakobsen Johannes. Atrophy of foot
muscles: a measure of diabetic neuropathy. Diabetes Care 2004; 27(10):2382–2385. 19
Yu JS, Spigos D, Tomczak R. Foot pain after a plantar fasciotomy: an MR
analysis to determine potential causes. J Comput Assist Tomogr 1999; 23(5):707–
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712. 20
Chundru Usha, Liebeskind Amy, Seidelmann Frank, et al. Plantar fasciitis and
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calcaneal spur formation are associated with abductor digiti minimi atrophy on MRI of
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the foot. Skeletal Radiol 2008; 37(6):505–510. Doi: 10.1007/s00256-008-0455-2. 21
Tate Christine Marie, Williams Glenn N, Barrance Peter J, et al. Lower extremity
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muscle morphology in young athletes: an MRI-based analysis. Med Sci Sports Exerc
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2006; 38(1):122–128.
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Warren BL. Plantar fasciitis in runners. Treatment and prevention. Sports Med
1990; 10(5):338–345. 23
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McKeon Patrick O, Hertel Jay, Bramble Dennis, et al. The foot core system: a
new paradigm for understanding intrinsic foot muscle function. Br J Sports Med 2015;
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49(5):290. Doi: 10.1136/bjsports-2013-092690.
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Table legend:
254
Table 1. Demographic characteristics of participants.
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Page 14 of 15
255
Table 1. Demographic characteristics of participants
Healthy group
Age, year
32.6 (5.44)
34.5 (4.99)
Body height, m
1.67 (0.09)
Body mass, kg
63.80 (14.82)
64.90 (7.00)
0.834
Weekly mileage, km/week
29.7 (8.59)
30.0 (18.26)
0.963
Usual pacing, min/km
5.90 (1.29)
5.40 (0.84)
0.318
258
cr us
an
M
77.3 (12.2)
Not applicable
0.291
Data were presented as mean (standard deviation)
Ac ce p
257
Not applicable
0.427
te
Foot and Ankle Ability Measure 256
1.71 (0.06)
72.2 (10.8)
d
Lower Extremity Functional scale
p
ip t
Plantar fasciitis group
Page 15 of 15
S1440-2440(15)00225-X http://dx.doi.org/doi:10.1016/j.jsams.2015.11.004 JSAMS 1244
To appear in:
Journal of Science and Medicine in Sport
Received date: Revised date: Accepted date:
6-3-2015 27-10-2015 14-11-2015
Please cite this article as: Cheung RTH, Sze LKY, Mok NW, Ng GYF, Intrinsic foot muscle volume in experienced runners with and without chronic plantar fasciitis, Journal of Science and Medicine in Sport (2015), http://dx.doi.org/10.1016/j.jsams.2015.11.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Intrinsic foot muscle volume in experienced runners with and without chronic plantar
2
fasciitis
3
Cheung R.T.H.1; Sze L.K.Y.2; Mok N.W.1; Ng G.Y.F.1
4
1
5
Kong
6
2
ip t
1
cr
Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hong
us
Industrial Centre, The Hong Kong Polytechnic University, Hong Kong
an
7
Corresponding author: Dr. Roy T.H. Cheung, ST511, Department of Rehabilitation
9
Sciences, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong. Email: [email protected]; Phone: +852 2766 6739; Fax: +852 2330 8656
d
10
M
8
te
11
Word count (excluding abstract and references): 1,563
13
Abstract word count: 229
14
Number of tables: 1
15
Number of figures: 0
Ac ce p
12
16
Page 1 of 15
16
Intrinsic foot muscle volume in experienced runners with and without chronic plantar
17
fasciitis
ip t
18
Abstract
20
Objectives: Plantar fasciitis, a common injury in runners, has been speculated to be
21
associated with weakness of the intrinsic foot muscles. A recent study reported that
22
atrophy of the intrinsic forefoot muscles might contribute to plantar fasciitis by
23
destabilizing the medial longitudinal arch. However, intrinsic foot muscle volume
24
difference between individuals with plantar fasciitis and healthy counterparts remains
25
unknown. This study examined the relationship of intrinsic foot muscle volume and
26
incidence of plantar fasciitis.
27
Design: Case-control study
28
Methods: 20 experienced (>=5 years) runners were recruited. Ten of them had bilateral
29
chronic (>=2 years) plantar fasciitis while the others were healthy characteristics-
30
matched runners. Intrinsic muscle volumes of the participants’ right foot were scanned
31
with a 1.5 T magnetic resonance system and segmented using established methods.
32
Body-mass normalized intrinsic foot muscle volumes were compared between runners
33
with and without chronic plantar fasciitis.
34
Results: There was significant greater rearfoot intrinsic muscle volume in healthy
35
runners than runners with chronic plantar fasciitis (Cohen’s d=1.13; p=0.023). A similar
36
trend was also observed in the total intrinsic foot muscle volume but it did not reach a
Ac ce p
te
d
M
an
us
cr
19
Page 2 of 15
statistical significance (Cohen’s d=0.92; p=0.056). Forefoot volume was similar between
38
runners with and without plantar fasciitis.
39
Conclusions: These results suggest that atrophy of intrinsic foot muscles may be
40
associated with symptoms of plantar fasciitis in runners. These findings may provide
41
useful information in rehabilitation strategies of chronic plantar fasciitis.
cr
ip t
37
Keywords: Anatomy; Lower extremity; Running; MRI research
an
43
us
42
44
Introduction
M
45
Distance running is a popular sport. The growing running population can be partially
47
reflected by the rapid growth in the number of finishers in the world marathon majors1.
48
Such running bloom can be partly explained by its positive health impact in terms of
49
cardiovascular fitness improvement and stress reduction2,3. However, running-related
50
overuse injury is also very common. A series of studies have reported that 39-85% of
51
runners would incur at least a single injury during a given year4–6. In a retrospective
52
study of 2,002 runners, plantar fasciitis (PF) was found to be the third most common
53
running-related overuse injury with an incidence of 7.9%7 and the economic burden of
54
PF in the United States was up to $376 million in 20078.
Ac ce p
te
d
46
55
Despite the substantial encumbrance and medical cost of PF, its injury mechanism
56
and etiology remain speculative. Many contributing factors, including weakness of the
57
intrinsic foot muscles (IFM)9, have been associated with the development of PF. It has
Page 3 of 15
been speculated that weak IFM provides insufficient dynamic truss support to the
59
medial longitudinal arch, causing increased strain on the plantar fascia. Clinically,
60
strengthening exercise of the IFM is a major component in PF rehabilitation10,11.
61
However, there is a lack of direct comparison of IFM strength between individuals with
62
and without PF in today’s literature. Such information may provide the theoretical
63
justification for using strengthening exercise for patients with PF.
cr
ip t
58
Clinically, it is difficult to accurately measure IFM strength12. It has been shown that
65
muscle volume measurement using MRI is strongly correlated with strength13,14 and
66
performance15 in young and elderly individuals. The fact that MRI possesses excellent
67
spatial resolution, it is very suitable for measuring the size of IFM thus indirectly quantify
68
its strength. A recent MRI study16 that examined subjects with chronic unilateral PF has
69
reported a 5.2% reduction of IFM volume in the forefoot than the side without pain, while
70
the rearfoot and total IFM volumes were similar. However, the shortcoming of that study
71
is it compared the healthy foot with the painful foot in subjects with unilateral PF. The
72
pain in one leg might have altered the gait pattern of the subject thus the functional
73
demand of the IFM. Without a healthy control group, the IFM volume difference between
74
individuals with PF and healthy individuals remains unknown.
Ac ce p
te
d
M
an
us
64
75
Hence, this study examined the total, rearfoot, and forefoot volume of IFM in
76
experienced runners with and without bilateral chronic PF. We hypothesized that
77
healthy runners would have greater body-mass normalized IFM volume than those with
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PF.
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Methods Twenty experienced (>=5 years) runners were recruited in this study. Ten of them
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(five males and five females) had never incurred any running-related overuse injury and
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another 10 of them (five males and five females) had bilateral chronic PF (>=2 years).
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Self-reported instruments including Foot and Ankle Ability Measure (FAAM) and Lower
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Extremity Functional Scale (LEFS) score were used to measure the level of symptoms
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in runners with PF. FAAM is a self-administered questionnaire containing 32 questions
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in 5-point Likert scale. A higher FAAM score represents a higher functional level of an
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individual. LEFS has 20 items each scored on 0-4 Likert scale and the overall score
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ranges from 0 to 80, where higher score indicating better functional ability. The
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institutional review board reviewed and approved the research protocol and all of the
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participants provided their written informed consent before being tested.
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MRI images of the right foot were taken with a 1.5 T magnetic resonance system.
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Participants were positioned supine on the table with the ankle positioned at 45 of
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plantarflexion and other joints well stabilized by cushions. T1 weighted images of the
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entire length of the foot were acquired perpendicularly to the plantar aspect of the foot
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using a spin-echo sequence (repetition time=500 ms; echo time=16 ms; averages=3;
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slice thickness=4 mm; gap=0 mm; field of view=120x120 mm; flip angle=90;
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matrix=512x512). We calculated the IFM volume according to a previous study16. In
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brief, IFM were segmented with the Mimics version 16 (Materialise, Leuven, Belgium)
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by excluding all non-contractile tissues such as bone, fat, connective tissue, nerve, and
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blood vessels. Volumes were then computed by summing the product of slice thickness
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and the muscle cross-sectional area for each image. In order to minimize the effects of
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different body built between participants, the foot muscle volume was normalized by
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body mass. Similar to Chang et al.16, rearfoot and forefoot segments were defined by
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splitting the total number of images containing muscle into posterior half and anterior
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half, respectively. The inter-session reliability of this imaging processing method was
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examined in a previous study and the coefficient of variance for IFM and EFM were
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1.3% and 1.7% respectively16.
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Between-group differences in the participants’ demographics were assessed by
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independent t-tests. Total and regional normalized IFM volumes were compared
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between healthy and PF group using independent t-tests. Global alpha was set at 0.05
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and all the statistical tests were performed using PASW for Windows (version 18, SPSS
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software, Chicago, IL, USA). In addition, in order to avoid overreliance on statistical
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tests17, the effect size, in terms of Cohen’s d, was calculated using PASS (version 13,
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NCSS Statistical Software, Kaysville, UT, USA).
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Results
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The means and standard deviations of participants’ age, body height, body mass,
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weekly mileage, and usual pacing in the healthy and PF groups are shown in Table 1.
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FAAM and LESF scores in the PF group are also presented in Table 1. The two groups
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were comparable in their demographic data, running intensity, and pace. Total mean
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normalized IFM volume in the healthy and PF group were 2,083.3±258.70 mm3/kg and
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1,838.0±277.08 mm3/kg, respectively. There was a trend of statistical difference in the
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IFM volume between the two groups (p=0.056) and its effect size was 0.92. We
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observed a significant difference in the rearfoot IFM volume between the two groups
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(healthy: 942.5±208.02 mm3/kg; PF: 746.8±129.18 mm3/kg; p=0.023; Cohen’s d=1.13).
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Conversely, the forefoot volume between two groups were similar (healthy:
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1,140.8±149.48 mm3/kg; PF: 1,091.2±169.51 mm3/kg; p=0.496; Cohen’s d=0.31).
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Discussion
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This study recruited characteristics-matched runners with and without chronic
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bilateral PF and we found a significant difference in the rearfoot muscle volumes
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between the two groups. These findings were in divergence to the data reported by
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Chang et al.16.
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First, in comparison to the data by Chang et al., our IFM volume was much larger
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(un-normalized IFM volume=135,583 mm3 and 117,514 mm3 in healthy runners and
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runners with PF in our study vs. 113,300 mm3 and 108,000 mm3 in Chang et al.). This
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discrepancy is likely due to the difference in the sample nature. In our study, we enlisted
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experienced runners who had regular physical training. In contrast, Chang et al.
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recruited patients with PF from medical clinics and other public sources. It is not
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surprising that the active adults are presenting larger muscle volume, including IFM. We
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did not compare our findings with other previous studies, because of the differences in
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the image processing method18 and targeted structure19,20.
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Second, Chang et al.16 enrolled subjects with unilateral PF and they used the
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subjects’ healthy foot as their own control. Such study design has not considered the
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potential asymmetry between the two legs21, which may partially explain the
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discrepancy between their findings with ours. More importantly, our study observed a
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difference in the rearfoot IFM instead of forefoot IFM. Since some of the forefoot
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intrinsic muscles, such as interossei muscles, do not provide direct mechanical support
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to the medical longitudinal arch, rearfoot muscle strength may therefore be the focus of
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rehabilitation in the strengthening exercise protocol. However, IFM atrophy could be an
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adaptation of pain or a secondary change due to PF. Without any prospective data, the
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treatment rationale of IFM strengthening, which is a standard care of PF22, remains
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putative.
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Since the annual injury rate in regular runners was up to 85%4–6, the participants in
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our control group, who were experienced runners (>=5 years) with no previous running-
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related overuse injury, could be reasonably considered as healthy counterparts for
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comparison. All participants in the PF group suffered from chronic bilateral PF. We did
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not recruit runners with unilateral PF, as it may be inappropriate to classify the
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asymptomatic foot as healthy foot.
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Several limitations should be addressed in light of the findings presented. First, we
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only analyzed the total and regional IFM volumes in this study. In view the contribution
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of individual muscles to the foot arch support is not uniform23, we recommend future
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study to examine the size of individual muscles in subjects with and without PF and
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even include the investigation of extrinsic foot muscle volume. Second, this study is a
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cross-sectional study and it did not provide any causal relationship between IFM volume
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or strength and the incidence of PF. Future prospective study is therefore warranted to
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examine the contribution of IFM weakness in the development of PF and the
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effectiveness of strengthening program in runners with PF.
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Conclusion In summary, runners with chronic PF presented smaller IFM volumes in the rearfoot
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region than their healthy counterparts. This finding indicates IFM strengthening exercise
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may be effective to manage PF, although prospective data is needed for further
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justification.
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Practical implications
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Runners with chronic plantar fasciitis have smaller intrinsic foot muscle volume than
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Strengthening of the intrinsic foot muscle may be a potential treatment for runners with plantar fasciitis.
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their healthy counterparts.
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Our findings were based on regional analysis of intrinsic foot muscle volume, instead of individual muscle volume comparison.
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Acknowledgements
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This study was funded by Department of Rehabilitation Sciences, The Hong Kong
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Polytechnic University (G-UB42). The authors acknowledge the Department of
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Radiology & Imaging, Queen Elizabeth Hospital for the MRI scanning and technical
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support. We also thank the contribution from Ms. Ying Li, Mr. Lloyd Chan, Mr. Yat-
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Fai Cheng, Mr. Samuel Li, and Mr. Sam Chan.
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Table legend:
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Table 1. Demographic characteristics of participants.
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Table 1. Demographic characteristics of participants
Healthy group
Age, year
32.6 (5.44)
34.5 (4.99)
Body height, m
1.67 (0.09)
Body mass, kg
63.80 (14.82)
64.90 (7.00)
0.834
Weekly mileage, km/week
29.7 (8.59)
30.0 (18.26)
0.963
Usual pacing, min/km
5.90 (1.29)
5.40 (0.84)
0.318
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77.3 (12.2)
Not applicable
0.291
Data were presented as mean (standard deviation)
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Not applicable
0.427
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Foot and Ankle Ability Measure 256
1.71 (0.06)
72.2 (10.8)
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Lower Extremity Functional scale
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Plantar fasciitis group
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