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ORIGINAL ARTICLES
Plantar Pressures in Children With and Without
Sever’s Disease
Ricardo Becerro de Bengoa Vallejo, DPM, PhD*
Marta Elena Losa Iglesias, PhD†
David Rodrı
´guez Sanz, BS‡
Juan Carlos Prados Frutos, MD, PhD§
Paloma Salvadores Fuentes, PhD†
Jose
´Lo
´pez Chicharro, MD, PhD*
Background: A case-control study was conducted to compare static plantar pressures
and distribution of body weight across the two lower limbs, as well as the prevalence of
gastrocnemius soleus equinus, in children with and without calcaneal apophysitis
(Sever’s disease).
Methods: The participants were 54 boys enrolled in a soccer academy, of which eight
were lost to follow-up. Twenty-two boys with unilateral Sever’s disease comprised the
Sever’s disease group and 24 healthy boys constituted a control group. Plantar pressure
data were collected using pedobarography, and gastrocnemius soleus equinus was
assessed.
Results: Peak pressure and percentage of body weight supported were significantly
higher in the symptomatic feet of the Sever’s disease group than in the asymptomatic
feet of the Sever’s disease group and the control group. Every child in the Sever’s
disease group had bilateral gastrocnemius equinus, while nearly all children in the
control group had no equinus.
Conclusions: High plantar foot pressures are associated with Sever’s disease, although
it is unclear whether they are a predisposing factor or a result of the condition.
Gastrocnemius equinus may be a predisposing factor for Sever’s disease. Further
research is needed to identify other factors involved in the disease and to better
understand the factors that contribute to abnormal distribution of body weight in the
lower limbs. (J Am Podiatr Med Assoc 101(1): 17-24, 2011)
Apophysitis, or inflammation of an apophysis, is
caused by microavulsions at the bone-cartilage
junction
1
resulting from repetitive motion and
overuse during periods of rapid growth. Calcaneal
apophysitis was first described in 1912 by Sever
2
and later given the name ‘‘Sever’s disease.’’ The
calcaneal apophysis is a cartilaginous growth center
onto which the Achilles tendon inserts.
3, 4
Kvist and
Heinonen
5
and Kim et al
6
refined the definition of
Sever’s disease to indicate a traction epiphysitis. It
is most commonly associated with sports that
involve running and jumping.
7-9
In a retrospective
study of 20 children with Sever’s disease, McKenzie
et al
10
found that all of the children participated in
such sports, mainly in track and field events and
soccer.
Sever’s disease has been reported to be the most
common cause of heel pain in athletic children.
8, 11
Orava and Puranen
12
and Orava and Virtanen
13
found that it comprises 16.3% and 22.7% of exertion
injuries in children, respectively. The heel pain
limits physical activity and may interfere with
*Escuela Universitaria Enfermeria, Fisioterapia y Podologia,
Facultad de Medicina, Universidad Complutense de Madrid,
Madrid, Spain.
†Facultad de Ciencias de la Salud, Universidad Rey Juan
Carlos, Madrid, Spain.
‡Soccer Club Atle
´tico de Madrid, Madrid, Spain.
§Facultad de Medicina, Universidad Complutense de Madrid,
Madrid, Spain.
Corresponding author: Ricardo Becerro de Bengoa
Vallejo, DPM, PhD, Escuela Universitaria Enfermeria, Fisio-
terapia y Podologia, Facultad de Medicina, Universidad
Complutense de Madrid, Avenida Complutense s/n, Madrid,
28040 Spain. (E-mail: ribebeva@enf.ucm.es)
Journal of the American Podiatric Medical Association Vol 101 No 1 January/February 2011 17
activities of daily living. The condition is self-
limiting because the calcaneal cartilage disappears,
at about age 14 years in girls and 16 years in boys, to
allow for complete calcaneal ossification.
5
The
etiology of Sever’s disease is controversial,
14
and
proposed contributing factors include participation
in high-impact sports, improper footwear, running
on hard surfaces, and excessive pressures on the
plantar heel.
15
The condition is associated with
radiographic changes such as variations in the
normal ossification pattern.
8
Cessation of the high-
impact activity and thus reducing mechanical
overload at the affected heel is a standard compo-
nent of treatment.
16-18
We sought to investigate the relationship between
mechanical heel overload and development of
Sever’s disease by measuring static plantar pres-
sures of young athletes with and without Sever’s
disease. We also sought to determine the distribu-
tion of body weight between the two limbs and to
investigate its association with Sever’s disease. The
association between gastrocnemius soleus equinus
and Sever’s disease was also evaluated because of
the relationship found between gastrocnemius
soleus equinus and Achilles tendon thickening.
19
The calcaneal apophysis is a cartilaginous growth
center onto which the Achilles tendon inserts.
3, 4, 20
Haglund
21
titled his article ‘‘Concerning Some Rare
but Important Surgical Injuries Brought on by
Violent Exercise,’’ but he provided no justification
of how violent the exercise was. Many au-
thors
2, 5, 10, 12, 18, 22-27
have noted anecdotally that
affected children were active and vigorous and that
symptoms often presented at the beginning of the
sporting season and while the child was undergoing
a growth spurt. However, none of these studies
measured or reported the children’s actual activity
levels or provided evidence of growth spurts.
The plantar fascia originates from the medial
tubercle on the plantar aspect of the calcaneus, near
the attachment of the Achilles tendon to the
calcaneus, a secondary bony growth center, or the
epiphysis.
7, 28-30
Proximal to the epiphysis is the
apophysis, where the Achilles tendon actually
inserts. The apophysis has its own slower-growing
growth plate, separate from the physeal plate.
3, 4
The calcaneal growth plate and the apophysis are
situated in an area subject to high stress from the
plantar fascia and Achilles tendon
31
and may be
affected by increased tension on the calcaneus.
The main theory in the literature on the patho-
genesis of Sever’s disease is that it is an overuse
syndrome from repetitive microtrauma from in-
creased traction on the apophysis. This increased
traction is believed to be initiated by running and
jumping, which causes avulsion fractures on a tiny
scale followed by inflammation.
8, 20, 32-36
Because of
the rapid proliferation of cells in growth plates, the
apophysis is thought to be more susceptible to
injury.
37
Liberson et al
31
examined calcaneal apoph-
yses histologically and with computed tomography
and found fibrous bands in the cartilage perpendic-
ular to os calcis. This finding indicated powerful
stresses in the remodeling process, leading Liberson
et al
31
to suggest a traction-stress argument, where
pain is thought to occur when remodeling exceeds
certain rates.
The theory that tight triceps surae cause exces-
sive tension through the Achilles tendon, increasing
the traction on the apophysis, has been a commonly
cited mechanical factor in much of the litera-
ture.
1, 7, 8, 17-19, 32, 37-44
Studies
8, 18, 19, 32
that looked
at patients with Sever’s disease generally involved
assessment by multiple raters of foot dorsiflexion
on the leg, thereby reducing uniformity of measure-
ment and reliability of results. This omission calls
into question the existence of excessive tightness in
the triceps surae at all. No studies have compared
whether symptomatic patients are tighter in the
triceps surae than their asymptomatic counter-
parts.
45
References to biomechanical influences in Sever’s
disease are scattered throughout the literature.
However, neither prospective systematic measure-
ment of the feet of those identified with Sever’s
disease nor comparison to an asymptomatic popu-
lation has been performed.
45
Krantz
32
observed
limited ankle dorsiflexion and postulated traumatic
inflammation to the apophysis. McKenzie et al
10
noted, retrospectively, that 95% of their Sever’s
disease patients had a biomechanical imbalance
that produced a whipping action in the Achilles
tendon, increasing the stress on the apophysis.
However, this theory has no supportive evidence.
Szames et al
19
found that of 79 children with Sever’s
disease, 65 (82.3%) tested positive for ankle equinus
owing to Achilles tendon tightness and concluded
that equinus may predispose a child to Sever’s
disease.
The exact mechanism by which equinus may
influence Sever’s disease is unknown.
46
In a
retrospective study, we also found a relationship
between equinus and Sever’s disease. This strong
relationship between the calcaneal apophysitis and
equinus could explain why treating heel lift and
limiting strenuous activity seem to relieve symp-
toms. A child with Sever’s disease usually reports
nonradiating pain in the posterior calcaneus with
18 January/February 2011 Vol 101 No 1 Journal of the American Podiatric Medical Association
weightbearing activities, which is relieved by rest.
The pain is usually accompanied by tight triceps
surae, resulting in a reduction of dorsiflexion to 108
or less.
2, 8, 11, 14, 17-19
One possible cause of the pain
is the tension on the Achilles tendon due to
shortening of the gastrocnemius soleus complex
and production of excessive traction force on the
apophysis.
47
Patients and Methods
Participants
Participants in this study were boys enrolled in a
soccer school who presented for a final health
screening of the season. The study protocol
conformed to the guidelines set forth in the
Declaration of Helsinki, and written parental con-
sent for the evaluation was obtained. All of the boys
spent the same amount of time participating in their
sport, including after-school and weekend training
and competition. The exclusion criterion was a
recent history of ankle injury, including sprain,
tendinitis, or any pathology other than Sever’s
disease. None of the participants had a neurologic
condition affecting the lower extremity.
The soccer school enrolled 215 children aged 8 to
15 years. Fifty-four boys were selected randomly
from individuals who presented to the study, of
which eight were lost to follow-up (two with and six
without Sever’s disease). Thus, 46 boys completed
the study. They were divided into two groups: 1)
those who had been diagnosed (by a podiatrist
[R.B.B.V.] affiliated with the study) with unilateral
Sever’s disease between September 2006 and
August 2007, and 2) those who were healthy, who
served as the control group. The asymptomatic foot
of each child in the Sever’s disease group was also
used as a control. No child had been diagnosed with
bilateral Sever’s disease or had bilateral heel pain.
For diagnostic purposes, Sever’s disease was
defined as pain on mediolateral compression of
the calcaneus in the area of the growth plate.
48
The
pain had to be of at least 2 months’ duration and
coincide with physical activity, as well as be severe
enough to sufficiently interfere with normal physi-
cal activity such as walking.
11
All of the children
were symptomatic when they presented to the
clinic.
The characteristics of the boys in the Sever’s
disease and control groups are given in Table 1. All
of the children were in the ‘‘healthy weight’’
category as defined by the Centers for Disease
Control and Prevention,
49
from the 5th percentile to
the 85th percentile, except for one 11-year-old boy
in the Sever’s disease group who was underweight
(4th percentile). Body mass index was not consid-
ered in the inclusion criteria for either group.
Study Protocol and Data Collection
Plantar pressure data have been shown to be
sensitive to the data-collection protocol.
50
Using a
pressure platform to collect data can be challenging,
particularly with children who often have trouble
staying still. We collected data as follows: the child
stood on the pressure platform and simulated gait
by walking in place to accommodate the feet to the
platform at the normal angle. After 15 sec, the child
was told to stop moving and to stand still in a
natural manner, with the entire foot on the mat and
the feet in the normal angle of gait, looking straight
ahead with the arms close to the body. The plantar
foot pressure measurements for both feet during a
30-sec period were taken simultaneously and
recorded by an independent observer. If the child
moved, the data were discarded, and the trial was
repeated until data were obtained with the child
remaining still. Aside from these cases, no ‘‘practice
trials’’ were conducted.
Gastrocnemius soleus equinus was assessed with
the knee extended and flexed. The amount of ankle
dorsiflexion was determined by using a goniometer
to measure the angle between the plantar aspect of
the heel (medially or laterally) and the tibia. Care
was taken to maintain the subtalar joint in a neutral
position and to measure ankle dorsiflexion and not
midfoot dorsiflexion (rocker bottom) or midfoot
equinus (pseudoequinus).
46
The Silfverskio
¨ld test
was performed to differentiate gastrocnemius equi-
nus from other types of equinus.
46, 51
The normal
amount of ankle dorsiflexion is approximately 108
with the knee extended and 208with the knee
flexed.
46, 52, 53
Gastrocnemius equinus is the inabil-
ity of the ankle to dorsiflex normally with the knee
extended but the ability of the ankle to dorsiflex
more than 108with the knee flexed. Gastrocnemius
soleus equinus is the inability of the ankle to
dorsiflex beyond a neutral position with the knee
extended (it remains ,08) or with the knee flexed (it
remains ,08).
54, 55
Ankle joint dorsiflexion range of motion was
performed by the same clinician with broad
experience in foot and ankle physical examinations.
The study by Evans and Scutter
56
assessed the
intrarater and interrater reliability of sagittal ankle
range of motion in children. The results show that
measures of ankle dorsiflexion in children are
Journal of the American Podiatric Medical Association Vol 101 No 1 January/February 2011 19
highly variable among examiners and, in general,
that gastrocnemius range of motion is more reliable
than is soleal range of motion. The most reliable
clinical examination of the pediatric ankle sagittal
plane range of motion has been found with knee
extension, an accepted proxy for gastrocnemius
length. Examination of ankle range of motion with
knee flexion (soleus length) has been demonstrated
to be highly unreliable.
Plantar pressures were measured by an indepen-
dent observer using a digital portable force plate
(EPS-Platform; Loran Engineering, Castel Maggiore,
Bologna, Italy). The platform dimensions were 70 3
50 cm, the thickness was 5 mm, the weight was 7 kg,
and the number of resistive sensors was 2,304.
Measurements were accurate to the nearest 0.001
kPa. The equipment met the CE Declaration of
Conformity and was calibrated a few days before
the study began. Vertical force was recorded at a
frequency of 60 Hz. The platform was linked via an
interface unit to a personal computer containing the
data-collection software program Foot Checker,
version 4.0 for Windows (Loran Engineering). The
software produced pressure maps with pressure
measured in kilopascals for each incident of data
collection.
The following static measurements were obtained
for all children in both groups: peak pressure (kPa)
under each foot, percentage of body weight sup-
ported by each limb, and plantar surface area (cm
2
)
of each foot in contact with the pedobarograph.
Statistical Analysis
The Kolmogorov-Smirnov test was used to test the
normality of the data. The results of these tests
indicated that the data were normally distributed
and that parametric statistical tests were most
appropriate. Independent Student ttests were
performed to determine whether there were statis-
tically significant differences in height, weight, and
age between the two groups. Paired Student ttests
were performed to determine differences between
the symptomatic and asymptomatic feet in the
Sever’s disease group and between the right and
left feet in the control group. Independent Student t
tests were performed to determine differences
between the symptomatic and asymptomatic feet
in the Sever’s disease group and the corresponding
feet in the control group. The association between
gastrocnemius soleus equinus and Sever’s disease
was measured by using the Pearson product
moment correlation with v
2
analysis. In all of the
analyses, P,.05 (with a 95% confidence interval)
was considered statistically significant. Data analy-
sis was conducted with SPSS software, version 14.0
(SPSS Science, Chicago, Illinois).
Results
No statistically significant differences were found
between the two groups for participant height (P,
.138), weight (P,.106), or age (P,.924), but one
was found for body mass index (P,.021). The
results for the variables measured are shown in
Table 2. In the Sever’s disease group, the sympto-
matic feet had significantly higher peak pressure
values than the asymptomatic feet (P,.001) and
supported a significantly higher percentage of body
weight (P,.001). The surface area of the foot in
contact with the pedobarograph can affect the peak
pressure measured, but no significant differences in
surface contact area were found between the
symptomatic and asymptomatic feet in the Sever’s
disease group (P..05). In the control group, no
significant differences were found between the left
and right feet in peak pressure, percentage of body
weight supported, or plantar surface area in contact
with the pedobarograph (P..05).
In the comparison between the two groups, a
statistically significant difference was found in peak
pressure between the symptomatic feet in the
Sever’s disease group and the corresponding feet
in the control group (P,.001). No difference was
found between the asymptomatic feet of the Sever’s
disease group and the corresponding feet in the
control group (P..05). A significantly higher
percentage of body weight was supported by the
Table 1. Characteristics of Children in the Sever’s Disease and Control Groups
Characteristic Sever’s Disease Group (n =22) Control Group (n =24)
Age, mean 6SD (range), y 10.45 60.80 (9–12) 10.50 60.78 (9–12)
Height, mean 6SD, cm 144.0 64.11 147.19 62.26
Weight, mean 6SD, kg 34.78 64.87 37.04 65.31
Body mass index, mean 6SD
a
16.70 61.44 17.12 61.86
a
Calculated as the weight in kilograms divided by the square of the height in meters.
20 January/February 2011 Vol 101 No 1 Journal of the American Podiatric Medical Association
symptomatic feet in the Sever’s disease group than
by the corresponding feet in the control group (P,
.001). A significantly lower percentage of body
weight was supported by the asymptomatic feet in
the Sever’s disease group than by the corresponding
feet in the control group (P,.001). No significant
difference was found in the plantar surface area of
the foot in contact with the pedobarograph between
the symptomatic feet in the Sever’s disease group
and the corresponding feet in the control group (P
..05), or between the asymptomatic feet in the
Sever’s disease group and the corresponding feet in
the control group (P..05).
A statistically significant difference was found
between the two groups in the prevalence of
gastrocnemius equinus, with all 22 children in the
Sever’s disease group having bilateral gastrocnemi-
us equinus and 21 of 24 children in the control group
having no equinus (P,.001).
Discussion
The main findings of this study were the statistically
significant differences in static peak pressure and
percentage of body weight supported between the
symptomatic and asymptomatic feet in the Sever’s
disease group. Using the asymptomatic feet as
controls eliminated many potential confounding
variables such as differences in age, weight, and
physical activity. Our results indicate that in a child
with Sever’s disease, the symptomatic foot supports
a greater percentage of body weight than the
asymptomatic foot, leading to higher pressure at
the heel of the symptomatic foot. The absence of
pain in the asymptomatic heel may be due to the
smaller load that it supports. The greater load
supported by the symptomatic heel could translate
into greater injury to the growth cartilage of the
heel. However, the asymptomatic feet in the Sever’s
disease group supported a lower percentage of body
weight than the corresponding feet in the control
group. These results indicate that Sever’s disease is
associated with abnormal distribution of body
weight between the two limbs. The control group
demonstrated a more balanced distribution of body
weight, with each foot supporting about half the
load. This may avoid overloading one heel, decreas-
ing the risk of heel inflammation associated with
Sever’s disease.
Overload in tissues may be associated with an
inability to adequately attenuate forces during gait.
Lower loading rates are widely regarded as less
damaging than higher rates. Jahss et al
57
postulated
that if force or repetition of force is not attenuated
to below a critical level, tissue destruction can
result, with healing responses leading to further
structural change and alteration of tissue mechan-
ics. This can increase forces on the heel during gait,
Table 2. Peak Pressure, Percentage of Body Weight Supported by Each Foot, and Plantar Surface Contact Area in the
Symptomatic and Asymptomatic Feet in the Sever’s Disease Group and the Corresponding Feet in the Control Group
Variable N Mean 6SD Minimum Maximum 95% CI PValue
PP (kPa)
Sever’s symptomatic foot 22 57.41 64.45 52.30 62.40 22.93 to 29.78
Control corresponding foot 24 31.05 66.73 19.40 43.60 22.98 to 29.73 ,.001
a
Sever’s asymptomatic foot 22 35.00 612.45 15.30 52.30 –2.27 to 9.30 ,.001
a
Control corresponding foot 24 31.48 66.28 22.40 43.60 –2.50 to 9.53 .227
b
PBW (%)
Sever’s symptomatic foot 22 62.24 69.22 46.50 79.40 7.90 to 17.90
Control corresponding foot 24 49.33 67.58 38.20 66.10 7.85 to 17.96 ,.001
a
Sever’s asymptomatic foot 22 37.75 69.22 20.60 53.50 –17.90 to 7.90 ,.001
a
Control corresponding foot 24 50.66 67.58 33.90 61.80 –17.96 to 7.85 ,.001
b
PS (cm
2
)
Sever’s symptomatic foot 22 24.68 66.25 18.00 49.00 –1.41 to 4.61
Control corresponding foot 24 23.08 63.64 15.00 30.00 –1.50 to 4.70 .291
a
Sever’s asymptomatic foot 22 24.36 66.14 10.00 35.00 –2.66 to 3.80 .829
a
Control corresponding foot 24 23.79 64.69 17.00 39.00 –2.71 to 3.85 .723
b
Abbreviations: CI, confidence interval; PP, peak pressure; PBW, percentage of body weight supported; PS, plantar surface area in
contact with the pedobarograph.
a
Versus Sever’s symptomatic foot.
b
Versus Sever’s asymptomatic foot.
Journal of the American Podiatric Medical Association Vol 101 No 1 January/February 2011 21
leading to repetitive microtrauma to the subcalca-
neal tissues.
58
Tax,
59
McCrea,
37
and Alexander
60
suggested that Sever’s disease is probably caused by
isolated or repeated trauma, and Madden and
Mellion,
7
Peck,
4
and Topham and White
61
noted
that anecdotal evidence supports major or minor
trauma as a probable etiology. This supports the
pathophysiological concept most often presented in
the literature of Sever’s disease as an overuse
syndrome caused by repetitive microtrauma from
increased traction on the apophysis.
8, 62-64
In a
review by Scharfbillig et al,
45
recommended treat-
ments for Sever’s disease included rest or cessation
of sports, as well as padding, which helps reduce
pressures in the heel. The authors stated that little
information had been reported on how these
treatment regimens work; further research is
needed to determine how the plantar pressures
could be relieved or affected by different forms of
treatment.
Although many authors have attempted to specify
the necessary degrees of ankle dorsiflexion, norma-
tive values have been limited.
53, 54
Biomechanically,
the maximum amount of dorsiflexion in the stance
phase of normal gait occurs just before heel lift with
the knee extended.
53
The minimum amount of ankle
range of motion necessary for normal gait is 108of
dorsiflexion and 208of plantarflexion.
53-55
The most
widely accepted values in the literature for static
measurements, and for the purpose of this study,
state that the minimum amount of dorsiflexion
necessary at the ankle for normal gait is 108of
motion.
46, 62-67
Equinus imparts a major deforming force to the
foot and is a causative factor in many foot and ankle
pathologic entities, including plantar fasciitis, pes
planus, hallux abducto valgus, Achilles tendinosis,
Charcot’s midfoot collapse, and diabetic ulcera-
tions.
55
DiGiovanni et al
54
found either gastrocne-
mius or gastrocnemius soleus equinus in patients
with a symptomatic foot and ankle. In asymptom-
atic patients, gastrocnemius and gastrocnemius
soleus equinus are not uncommon (33% and 17%,
respectively).
68
In this study, we found a 100% incidence of
bilateral gastrocnemius equinus in the Sever’s
disease group, which probably accounts for the
mechanical overload in the symptomatic heel.
Szames et al
19
evaluated 79 cases of calcaneal
apophysitis in 53 patients. They found that 82.3% of
the cases had ankle equinus due to muscular
retraction, but they did not distinguish between
gastrocnemius and soleus contracture in the equi-
nus conditions, unlike in our study. Gastrocnemius
equinus may be a predisposing factor, and increased
plantar foot pressures at the heel seem to be
associated with unilateral Sever’s disease, but
further research is needed to identify other factors
involved. A recent review of Sever’s disease by
Scharfbillig
45
found that no studies have compared
whether symptomatic patients are tighter in the
triceps surae than their asymptomatic counterparts.
However, one limitation of this study is that the
results do not allow determination of whether high
plantar pressures are a predisposing factor or a
result of Sever’s disease. Further research studies
are needed to monitor plantar foot pressures, before
or during heel pain and after heel pain has ceased,
before making a recommendation about the initia-
tion of preventive or therapeutic action. All 22
children diagnosed with Sever’s disease had symp-
toms in the left heel, and 20 of these children had
right-limb dominance, using the right foot to kick
the ball while playing soccer. Thus, it seems that the
increased amount of time during which the left foot
supports the body in ‘‘right-footed’’ athletes leads to
overload of the left heel. It is important to
investigate the relationship between limb domi-
nance and development of the disorder in a specific
foot, as other authors have done for other patho-
logic entities,
69-71
to confirm or refute this hypoth-
esis. An important limitation of this study is that
only static plantar pressures were measured. This
initial study focused on static pressures because the
children with Sever’s disease had pain during
standing.
Conclusions
Children with unilateral Sever’s disease demon-
strate higher static plantar pressures at the affected
foot than the unaffected foot and the corresponding
foot in healthy children. Thus, high plantar foot
pressures are associated with the Sever’s disease
symptoms that characterize this condition. Gastroc-
nemius equinus may be a predisposing factor for the
increased plantar pressures at the heel found in
patients with Sever’s disease and could serve as a
screening tool to indicate the need for pressure
measurements. Further research is needed to
identify other factors involved in the disease, as
well as to better understand the factors that
contribute to abnormal distribution of body weight
in the lower limbs.
Financial Disclosure: None reported.
Conflict of Interest: None reported.
22 January/February 2011 Vol 101 No 1 Journal of the American Podiatric Medical Association
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