Orthosis-Shaped Sandals Are as Efficacious as In-Shoe Orthoses and Better than Flat Sandals for Plantar Heel Pain: A Randomized Control Trial
Orthosis-Shaped Sandals Are as Efficacious as In-Shoe Orthoses and Better than Flat Sandals for Plantar Heel Pain: A Randomized Control Trial
Bill Vicenzino 0 1
Thomas G. McPoil 0 1
Aoife Stephenson 0 1
Sanjoy K. Paul 0 1
0 1 University of Queensland, School of Health and Rehabilitation Sciences , St Lucia, Brisbane, Queensland , Australia , 2 Regis University, Rueckert-Hartman College for Health Professions, Denver, Colorado, United States of America, 3 QIMR Berghofer Medical Research Institute , Brisbane, Herston, Queensland , Australia
1 Editor: Heiner Baur, Bern University of Applied Sciences , SWITZERLAND
Data Availability Statement: All relevant data are
within the paper and its Supporting Information files.
Funding: Commonwealth of Australia National
Health and Medical Research Council and Vionics
International (United States of America). The funders
had no role in study design, data collection and
analysis, decision to publish, or preparation of the
Competing Interests: All authors have completed
the Unified Competing Interest form at www.icmje.
org/coi_disclosure.pdf (available on request from the
To investigate efficacy of a contoured sandal being marketed for plantar heel pain with
comparison to a flat flip-flop and contoured in-shoe insert/orthosis.
150 volunteers aged 50 (SD: 12) years with plantar heel pain (>4 weeks) were enrolled after
responding to advertisements and eligibility determined by telephone and at first visit.
Participants were randomly allocated to receive commercially available contoured sandals (n =
49), flat flip-flops (n = 50) or over the counter, pre-fabricated full-length foot orthotics (n =
51). Primary outcomes were a 15-point Global Rating of Change scale (GROC: 1 = a very
great deal worse, 15 = a very great deal better), 13 to 15 representing an improvement and
the 20-item Lower Extremity Function Scale (LEFS) on which participants rate 20 common
weight bearing activities and activities of daily living on a 5-point scale (0 = extreme
difficulty, 4 = no difficulty). Secondary outcomes were worst level of heel pain in the preceding
week, and the foot and ankle ability measure. Outcomes were collected blind to allocation.
Analyses were done on an intention to treat basis with 12 weeks being the primary outcome time of interest.
The contoured sandal was 68% more likely to report improvement in terms of GROC compared to flat flip-flop. On the LEFS the contoured sandal was 61% more likely than flat flipflop to report improvement. The secondary outcomes in the main reflected the primary outcomes, and there were no differences between contoured sandal and shoe insert.
corresponding author). Dr. Vicenzino reports grants
from Commonwealth of Australia National Health and
Medical Research Council and from Vasyli
International for this research. Dr. Vicenzino and Dr.
McPoil are voluntary (non-compensated) members
by invitation on the Vasyli Think Tank.
Conclusions and Relevance
Physicians can have confidence in supporting a patient's decision to wear contoured sandals or in-shoe orthoses as one of the first and simple strategies to manage their heel pain.
The Australian New Zealand Clinical Trials Registry ACTRN12612000463875
Plantar heel pain that is present on first step out of bed in the morning or after a prolonged
period of sitting is emblematic of a clinical diagnosis of plantar fasciitis. It predominantly
occurs in fifth to seventh decades of life [
], and is estimated to affect 1 in 10 people over a
], cost a quarter of a billion dollars per year in the United States [
] and lead many
to consult a physician or other health care practitioner [
Commonly recommended non-surgical treatments include ice, oral medication, stretching,
orthoses, physical therapy, night splints, extracorporeal shock wave therapy and steroid
]. In-shoe orthoses, either pre-fabricated or custom made [
] are generally favoured
before the use of more invasive treatments like steroid injections [
]. However, the
effectiveness of other common treatment approaches, including sandals shaped like orthoses, is not
yet known .
Footwear companies are increasingly incorporating aspects of foot orthoses within readily
available foot wear and directly marketing to the general public without evidence of efficacy or
physician consultation. An example of this is the use of contoured slip-on sandals to manage a
myriad of lower limb ailments, including plantar heel pain [
]. Conceivably a contoured
sandal, which is quicker and easier to slip on than an orthosis in a closed in shoe, that has the
properties of in-shoe foot orthosis might confer advantages such as reducing first step pain and
would be better tolerated in hot environments where closed-in footwear with orthoses is
The objective of this study was to evaluate the efficacy of a readily available contoured
sandal in the management of plantar heel pain by comparing it to a non-contoured flat flip-flop
and a contoured shoe insert. We hypothesised that the contoured sandal would be more
efficacious than the non-contoured flat flip-flop, and similar to a contoured shoe insert.
Study design and participants
A randomized clinical trial evaluated the outcome after wearing contoured sandals compared
to wearing flat flip-flops or contoured shoe inserts (over-the-counter, pre-fabricated
fulllength foot orthoses) over 12 weeks in patients with heel pain. Participants were followed at 4,
8 and 12 weeks (as per Fig 1) by an investigator blind to allocation. The trial was conducted
across 2 Australian centres: The University of Queensland and The University of Melbourne.
The University of Queensland’s Medical Research Ethics Committee approved the trial and
all participants provided informed written consent. The Trial Registration Number is
Adults aged 18 years or older with insidious onset, non-traumatic plantar heel pain of
longer than 4 weeks duration, who responded to public advertisements between June 2012 and
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Fig 1. Flow of Participants through the study.
3 / 11
June 2013, were invited to participate. Inclusion criteria were: plantar heel pain of at least 3/10
on pain numerical rating scale (0 = no pain, 10 = worst pain imaginable) that was worse on
first steps in the morning, willingness to wear a sandal, flip-flop or contoured shoe insert for 12
weeks; own a shoe that was adequate to fit an orthosis; and an adequate competency in written
and spoken English.
Exclusion criteria were: treatment for plantar fasciitis (within past month), corticosteroid
injection during preceding 6 months; pregnancy; foot pathologies (including diabetes, gout,
amputation, nerve impingement, tumours, stress fracture, autoimmune disease, pitting
oedema, previous plantar fascia surgery); participation in more than 90 minutes per day of
athletic activity 5 or more days per week (limiting treatment of heel pain of an individual with
high levels of activity was considered inappropriate); and current use of orthosis or contoured
sandal. Eligibility was determined by telephone interview and confirmed on first visit to the
centre, after which informed consent was obtained and baseline testing performed by an
assessor blinded to allocation.
Participants were allocated a contoured sandal, flat flip flop or contoured shoe insert (Fig 2),
which were to be worn during waking hours of the 12-week study period. The contoured
sandal was a commercially available one (Vionics International, San Fransisco, USA) that has a
design that approximates that of the foot-bed of a prefabricated in-shoe foot orthosis. The
contoured shoe insert was a commercially available, over the counter, pre-fabricated full-length
foot orthotic device (Vionics International, San Fransisco, USA). The flat flip-flop was a
commercially available flat thong.
Apart from appropriate size, the key fitting guideline was that the device must be
comfortable on wearing. Upon fitting, participants were asked to rate the comfort of the device on an
11 point comfort rating scale where 0 was most comfortable and 10 most uncomfortable [
Participants were advised to contact the investigators should any discomfort occur during the
Randomization and masking
Participants were randomly allocated to an intervention (contoured sandal, flat flip-flop,
contoured shoe insert) by concealed allocation using a computer generated permuted block
schedule developed by Queensland Clinical Trials and Biostatistics Centre. A research assistant other
than the one taking outcome measures at baseline and during follow up administered this
randomized allocation and provided the participant with their allocated device.
The research assistant who performed the outcome measures was blinded to group
allocation. By the very nature of the devices, the participant and research assistant providing the
devices were not blinded.
Primary outcomes were the participants’ self-reported level of improvement on a 15-point
Global Rating of Change (GROC) scale (1 = a very great deal worse, 8 = no change, 15 = a very
great deal better) [
] and the 20-item Lower Extremity Function Scale (LEFS) [
GROC scale was dichotomised so that quite a bit better, a great deal better or a very great deal
better represented a beneficial improvement/outcome, and moderately better or less on the
scale (i.e., <13) represented no benefit. The LEFS seeks participant ratings on a 5-point scale
(0 = extreme difficulty, 4 = no difficulty) across 20 common weight bearing activities and
activities of daily living, such that a total score of 0 indicates maximum difficulty and 80 indicates
4 / 11
Fig 2. Contoured sandal, orthotic and the flat flip-flop intervention.
no difficulty with these activities [
]. The minimal detectable change and minimal clinical
important difference are both 9 points [
Secondary outcomes were the 11-point pain numerical rating scale (NRS; 0 = no pain,
10 = worst pain imaginable) of worst level of heel pain in the preceding week, and the 29-item
foot and ankle ability measure [
]. The foot and ankle ability measure is similar to the LEFS in
that it has 21-items of activities of daily living, but it also explores higher order sport activities
in a further 8-items [
]. The scores are represented as a percentage for both the activities of
daily living and sports subscales, with minimal detectable change of 5 7 and 12 3 respectively,
and minimal clinical important difference of 8 and 9 respectively [
We also measured foot posture at baseline and 12 weeks. There is some conjecture as to the
relationship between posture and plantar heel pain [
] and some evidence that foot orthoses
control the amount of foot pronation [
]. We used the Foot Posture Index as a means of
describing the foot posture in our participants with a view to evaluating if there was any
change in foot posture with wearing the devices. The Foot Posture Index is a scale consisting
of standardised ratings of visual observation of the foot [
]. The summation of the ratings is
used to score the foot as normal (0 to 5), pronated (6 to 9)/supinated (-1 to -4) or highly
pronated (10+)/supinated (-5 to -12).
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A research assistant who was blinded to group allocation collected data at baseline, 4, 8 and
The primary hypothesis was that after 12-weeks of wearing the devices, the contoured sandal
would outperform the flat flip-flops, but not the contoured shoe inserts. A total sample size of
150 participants was estimated to detect a 30% advantage on the dichotomised GROC scale for
the contoured sandal over the flat flip-flop, assuming a 25% success rate in the latter, with 90%
power, 5% type 1 error (one sided) using an online sample size calculator (http://www.stat.ubc.
ca/~rollin/stats/ssize/b2.html), and approximately a 10% drop out.
All analyses were conducted on an intention-to-treat basis. The descriptive statistics were
presented by number (%), mean (SD) or median (inter quartile range, IQR). Any missing
values at week 12 measurements were replaced by the observed measurements at week 8.
To compare the proportions for categorical data in flat flip flop and orthosis groups, with
sandal group as reference, logistic regression models were used. The odds ratios along with the
95% confidence intervals (CI) of the odds ratios were obtained, with the robust estimation of
standard errors. Analyses were adjusted for baseline measure, except for the GROC measure.
Numbers needed to treat and 95% CI were also calculated.
To compare continuous outcome variables, two approaches were used, first as continuous
variables and second as categorical variables defined by the minimal clinical important
difference at an individual participant level. The non-parametric quartile regression method was
used for the continuous data, with the baseline measure for individual outcome variables as the
adjustment factor. The regression coefficient estimates and their 95% confidence interval were
presented. The quartile regression method was used to draw inference at the median levels of
the outcome measures, due to the high skewness in the outcome variables. The categorical data
was evaluated with logistic regression models as above. Analyses were conducted using STATA
12 (Texas, USA).
A total of 150 participants with plantar heel pain were enrolled and followed up between June
1 2012 and June 28 2013, 34 participants at the research site in Melbourne and 116 at the
Queensland site. The random allocation of devices resulted in 49 participants (33%) receiving a
contoured sandal (40 participants (34%) in Queensland and 9 participants (27%) in
Melbourne), 50 (33%) receiving a flat flip-flop (37 participants (32%) in Queensland and 13
participants (38%) in Melbourne) and 51 (34%) receiving a contoured shoe insert (39 participants
(34%) in Queensland and 12 participants (35%) in Melbourne).
Fig 1 summarizes recruitment, participation, and attrition. The most common reasons for
exclusion of participants with suspected heel pain were recent other treatment for heel pain
(36%), co-morbidities (15%), incorrect pain area (13%), unable to contact or withdrew interest
(13%), and unwilling to be randomized and/or use trial devices (12%). First step pain levels too
low ( 3/10 NRS), unable to travel to the research site, heel trauma, foot and ankle surgery,
high athletic activity levels (>90min/day, 5days/week), and short pain duration (<4 weeks)
made up the remaining 11% of excluded participants. One participant in the flat flip-flop
group received a contoured sandal incorrectly. Intention to treat analysis was performed.
The trial was completed in October 2013, with 137 participants (91%) submitting primary
outcomes at 12 weeks. 13 participants (9%) were lost to follow up (unable to contact n = 10,
personal issues n = 1, increase in pain n = 2). Patients were deemed to have been lost to
followup if they did not provide GROC scores. Patients who discontinued treatment had the
6 / 11
opportunity to provide follow-up data. At 4 weeks, 143 participants (95%) completed primary
outcome measures. 7 participants (5%) were lost to follow up (unable to contact n = 5, personal
issues n = 1, increase in pain n = 1).
The characteristics of the study participants are presented in Table 1. The median duration
of plantar heel pain symptoms in the contoured sandal group, flat flip-flop and contoured shoe
insert were 24, 22 and 24 weeks respectively (Table 1). The median (IQR) of the average and
worst pain rates over the past week, determined by numerical rating scales, in the contoured
sandal group were, average: 4 (IQR 2–5) and worst: 7 (IQR 5–8); flat flip-flop group, average: 4
(IQR 2–6) and worst: 7 (IQR 4–8); contoured shoe insert group, average: 4 (IQR 3–5) and
worst: 7 (IQR 4–8).
Other lower limb pain was reported by 15 participants (31%) in the contoured sandal
group, 7 (14%) in the flat flip-flop group and 15 (29%) in the contoured shoe insert group. The
Foot Posture Index scores indicated normal foot posture (Table 1). After fitting the devices, a
mean (SD) comfort score of 2 3 (1 9) was reported for those in the contoured sandal group, 2 3
(2 3) for the flat flip-flop group and 2 1 (1 8) for the contoured shoe insert group.
As measured on both the GROC and LEFS scales at the 12-week endpoint of the study, the
contoured sandals provided greater benefit than the flat flip-flops but no difference compared to
contoured shoe inserts. The proportion of patients who reported a beneficial improvement on
GROC scores were similar between contoured sandal and contoured shoe insert groups,
however significantly higher compared to those in the flat flip flop group (61% and 59% versus
34%; Table 2). Patients in the flat flip-flop group were 68% less likely to report a beneficial
improvement compared to those in the contoured sandal group (95CI of OR: 0 14, 0 77;
p = 0 01). No significant difference was observed between the contoured shoe insert group and
the contoured sandal group (95CI of OR: 0 38, 2 09; p = 0 79).
Participants in the contoured sandal group had a clinically meaningful 10-unit increase in
LEFS score at week 12 from baseline, but neither was statistically different to the changes from
baseline observed in the flat flip-flop and contoured shoe insert groups (Table 3). However,
when participants were categorised on the basis of the minimal clinical important difference,
those in the contoured sandal group were 61% more likely to report a change in LEFS above
the minimal clinically important difference of 9 units at week 12, compared to the flat flip-flop
24 (12, 56)
4 (2, 5)
7 (5, 8)
3 9 (2 85)
2 3 (1 9)
22 (10, 40)
4 (2, 6)
7 (4, 8)
2 88 (2 85)
2 3 (2 3)
24 (12, 52)
4 (3, 5)
7 (4, 8)
2 72 (2 33)
2 1 (1 8)
quite a bit better]
quite a bit better]
group (95CI of OR: 0 17, 0 92; p = 0 01; Table 3). No significant difference was observed
between contoured sandal and contoured shoe insert group.
The improvement in worst pain over the previous week was 1 88 (/10) units better in the
contoured sandal group than the flat flip-flop group (95 CI: 0 36, 3 39, p = 0 02). No difference
was observed between contoured sandal and contoured shoe insert group (S1 Table). There
were no significant changes in the foot and ankle ability measure activities of daily living
subscale and sport subscale at week 12. Pain and foot and ankle ability measure data are presented
in S2 and S3 Tables.
The foot posture at 12 weeks as categorised by the Foot Posture Index was normal for each
of the interventions: contoured sandal (mean 3 6 (SD: 2 72)), flat flip-flop (3 02 (2 40)) and
contoured shoe insert (2 49 (2 23)).
60 (51, 68)
67 (58, 72)
64 5 (54, 73)
70 (62, 76)
10 (1, 18)
60 5 (52, 67)
63 (55, 73)
65 5 (56, 73)
68 (57 5, 75 5)
6 (0, 12)
-3 3 (-8 33, 1 7)
-2 7 (-8 7, 3 2)
0 44 (0 17, 1 09)
0 39 (0 17, 0 92)*
Adverse events in the form of increased heel pain levels were reported by participants
during the trial and occurred in both the flat flip-flop (n = 1) and contoured shoe insert (n = 1)
groups. These resulted in the participants withdrawing from the study.
Wearing contoured sandals provides a similar beneficial effect to that of a contoured shoe
insert and a superior effect to that of a flat flip-flop over a 3 month period. For every 4
patients with plantar heel pain wearing a contoured sandal, one more would be expected to be
quite a bit better, a great deal better or a very great deal better than if they wore a flat flip-flop.
The contoured shoe insert used in this study is similar to prefabricated in-shoe foot orthoses
that have been shown to be of benefit over 3 months [
]. This supports a recommendation
that the consulting physician can confidently recommend either a contoured sandal or
contoured shoe insert as one of the first strategies in managing plantar heel pain. A self-evident
advantage of a slip on contoured sandal over an orthosis in a closed shoe is that the patient
can quickly don the sandals first thing in the morning or after prolonged sitting and avoid
That the contoured sandals performed better than the flat flip-flops and similarly to
contoured shoe inserts provides further support for the use of footwear with a contoured foot
bed. Contoured footwear devices might exert their effect in a number of ways, most likely in a
similar manner as in-shoe foot orthoses. A commonly promulgated mechanism is that the
contoured device reduces rear-foot pronation [
] though the relationship between plantar
heel pain and abnormal pronation is undecided [
]. Our cohort demonstrated normal foot
posture as rated by the Foot Posture Index, both at baseline and at the end of the study,
indicating that a pronated resting foot posture is not a feature of plantar heel pain in the studied
participants and that it was not altered by wearing contoured sandals or contoured shoe
inserts. Recently we demonstrated on a radiographic and anthropometric study that the
contoured device raised the mid foot arch height more so than did a flat flip-flop and to a similar
amount as a contoured shoe insert (orthosis) [
]. Our data might reflect that there is a
temporary effect on posture by the devices but that it does not remain so after a period of
wearing. Another proposition is that in-shoe foot orthoses fill the space between the foot and
footwear and thus provide a greater degree of plantar surface contact between the shoe and
the foot. The increased contact area might distribute stress and or provide sensory input
across the plantar soft tissues including the plantar fascia and thereby help relieve pain
There are some limitations of this study that ought to be kept in mind when interpreting the
results. We did not ask if first step pain had changed, but it would be reasonable to assume that
the GROC score would be representative of any improvement or worsening of first step pain.
Compliance to device wear was not evaluated and so we were unable to ascertain if compliance
influenced the outcomes, but we did use an intention to treat analytic approach that by
definition indicates our results apply to the decision to wear the device as much as if it was worn,
how much or not at all. Another caveat on the interpretation of the results is that we were
unable to blind the patients to the device they were allocated, so a placebo mechanism might
explain the beneficial effects of the contoured sandal and contoured shoe insert over the
flipflop. However, a previous randomized placebo controlled trial reported orthoses, which were
similar to the ones used in our trial, produced beneficial effects that were superior to placebo
effects over 3 months [
]. That the contoured sandals produced similar outcomes to that of
the contoured shoe insert studied herein implies that the contoured sandals produce effects
beyond that of placebo.
9 / 11
S1 Table. Basic statistics for pain in the previous week and median difference.
S1 File. CONSORT-2010-Checklist-MS-Word.
S2 File. Protocol_OFFPHtrial.
S3 File. Ethics Approval OFFPH_20120207.
S2 Table. Basic statistics on foot ankle ability measure—activities of daily living subscale.
S3 Table. Basic statistics on foot ankle ability measure—sport subscale (FAAM-Sport,
median (IQR)), quantile regression coefficients (95% CI), categories of FAAM-Sport (n, %)
based on the minimally clinical important difference (9 points), and the odds ratios (95%
CI) for individual FAAM-Sport change categories. The regression coefficients and the odds
ratios are for flat flip-flop and shoe insert, with contoured sandal group as reference.
Kerry Mellifont and Carles Escalona contributed to study implementation and data collection.
All participants who volunteered to participate in the study. The project received funding from
the Commonwealth of Australia National Health and Medical Research Council and Vasyli
(Vionics) International. Vasyli International supplied all the footwear. The funders did not
play a role in the design or conduct of the study, nor collection, analysis or interpretation of the
data, nor preparation of the manuscript.
Conceived and designed the experiments: BV TMcP. Performed the experiments: AS BV.
Analyzed the data: SP BV. Contributed reagents/materials/analysis tools: BV TMcP. Wrote the
paper: BV TMcP AS SP.
10 / 11
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