All authors have completed the Unified Competing Interest form at
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.
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 flip-flop to report improvement. The secondary outcomes in the main reflected the primary outcomes, and there were no differences between contoured sandal and shoe insert.
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
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 [
Commonly recommended non-surgical treatments include ice, oral medication, stretching, orthoses, physical therapy, night splints, extracorporeal shock wave therapy and steroid injections [
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 [
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.
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 full-length foot orthoses) over 12 weeks in patients with heel pain. Participants were followed at 4, 8 and 12 weeks (as per
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 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 (
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 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) [
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 [
We also measured foot posture at baseline and 12 weeks. There is some conjecture as to the relationship between posture and plantar heel pain [
A research assistant who was blinded to group allocation collected data at baseline, 4, 8 and 12 weeks.
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 (
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).
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 follow-up if they did not provide GROC scores. Patients who discontinued treatment had the 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
(@ n(%), # mean (SD), * median (IQR), ^ 11 point comfort rating scale where 0 was most comfortable and 10 most uncomfortable)
Contoured sandal | Flat flip-flop | Shoe insert | |
---|---|---|---|
N(%) | 49 (33%) | 50 (33%) | 51 (34%) |
Numbers at site: | |||
Queensland (%/site) | 40 (34%) | 37 (32%) | 39 (34%) |
Victoria (%/site) | 9 (27%) | 13 (38%) | 12 (35%) |
Female@ | 32 (65%) | 38 (76%) | 32 (63%) |
Age (years)# | 52 (11) | 50 (12) | 50 (13) |
Duration weeks* | 24 (12, 56) | 22 (10, 40) | 24 (12, 52) |
Average Pain in past week* | 4 (2, 5) | 4 (2, 6) | 4 (3, 5) |
Worst Pain in past week* | 7 (5, 8) | 7 (4, 8) | 7 (4, 8) |
Other lower limb pain@ | 15 (31%) | 7 (14%) | 15 (29%) |
Foot Posture Index# | 3·9 (2·85) | 2·88 (2·85) | 2·72 (2·33) |
Comfort of device#,^ | 2·3 (1·9) | 2·3 (2·3) | 2·1 (1·8) |
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 (
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%;
(* p < 0·05)
Contoured sandal | Flat flip-flop | Shoe insert | |
---|---|---|---|
GROC week 4 | 11 (8, 13) | 8 (8, 10) | 10 (8, 13) |
GROC week 8 | 12 (8, 14) | 8 (8, 12) | 12 (8, 13) |
GROC week 12 | 13 (8, 14) | 9 (8, 14) | 13 (11, 14) |
At week 4 [Improved ≥ quite a bit better] | 14 (29%) | 5 (10%) | 14 (27%) |
Odds Ratio (95% CI) | Reference | 0·28 (0·09, 0·85)* | 0·95 (0·40, 2·27) |
NNT (95% CI) | Reference | -5 (-3, -34)* | -89 (-5, 6) |
At week 12 [Improved ≥ quite a bit better] | 27 (61%) | 16 (34%) | 27 (59%) |
Odds Ratio (95% CI) | Reference | 0·32 (0·14, 0·77)* | 0·89 (0·38, 2·09) |
NNT (95% CI) | Reference | -4 (-2, -15)* | -37 (-5, 6) |
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 (
The regression coefficients and the odds ratios are for flat flip-flop and shoe insert, with contoured sandal as reference. (* p < 0·05)
Contoured sandal | Flat flip-flop | Shoe insert | |
---|---|---|---|
Baseline | 60 (51, 68) | 60·5 (52, 67) | 58 (42, 67) |
Week 4 | 67 (58, 72) | 63 (55, 73) | 65 (53·5, 71·5) |
Week 8 | 64·5 (54, 73) | 65·5 (56, 73) | 64 (56, 72) |
Week 12 | 70 (62, 76) | 68 (57·5, 75·5) | 71·5 (58, 78) |
Change at week 12 from baseline | 10 (1, 18) | 6 (0, 12) | 8·5 (1, 17) |
Regression coefficients (effects) | |||
At week 4 | Reference | -3·3 (-8·33, 1·7) | -0·7 (-5·6, 4·3) |
At week 12 | Reference | -2·7 (-8·7, 3·2) | -0·2 (-6·2, 5·8) |
LEFS Change Category at week 4 | |||
≥ 9 | 19 (40) | 10 (22) | 14 (29) |
Odds Ratio (95% CI) | Reference | 0·44 (0·17, 1·09) | 0·63 (0·27, 1·47) |
LEFS Change Category at week 12 | |||
≥ 9 | 25 (57) | 16(34) | 24(52) |
Odds Ratio (95% CI) | Reference | 0·39 (0·17, 0·92)* | 0·83 (0·36, 1·91) |
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 (
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)).
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 [
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 [
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 flip-flop. 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 [
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The regression coefficients and the odds ratios are for flat flip-flop and shoe insert, with contoured sandal group as reference.
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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.