Corticosteroid injections compared to foot orthoses for plantar heel pain: protocol for the SOOTHE heel pain randomised trial.

INTRODUCTION: Corticosteroid injections and foot orthoses are common interventions for plantar heel pain. Previous clinical trials have found that the effectiveness of these interventions differs over time, with corticosteroid injections being more effective in the short-term (i.e. 0-4 weeks) and foot orthoses more effective in the longer-term (i.e. 5-12 weeks). However, some of these trials have methodological weaknesses that could have caused confounding and bias, which may have led to over- or under-estimation of the effectiveness of these interventions. As a result, there is a need to compare the effectiveness of corticosteroid injections and foot orthoses in a robust clinical trial with an appropriate follow-up time.
METHODS: This article describes the protocol for a pragmatic, parallel-group assessor-blinded randomised trial (Steroid injection versus foot orthoses (SOOTHE) heel pain trial). One hundred participants with plantar heel pain will be randomly allocated (i.e. two groups of approximately 50) to receive either an ultrasound-guided corticosteroid injection or prefabricated foot orthoses. Outcome measures will be obtained at baseline, 4, 8 and 12 weeks, with two primary endpoints at 4 and 12 weeks to reflect the hypothesised temporal effects of each intervention. The primary outcome measure will be the foot pain domain of the Foot Health Status Questionnaire. TRIAL REGISTRATION: Australian and New Zealand Clinical Trials Registry number ACTRN12615001266550.

Introduction

Plantar heel pain (PHP) is one of the most common musculoskeletal conditions affecting the lower limb. The worldwide prevalence of PHP in the population is unknown, however it appears to be most common in middle-aged and older people, and in runners. In a sample of the general adult population in Australia who reported foot pain, 21% reported pain in the heel [1]. An investigation of an older sample in the United States found a PHP prevalence of 6.9% [2], and in the United Kingdom, PHP accounts for approximately 7.5% of all musculoskeletal foot and ankle general practice consultations [3]. In a North American study that collected injury data on runners who presented to a sports medicine clinic over a 2-year period, the incidence of PHP was 7.9% and it was the third most common running-related injury reported [4]. PHP causes significant mobility limitation [5], [6], and individuals with PHP exhibit poorer health-related quality of life [6].

Corticosteroid injections and foot orthoses are common interventions used to treat PHP [7]. Clinical guidelines published by the American Physical Therapy Association [8] recommend foot orthoses as an initial treatment option, while the American College of Foot and Ankle Surgeons [9] recommend both corticosteroid injections and foot orthoses as initial treatment options. Previous research indicates that corticosteroid injections are more effective at reducing pain than placebo injections in the short-term (i.e. 4–6 weeks), but the effect is unclear in the longer-term (i.e. 8–12 weeks) [7]. In contrast, trials comparing foot orthoses to sham foot orthoses have reported inconsistent effects in the short-term (i.e. 3–4 weeks) [10], [11], but they have found foot orthoses are effective in the longer-term (i.e. at 12 weeks) [12], [13]. Based on this research, corticosteroid injections may be more effective in the short-term, while foot orthoses may be more effective in the longer-term. At this stage, corticosteroid injections and foot orthoses have not been directly evaluated in robust randomised trials, and consequently, nor has the temporal difference between the two interventions.

Two randomised trials have compared the effectiveness of corticosteroid injections and foot orthoses, however the findings were inconsistent [14], [15]. The trials had methodological shortcomings including high participant attrition [14], use of non-standardised outcome measures, and one trial had a relatively short follow-up period (i.e. 4 weeks) [15]. As a result, there is uncertainty regarding which intervention is more appropriate for health practitioners to recommend to individuals with PHP, or whether one should be recommended for short-term benefit, while the other recommended for longer-term benefit. Given corticosteroid injections and foot orthoses are both common interventions, it is important that health practitioners have robust evidence from which they can make decisions regarding treatment for PHP. Therefore, a high-quality randomised trial is needed to clarify inconsistencies in past research, and provide findings that can be readily adopted by health practitioners.

The primary aim of this study is to compare the effectiveness of corticosteroid injections to foot orthoses for PHP. Specifically, we seek to determine whether corticosteroid injections are more effective at reducing pain in the short-term (i.e. 0–4 weeks) and foot orthoses are more effective at reducing pain in the longer-term (i.e. 5–12 weeks). Our secondary aims are to investigate differences in ‘first-step’ pain, function, health-related quality of life, and fear-avoidance beliefs over time.

Methods

This trial has been registered on the Australian and New Zealand Clinical Trial Registry (ACTRN12615001266550). All publications related to this trial will be reported in accordance with the CONSORT Guidelines for reporting randomised trials [16].

Design

This study will be a pragmatic, parallel-group assessor-blinded randomised trial. Due to the nature of the interventions, therapists and participants will not be blinded, however the assessor measuring outcomes will be blind to group allocation (i.e. there will be assessor blinding). Fig. 1 displays the flow of participants through the trial. Participants will be allocated to one of two groups:

Fig. 1

Study flow diagram.

Group 1 – corticosteroid injection: participants will receive a single ultrasound-guided corticosteroid injection into the affected heel(s) of 1 mL of betamethasone (Celestone®, Merck Sharp and Dohme, Macquarie Park, Australia) mixed with 1 mL of bupivacaine (Marcaine®, AstraZeneca, North Ryde, Australia), a long-acting local anaesthetic.

Group 2 – foot orthoses: participants will receive a pair of Formthotics™ (Footscience International, Christchurch, New Zealand) prefabricated foot orthoses.

Both groups will also be provided a stretching program, written and verbal advice regarding PHP and wearing suitable footwear. Accordingly, the only difference between the two groups is that Group 1 will receive a corticosteroid injection and Group 2 will receive foot orthoses.

Initial appointment

Prior to the initial appointment, potential participants will be screened via telephone to ensure they satisfy inclusion criteria (as outlined in Section 2.5) that can be provided verbally. At the initial appointment, potential participants will be further screened to ensure they satisfy all remaining inclusion criteria requiring assessment (as outlined in Section 2.5). All participants will be provided with a participant information statement and will give informed consent prior to being included into the trial. Following this, participant characteristics such as sex, height, weight, duration of symptoms, foot posture (measured using the Foot Posture Index – 6), medications and major medical conditions will be recorded. Ultrasonography will be performed to assess plantar fascia thickness and the presence of hypoechogenicity. To measure plantar fascia thickness, two measurements will be recorded. A longitudinal scan will measure (i) the maximum thickness in the proximal third of the plantar fascia, and (ii) the thickness of the plantar fascia as it crosses the anterior aspect of the inferior calcaneal border. The measurements will be performed with a variable frequency (5–10 MHz) linear array transducer (Acuson Aspen; Siemens Medical Solutions, PA, USA). Measuring plantar fascia thickness as it crosses the anterior aspect of the inferior calcaneal border has been used previously [17], [18] and has good intra-rater reliability (intra-class correlation coefficient = 0.86 [95% CI, 0.77–0.92]) [19]. There is no accepted method of assessing hypoechogenicity, however previous studies have assessed hypoechogenicity as being either present or absent, which has been reported to have moderate intra-rater reliability (Cohen's Kappa ranging between 0.59 and 0.69) [19]. For bilateral cases, the most painful foot will be evaluated to satisfy the assumption of independent data [20]; this method has been used in previous heel pain research [21]. All remaining patient-reported outcome measures will be obtained at this appointment.

Intervention appointment

Following randomisation, participants will attend their second appointment where they will receive their allocated intervention. Participants randomised to the corticosteroid injection group will be referred to a radiologist at a medical imaging centre, who will perform a single ultrasound-guided corticosteroid injection into the affected heel. Participants randomised to the foot orthosis group will be referred to a podiatrist at the La Trobe University Health Sciences Clinic to have the orthoses fitted.

Randomisation, allocation concealment and blinding

Following the initial appointment for eligibility screening and inclusion into the trial, participants will be randomised to one of two groups. Randomisation and allocation to groups will be conducted using an interactive voice response telephone service provided by the National Health and Medical Research Council (NHMRC) Clinical Trials Centre at the University of Sydney, New South Wales, Australia. Adaptive stratification (i.e. minimisation) will be used to minimise baseline imbalance in the groups (factors to be included are sex, BMI and duration of symptoms), and permuted block randomisation with uneven random block sizes will be undertaken. Participants will be advised of their allocation by a secondary investigator who will not be involved with any other part of the trial. Following allocation, participants will contact one of two therapists (a radiologist for the corticosteroid injection or a podiatrist for the foot orthoses), who will arrange an appointment for the participant to receive the allocated intervention.

Given the nature of the interventions, it is not possible to blind the therapists and participants. However, the therapists will have no knowledge of, or involvement with, any other part of the trial. All outcome assessments will be conducted by the primary investigator (GAW) who will be blind to group allocation. Prior to each outcome assessment, and to minimise the chance of the outcome assessor becoming unblinded, participants will be advised not to discuss their allocated intervention during the follow-up appointments.

Interventions

Ultrasound-guided corticosteroid injection

Participants randomised to Group 1 will receive a single ultrasound-guided corticosteroid injection from a qualified radiologist (AE). The injection technique will be based on the method used by Yucel et al. [15]. Participants will be placed in a prone position with their feet hanging from the end of the examination table. Following this, an ultrasound probe will be positioned to scan the fascia longitudinally and then a 25-gauge needle will be inserted through the medial heel approximately 1 cm above the weightbearing line of the skin (Fig. 2). A solution of 1 mL of a combination of betamethasone acetate and betamethasone sodium phosphate (Celestone® Chondrose) mixed with 1 mL of bupivacaine (Marcaine® 0.5%) will be injected. Infiltration will be directed to the region surrounding the area of maximum plantar fascia thickening (i.e. there will be no infiltration into the plantar fascia itself) and aseptic technique will be maintained throughout the procedure. Prior to leaving the radiological clinic, participants will be advised to avoid running and high impact activities for two weeks. Participants with bilateral PHP will have both feet treated, and will receive the second injection the following day to ensure that there are no significant adverse events associated with the initial injection.

Fig. 2

Technique for administering the ultrasound-guided corticosteroid injection.

Foot orthoses

Participants randomised to Group 2 will receive a pair (i.e. one for each foot) of Formthotics™ prefabricated foot orthoses (Fig. 3). The style of Formthotics™ provided will be full length, and manufactured from a dual-density polyethylene closed cell foam that has a firm-density bottom layer (Shore-A durometer 50), and a soft-density top layer (Shore-A durometer 25). Participants will receive the foot orthoses in accordance with the manufacturer's instructions. The foot orthoses are initially heated and then placed in the participants' footwear. Once positioned correctly, the participants will then be asked to stand on the orthoses in a ‘corrected’ position (i.e. talo-navicular congruent position) to allow the orthoses to mould to the foot. This type of foot orthosis is an arch-contouring device that has been used in previous PHP research [12], [22]. The foot orthoses will be fitted based on the participant's foot and shoe size. Any necessary adjustments to ensure correct fitting will be made during the treatment appointment.

Fig. 3

Formthotics™ dual-density prefabricated foot orthosis.

Interventions provided to both groups

Stretching program

In addition to the experimental interventions provided (corticosteroid injection to Group 1 and foot orthoses to Group 2), participants in both groups will receive plantar fascia and calf stretches, which are regarded as ‘usual care’ and a common co-intervention in PHP research [17], [23], [24], [25], [26], [27]. The stretching program will be based on the program evaluated by DiGiovanni et al. [28]. For the plantar fascia stretches, prior to standing in the morning, the participant will cross their foot over their contralateral knee, dorsiflex their toes and ankle, and then hold the stretch (Fig. 4a). The calf stretches will be performed immediately after rising in the morning, and involve placing one foot directly behind the contralateral limb while leaning into a wall (Fig. 4b and c). Both the plantar fascia and calf stretches will be performed daily for a duration of 10 s and repeated 10 times.

Fig. 4

Plantar fascia and calf stretches: (a) plantar fascia stretch; (b) calf stretch with knee extended; (c) calf stretch with knee flexed.

Plantar heel pain and footwear education

Participants in both groups will receive education on PHP and wearing appropriate footwear (e.g. appropriately fitting footwear, suitable fixation, cushioning). Education will be provided verbally, and with a handout explaining PHP (Appendix A.1).

Outcome measures

Outcome measures will be obtained at baseline, 4, 8 and 12 weeks. The trial will have two primary endpoints at 4 and 12 weeks. Two primary endpoints (4 and 12 weeks) have been selected to ascertain if either of the interventions is more effective in the short-term or longer-term. To reduce the burden on participants in the trial, outcome measures will be either posted or emailed for the 8-week follow-up, and therefore, there will be no requirement for participants to attend in person. As a result, no ultrasound outcome measures will be reported at 8 weeks. Participants with bilateral PHP will be instructed to complete patient-reported outcome measures with respect to the most painful foot.

Primary outcome measure

The primary outcome measure will be the foot pain domain of the Foot Health Status Questionnaire (FHSQ) [29]. The FHSQ is a 13-item questionnaire used to evaluate foot-specific health-related quality of life. It has four domains or sub-scales (foot pain, foot function, footwear, and general foot health). The questionnaire uses a Likert scale format for participants to indicate their foot health from one (e.g. ‘none’) to five (e.g. ‘severe’). The foot pain domain contains four questions that measure the type, frequency and intensity of pain over the previous week. The FHSQ has been shown to be valid (content, criterion and construct), have high test-retest reliability (intra-class correlation coefficients ranging from 0.74 to 0.92), and a high degree of internal consistency (Cronbach's α ranging from 0.85 to 0.88) [29]. In addition, the minimal important difference has been calculated for the foot pain domain in participants with PHP [30]. The FHSQ has been used in previous trials investigating interventions for PHP [12], [17], [21], and a recent review recommended its use in PHP research [8].

Secondary outcome measures

Secondary outcome measures will be used to assess other issues related to pain, function (i.e. foot-related disability), and understand factors that may predict clinical outcome. These include:

Severity of ‘first step’ pain and average pain over the last seven days, measured on a 100 mm visual analogue scale (VAS) at baseline, 4, 8 and 12 weeks;

Foot function measured on the foot function domain of the FHSQ [29] at baseline, 4, 8 and 12 weeks;

Plantar fascia thickness measured sonographically [17], [18] at baseline, 4 and 12 weeks;

Plantar fascia hypoechogenicity measured sonographically [19] at baseline, 4 and 12 weeks;

Generic health-related quality of life will be measured with the EQ-5D questionnaire [31] at baseline, 4, 8 and 12 weeks;

Generic health-related quality of life will also be measured with the Short Form 36® version 2 (SF-36) [32] at baseline, 4, 8 and 12 weeks;

Self-reported physical activity measured using the 7-day Physical Activity Recall Questionnaire [33] at baseline, 4, 8 and 12 weeks;

Fear-avoidance beliefs measured using the Fear-avoidance Components Scale (FACS) [34] measured at baseline, 4, 8 and 12 weeks;

Global perceived rating of change measured with a 15-point Likert scale at 4, 8 and 12 weeks;

Days of work lost over the previous week due to PHP measured at baseline, 4, 8 and 12 weeks;

Sessions of sports or exercise lost over the previous week measured at baseline, 4, 8 and 12 weeks;

Use of co-interventions for foot pain measured at 4, 8 and 12 weeks;

The participant's preference for treatment (i.e. corticosteroid injection, foot orthoses or no preference), which will be asked at baseline [35].

Participants

Participants will be adults aged 18 years or older, who are living independently in the community. Table 1 outlines the inclusion and exclusion criteria for the study. Participants will be recruited through advertisements in local newspapers and magazines, posters placed at universities, health clubs and senior citizen centres, web-based advertising on health noticeboards and forums, and social media (e.g. Facebook, Twitter).

Table 1

Inclusion and exclusion criteria.

Inclusion criteria

(i) Aged 18 years or older;

(ii) Have a clinical diagnosis of PHP in accordance with the clinical practice guidelines linked to the International Classification of Function, Disability and Health from the Orthopaedic Section of the American Physical Therapy Association [8], which includes:a. Pain in the plantar medial heel region that is aggravated by weightbearing activities or worse in the morning and/or after a period of rest; b. Pain upon palpation of the medial calcaneal tubercle;

(iii) A duration of PHP of at least 4 weeks;

(iv) Report their average pain over the last seven days as at least 30 mm on a 100 mm VAS [36]; (v) Be willing to regularly wear foot orthoses for the duration of the trial;

(vi) Be willing and have no contraindications to receive a corticosteroid injection in the plantar heel;

(vii) Be willing to attempt to not use any other forms of treatment during the trial (with the exception of paracetamol up to 4 g/day).

Exclusion criteria

(i) Unable to understand the English language; (ii) Unable to walk household distances unaided;

(iii) Have received treatment for PHP in the last 4 weeks;

(iv) Have received a corticosteroid injection in the previous six months;

(v) Have regularly worn foot orthoses within the previous six months; (vi) Have a history of surgery to the heel;

(vii) Have a systemic medical condition such as a connective tissue disease, degenerative neurological disorder or inflammatory disorder; (viii) Currently pregnant or likely to become pregnant during the trial;

(ix) Unwilling to regularly wear footwear that can accommodate foot orthoses.

Have a clinical diagnosis of PHP in accordance with the clinical practice guidelines linked to the International Classification of Function, Disability and Health from the Orthopaedic Section of the American Physical Therapy Association [8], which includes:

Ethical approval

Ethical approval will be obtained prior to the trial commencing from the La Trobe University Human Ethics Committee. The trial will adhere to the National Health and Medical Research Council's Statement on Ethical Conduct in Human Research [37], and all participants will sign informed consent prior to inclusion in the trial.

Adverse effects

Adverse effects at the time of the corticosteroid injection will be managed and recorded in line with standard medical practice by the radiologist administering the injection. Other adverse effects, such as additional foot pain due to wearing foot orthoses or pain related to the injection, will be recorded at each time-point (i.e. 4, 8 and 12 weeks). Participants will be asked to document the type of adverse effect, and the frequency or severity of the effect. If participants experience more significant adverse effects (e.g. infection) they will be advised to contact one investigator who is not involved in recruitment, allocation or data collection (SEM or KBL). Any adverse effects will be reported in the final manuscript.

Evaluation of adherence

The evaluation of adherence will be assessed during the outcome assessments at 4, 8 and 12 weeks. Adherence to the foot orthoses will be documented, with participants being asked how many days they have worn their foot orthoses over the last week, and for how many hours each day. Both groups will also be asked to document how many days over the last week they have performed the plantar fascia and calf stretches, and whether they have changed their footwear since their last outcome assessment.

Sample size

The sample size for the trial has been determined using an a priori power analysis based on the primary outcome measure, the foot pain domain of the Foot Health Status Questionnaire (FHSQ) [29] at week 12. The minimal important difference for this measure in individuals with PHP has previously been determined as 12.5 points [30]. Using a standard deviation derived from previous PHP research of 21 [17], [38], a power level of 0.8, alpha level of 0.05, and a conservative drop-out rate of 10% (in our previous randomised trials for PHP, this has typically been <5%) [12], [17], [39], [40], a sample size of 100 participants (i.e. approximately 50 per group) will be required for adequate statistical power. We have conservatively ignored the extra precision provided by covariate analysis when estimating the sample size. This sample size will also be sufficient to: (i) explain the variance in the foot pain domain of the FHSQ at baseline, and (ii) predict improvement in the foot pain domain of the FHSQ between baseline and 12 weeks.

Data analysis

Statistical analysis will be undertaken using SPSS version 22.0 (IBM Corp, NY, USA). All analyses will follow the intention-to-treat principle [16] for all randomised participants, and missing data will be accounted for using multiple imputation, with age, BMI, baseline scores and group allocation entered as predictors [41]. For bilateral cases, the most painful foot will be evaluated to satisfy the assumption of independent data [20] – this method has been used in previous PHP research [21]. Standard tests of the distribution of continuous data will be undertaken, and transformations applied to skewed data if appropriate. If data are not normally distributed and cannot be transformed, they will be handled non-parametrically.

The differences between the two groups for primary and secondary outcome measures will be analysed at 4, 8 and 12 weeks, with 4 and 12 weeks being the primary endpoints. The primary endpoints have been chosen to allow investigation of the primary aim of the trial; that is, that there may be temporal differences in the effectiveness of the two interventions. Continuous data will be analysed using a regression approach to analysis of covariance (ANCOVA) with the baseline score for each continuous outcome measure used as a covariate [42], [43]. For example, for comparisons of pain at each of the time-points, adjustments will be made for pain at baseline. Dichotomous outcomes will be compared using risk ratios and number needed to treat where appropriate. All comparisons for outcome measures will be reported as point estimates with 95% confidence intervals and p-values.

Discussion

The primary aim of this randomised trial is to compare the effectiveness of corticosteroid injections to foot orthoses for individuals with PHP. This trial has been pragmatically designed to inform health practitioners about the effectiveness of the interventions in the short-term (i.e. 0–4 weeks) and longer-term (i.e. 5–12 weeks).

It is important to explore the effectiveness between corticosteroid injections and foot orthoses as they are both common interventions used to treat individuals with PHP, and previous trials comparing these interventions have reported inconsistent findings with respect to pain and function [14], [15]. The first trial conducted by Lynch et al. [14], was a three group trial comparing: (i) a corticosteroid injection (dexamethasone acetate) plus an oral non-steroidal anti-inflammatory drug, (ii) customised foot orthoses plus taping, and (iii) a viscoelastic heel cup. The authors completed their final follow-up at 12 weeks and concluded that customised foot orthoses were more effective than either the corticosteroid injection or the viscoelastic heel cup. However, this trial exhibited substantial participant attrition, with only 57% of participants providing outcome data at 12 weeks, and the investigators did not employ an intention-to-treat analysis. In addition, it is unclear what specific effect the corticosteroid injection had on pain reduction as the corticosteroid injection was provided in conjunction with an oral non-steroidal anti-inflammatory drug that was not provided to participants in the other groups.

The second trial by Yucel et al. [15] compared a corticosteroid injection (reported as a combined betamethasone, trade-name Kenakort-A Retard® manufactured by Bristol-Myers Squibb) to a silicone prefabricated foot orthosis. The trial found a greater reduction in VAS pain, plantar fascia thickness, and Foot and Ankle Outcome Scores (FAOS) for pain, sport and recreation, and activities of daily living in the group receiving the corticosteroid injection. However, this trial's primary endpoint was 4 weeks (i.e. short-term only).

Four additional randomised trials [17], [18], [44], [45] have evaluated corticosteroid injections against either a placebo or another type of injection. Similar to the Yucel et al. trial [15], three of these trials found a significant reduction in pain in the short-term (i.e. 4 weeks) for individuals receiving a corticosteroid injection, but this reduction was not maintained after 4 weeks [17], [44], [45]. In contrast, the fourth trial by Ball et al. [18] found a sustained effect of a corticosteroid injection (methylprednisolone acetate) compared to placebo (saline) at both 6 and 12 weeks. The inconsistencies observed in these trials may have been due to the type of corticosteroid used, with acetates (e.g. methylprednisolone acetate) tending to have a longer duration of action than phosphates (e.g. betamethasone sodium phosphate) [46].

In addition to evaluating the effectiveness of these interventions reducing pain, previous trials have also evaluated the effectiveness of foot orthoses and corticosteroid injections at improving function. Three randomised trials have found improvements in function [11], [12], [13], and the most recent systematic review concluded customised foot orthoses are more effective than sham foot orthoses at improving function up to 12 months [7]. However, there has been limited research evaluating the effectiveness of corticosteroid injections to improve function. McMillan et al. [17] included function as a secondary outcome, finding no difference between a corticosteroid injection and a placebo injection. Two previous trials that compared corticosteroid injections to foot orthoses [14], [15] included function as an outcome measure, but the findings were inconsistent between the trials. Lynch et al. [14] assessed the effect of corticosteroid injections and foot orthoses on leisure, work, and exercise, however no information was provided on how these were assessed and whether it was valid. They found no significant difference in these functional outcomes between the corticosteroid injection and foot orthosis groups at 12 weeks. In contrast, Yucel et al. [15] used the validated Foot and Ankle Outcome Score (FAOS) to assess function and health-related quality of life. After 4 weeks, FAOS activities of daily living and sport and recreation subscales improved more in the corticosteroid injection group than the foot orthosis group. Although, Yucel at al [15] used a validated outcome measure to assess function, the endpoint was 4 weeks, compared to the endpoint for Lynch et al. [14] trial being 12 weeks, which makes comparison between the two difficult. Given individuals with PHP report significant foot-related disability [5], [6], [47], it is important to better understand the influence of these interventions on function.

Regarding the experimental interventions that will be evaluated in this trial, an ultrasound-guided corticosteroid injection using betamethasone sodium phosphate combined with betamethasone acetate has been selected. There is no consensus for the most suitable corticosteroid to use for soft tissue injections, and differences in corticosteroid preference have been reported between practitioners [48]. Rheumatology guidelines published in Australia recommend two corticosteroids - betamethasone sodium phosphate combined with betamethasone acetate, or triamcinolone acetonide [49]. Betamethasone sodium phosphate combined with betamethasone acetate has been selected for use in this trial due to the combination of a long-acting acetate, which will increase potency, and a short-acting sodium phosphate which will increase solubility. This combination will balance the potency required for an anti-inflammatory action [46], against greater solubility which will decrease the likelihood of adverse effects such as plantar fascia rupture or fat pad atrophy [50]. An ultrasound-guided injection has been chosen as ultrasound-guided injections have been found to be more effective than palpation guided injections [51].

The type of foot orthoses selected for this trial are prefabricated arch-contouring devices rather than customised foot orthoses. Prefabricated foot orthoses have been demonstrated to have similar effectiveness to customised foot orthoses for PHP [52], [53]. No research has investigated what features of foot orthoses are more effective for PHP, however a few studies have investigated kinetic (i.e. plantar pressure) changes using different foot orthoses. Arch-contouring devices have been shown to reduce peak plantar pressure and maximum force at the plantar heel [22], [54], and there is some evidence to show that they reduce plantar fascia strain [55], [56]. Based on this previous research, the Formthotics™ used in this trial, which are arch contouring devices, will serve to reduce both plantar fascia strain and vertical ground reaction forces at the plantar heel. In addition, the prefabricated foot orthosis selected has been used in previous PHP research [12], [22], [54].

The additional standard care interventions (i.e. stretching program) provided to both groups have been selected to reflect clinical practice, and allow the results to be generalisable. Plantar fascia and calf stretches are commonly provided by a wide variety of health practitioners, there is no associated cost, and they have been demonstrated to be effective for PHP [28], [40], [57]. A number of randomised trials investigating PHP have provided stretches to participants in both groups [17], [23], [24], [25], [26], [27], and to reflect common clinical practice, these standard stretches will be provided to both groups in our trial.

Conclusions

This article outlines the protocol for an assessor-blinded, parallel-group randomised trial to compare the effectiveness of a single corticosteroid injection to foot orthoses for PHP. The trial has been designed to specifically investigate whether there are temporal differences between the interventions (e.g. a corticosteroid injection is more effective in the short-term and a foot orthosis is more effective in the longer-term). In addition, the trial will also assess variables that may predict clinical outcome. Finally, the pragmatic design of the trial, including a representative community-based recruitment process and commonly implemented interventions, will reflect everyday practice and ensure that the findings are generalisable.

Conflict of interest

The authors declare they have no actual or potential conflict of interest including financial, personal or other relationships that could influence or perceive to influence the conduct of this trial.

Role of the funding source

This study has been funded by a research grant from La Trobe University. In addition, Footscience International, Christchurch, New Zealand have provided the foot orthoses (Formthotics™) for free. The university and Footscience International have had no involvement in the design of the trial and will not be involved in collecting, analysing or interpreting data. Furthermore, the university and Footscience International will not be involved with writing any publication relating to this trial or decisions on where to publish.