Effects of custom insoles for symptomatic hallux valgus: protocol for a sham-controlled randomised trial

Abstract

Introduction

Hallux valgus (HV) is one of the most prevalent forefoot deformities, and its frequency increases with age, reaching nearly 23% in adulthood (females are usually more affected). Studies on customised insoles and orthoses for HV showed inconclusive results. There is no consensus in literature regarding the ideal insole or length of use for pain relief or functional improvement in individuals with HV. This study will assess the effects of a customised insole with retrocapital bar associated with an infracapital bar of the first metatarsal on pain and function of individuals with symptomatic HV.

Methods

This is the protocol for a blinded, sham-controlled randomised clinical trial. Eighty participants with symptomatic HV will be randomised into two groups (40 per group): customised insole or sham insole. Assessments will be performed at baseline (T0), six (T6) and 12 weeks (T12) of intervention. A follow-up will occur after 4 weeks of intervention (T16). The primary and secondary outcomes will be pain (Numerical Pain Scale) and function (Foot Function Index), respectively.

Statistical analysis

Analysis of variance with a mixed design or Friedman’s test will be considered according to data distribution; post-hoc analyses will be performed using Bonferroni test. Time × group interaction and within-group and between-group differences will also be assessed. The intent-to-treat analysis will be used. A significance level of 5% and 95% s will be adopted for all statistical analyses.

Ethics and dissemination

This protocol was approved by the research ethics committee of the Faculty of Health Sciences of Trairi/Federal University of Rio Grande do Norte (UFRN/FACISA; opinion number 5411306). The study results will be disseminated to participants, submitted to a peer-reviewed journal and presented in scientific meetings.

Trial registrations number

NCT05408156.

Correspondence to Marcelo Cardoso de Souza; [email protected]

Strengths and limitations of this study

• This study suggests a new approach using customised insoles that include a retrocapital bar and an infracapital bar of the first metatarsal for individuals with symptomatic hallux valgus.

• This study aims to demonstrate the long-term effects of customised insoles (longer than 12 weeks) by conducting a follow-up of 16 weeks.

• This study will fill an existing gap in orthoses prescription for hallux valgus since neither consensus nor recommendations exist on the use of customised insoles.

• Adherence to using insoles for at least 6 hours/day and filling in the diary are possible limitations that will be mitigated via telephone monitoring.

• We suggest blinding the participants and researchers involved in the assessments.

Introduction

Hallux valgus (HV) is a structural misalignment of the first metatarsophalangeal joint, resulting in lateral deviation of the hallux with medial deviation of the first metatarsal.^1–3 These deviations cause pain and limit daily activities, such as walking, going to the supermarket and working.⁴

The development of HV is linked to extrinsic (eg, narrow-fitting shoes) and intrinsic factors, such as genetic predisposition, ligament laxity and biomechanical abnormalities of distal and proximal joints.^{3 5–11} Nearly 23% of HV-related deformities occur in adulthood, being more frequent in females.^{3 5}

HV is diagnosed when the abduction angle is greater than 15° on the radiological examination.² However, this examination is often unavailable in many health centres and medical offices. Simpler and easier methods, such as the Manchester Scale, can diagnose and classify the degree of HV deformity.^12–16

According to the Manchester classification,¹⁶ the greater the deformity degree, the lower the gait speed and the greater the pain, functional limitation and muscle weakness.^{3 17 18} Therefore, interventions that minimise functional limitations and reduce pain are important for individuals with HV.^{18 19}

The conservative treatment aims to mitigate symptoms and should be the first option when HV is diagnosed.² This treatment usually includes rigid or dynamic orthoses, customised insoles, splints, shoe modification and specific foot exercises.^{2 3 11 20} In particular, insoles may help relieve pain, improve abnormal foot function and prevent other forces from acting on the metatarsophalangeal joint.^{11 21 22} Nevertheless, evidence on the effects of orthoses and insoles for individuals with HV is inconclusive.^22–26

A systematic review²⁴ concluded that dynamic and static orthoses with a toe separator effectively reduced the HV angle and pain. Also, according to Chadchavalpanichaya et al, the use of a customised silicone toe separator for 12 months promoted a moderate decrease in pain and HV angle (reduction of 3.3° measured using anteroposterior photography).²⁵ Another study showed decreased HV angle and improved pain and walking ability after using a full-contact insole with a toe separator for 3 months.²⁶

Given the lack of consensus on the ideal insole or its length of use for individuals with HV, we suggest a customised insole with retrocapital bar and an infracapital bar of the first metatarsal to increase the contact surface of the forefoot and contribute to reducing pain and pressure in the metatarsal region.^27–29 The new approach suggested in this protocol may help health professionals successfully manage individuals with symptomatic HV by applying a conservative treatment based on customised insoles. Therefore, this study aims to assess the effects of a customised insole on pain and function of individuals with symptomatic HV. We hypothesised that customised insoles would reduce pain and improve function in individuals with symptomatic HV compared with sham insoles.

Methods

Study design

This protocol for a blinded, sham-controlled randomised clinical trial was approved by the research ethics committee of UFRN/FACISA (protocol number: 5 411 306). Participants will be randomised into two groups (customised insole group (CIG) and sham insole group (SIG)) of 40 participants (figure 1). The study is reported according to the Consolidated Standards of Reporting Trials (CONSORT),³⁰ the Template for Intervention Description and Replication (TIDieR) and the Standard Protocol Items Recommendations for Interventional Trials (SPIRIT).³¹

Figure 1. Flow diagram of individuals throughout the study according to CONSORT. CONSORT, consolidated standards of reporting trials; HV, hallux valgus.

Participants

The sample size was calculated based on Costa et al,³² who conducted similar methods to detect a minimal clinically important difference of 1.5 points between groups using the Numerical Pain Scale (NPS) as primary outcome. We considered an estimated SD of 3.2, a statistical power of 80%, a 5% alpha and a 10% loss of follow-up. Therefore, 80 participants will be needed (40 in the CIG and 40 in the SIG).

Participants will be recruited via social media campaigns, using the communication channel of the Hospital Universitário Onofre Lopes (HUOL-UFRN), and the waiting list of HUOL-UFRN Rehabilitation Unit. The secretary will contact participants via telephone to schedule an initial screening, which will always be performed by a single researcher. Eligible individuals will be informed about the study objectives and procedures and will sign the informed consent form.

Data collection will include personal information (name, address and telephone number), anthropometric data (age, height and body mass index), sociodemographic data (profession, ethnicity, income and education), clinical history of the disease, foot function (Foot Function Index (FFI)), HV deformity degree, pain intensity and plantigraphy. Data will be numerically encoded and stored in a database to maintain the study blind.

Inclusion criteria

• Male and female participants aged 18 or more.^33–35

• Mild to moderate HV according to the Manchester Scale.^{19 22 35}

• Pain in the hallux or the metatarsophalangeal joint or both between 3 and 8 points, according to the NPS.¹⁹

• Available to actively use the customised insole for at least 6 hours/day inside the preferred closed footwear.

Exclusion criteria

• Undergoing physical therapy treatment for HV concomitantly with the study.¹⁹

• Previous HV surgery.^34–36

• Wound and foot injuries, dislocations or metatarsophalangeal fractures in the same foot of the HV in the last 5 years.³³

• Rheumatoid arthritis, decompensated diabetes, gout or neurodegenerative diseases and other sensory and motor disorders.^{9 33}

• Cognitive and mental disorders affecting the ability to read, understand and answer the questionnaires and terms related to the study.³⁷

Discontinuity criteria

• Individuals not showing up to remove the insole after the first assessment (T0).

• Individuals reporting the use of the insole for less than 6 hours/day.

• Individuals refusing to wear the insole after being included in the study.

Research team

This study will involve five researchers with different responsibilities: (A) screening of participants and blinded assessments; (B) randomisation; (C) customisation of insoles and delivery to participants; (D) data tabulation and (E) statistical analysis.

Randomisation and blinding allocation

Researcher A will screen participants. Eligible individuals formally agreeing to participate in the study will be assessed and randomly allocated into one of two groups (CIG or SIG) by researcher B. We will use opaque, sealed and sequentially numbered envelopes to blind the allocation procedure. The randomisation sequence will be conducted using the website www.sealedenvelope.com. Researcher B will not be involved in any other phase of the study.

Blinding

Initial assessments will be performed by researcher A, who will not be involved with interventions and remain blind to group allocation. A plantigraphy containing all anatomical points will be performed to allow insole manufacturing. Researcher C, who has 10 years of experience making insoles, will be responsible for customising the insoles. Participants allocated to CIG will receive their insoles 5 days after the initial assessment.

Participants will be identified only by numbers and informed about the study objective. All participants will undergo the same assessments before manufacturing and delivering the insoles to avoid compromising the study blinding. Participants will be scheduled to receive the insoles at different times to avoid potential meetings or exchange of information.

The blinding strategy will be assessed after intervention completion (T12) by asking participants which intervention they believe they have received. The information about group allocation will only be revealed after the last follow-up (T16). Researcher D will tabulate data after the final assessment. Researcher E will be responsible for the statistical analysis and will not participate in the previous stages of the study. The flowchart of data collection and analysis is outlined in figure 2.

Figure 2. Researchers involved in each stage of the study.

Procedures and intervention

Assessments for insole prescription and customisation will be conducted at the Laboratory of Insoles and Rheumatology (LAPRE, HUOL-UFRN). Data collection will start in August 2024 and end in December 2025. Participants will undergo an initial assessment (T0) of clinical and functional characteristics related to pain in the forefoot (pain, function, classification of HV deformity degree, pain catastrophising and treatment expectation), followed by a plantigraphy. The latter will produce a printed version of plantar surfaces that will guide insole customisation. After this stage, participants will be randomised.

Participants allocated to the CIG will receive a semi-flexible non-moulded insole with 2.5 mm coverage with Shore A 28, a 5 mm retrocapital bar with Shore A 22 and a 2 mm infracapital bar of the first metatarsal with Shore A 35. All insoles will be manufactured in ethylene vinyl acetate (EVA) by researcher C. The customised insole will be used on both feet (figure 3A) to maintain the symmetry between limbs and comfort, given this is not a corrective intervention. The SIG will receive the same non-moulded insole manufactured in EVA with a semi-flexible base and 2.5 mm coverage with Shore A 28, but without bars used in the CIG (figure 3B).

Figure 3. Customised insole (A) and sham insole (B).

Customised insoles will be delivered for each participant within 5 days after the initial assessment. After collecting the insoles, participants will be instructed on how to use and conserve them. Instructions will be focused on using insoles for at least 6 hours/day in closed shoes that are not tight after insertion of the custom insole. It will also be reinforced that the participant remove the original insole from the footwear for placement in the new insole. This guidance given become a barrier to the acceptability of the intervention, as individuals have aesthetic concerns regarding their footwear. It is known that the aesthetics of footwear is a common and unavoidable problem in this type of study, as they have a unique role as both treatment and clothing.³⁸ In case of discomfort, participants will be instructed to return for adjustments. The foot elements defined for this study and adapted in the customised insole aim to reduce the overload in the metatarsal region and distribute the pressure on foot structures, minimising pain.^27–29

A second assessment (pain and function via telephone) will be performed 6 weeks after insole delivery (T6). The outcomes assessed at T0 will be reassessed in person after 12 weeks (T12). Participants will be informed about intervention completion at this stage, followed by the blinding test to verify the effectiveness of the study blinding. Finally, participants will be contacted via telephone 4 weeks after intervention completion (T16) for follow-up assessment. All assessments will be performed by the same researcher to standardise the procedures.

Before each assessment, participants will be asked about using analgesic resources (eg, analgesic or anti-inflammatory drugs, ice, heat or any other non-pharmacological initiative) to manage pain related to HV or other body parts.

Assessments

Sample characterisation will include age, education level, anthropometric data, clinical data (eg, disease history, symptom onset), pain catastrophising and HV deformity degree.

The Pain Catastrophising Scale (PCS) consisting of 13 items will be used to assess pain catastrophising.^{39 40} Participants must report the degree of catastrophic thinking or feeling related to pain using a 5-point Likert scale. The instrument has three subscales: helplessness, magnification and rumination. The final score is the sum of items and varies from 0 to 52 points; higher scores indicate greater pain catastrophising.^{39 40}

The Manchester Scale will characterise the HV deformity degree in the initial assessment (T0) by matching a set of standardised photographs of HV deformity. Deformity will be classified as none (0), mild (1), moderate (2) or severe (3) (figure 4).^{13 16 41} The Manchester Scale has a high intra-tester (ICC between 0.92 and 0.99) and inter-tester (ICC between 0.87 and 0.96) reliability⁴¹ and is associated with radiographic measurements. Therefore, this scale is recommended for clinical and research purposes.^{42 43}

Figure 4. Hallux valgus deformity characterized by Manchester Scale: none (A), mild (B), moderate (C) and severe (D). This figure was reproduced with permission by APMA and appeared in Garrow et al. 16

Primary outcome

Pain

Pain intensity will be assessed using the NPS, a numerical scale ranging from 0 (no pain) to 10 points (worst pain possible).^{19 41} This assessment will be performed at rest and after the following functional tests: going up and down stairs, walking 40 m and sitting and standing.^{19 41}

Secondary outcomes

Function

Function will be assessed using the FFI, a questionnaire developed to measure the impact of foot pathologies and symptoms (pain, disability and activity restriction) on foot function. The FFI consists of 23 items grouped into three subscales: five items related to disability, nine items related to pain and nine items related to activity limitation.³⁴ The average of all domains provides a final score ranging from 0% to 100%, which is proportional to foot functional impairment.^{44 45}

Treatment expectation

Treatment expectations will be assessed using a 5-point Likert scale. The following will be asked to participants at T0: ‘Do you think that by using customised insoles, you will: 1—get much worse, 2—get worse, 3—no changes, 4—improve or 5—greatly improve?’

Self-assessment of treatment

A 5-point Likert scale will be used to assess satisfaction with the intervention. Participants will be asked the following question: ‘How are you feeling after using the insoles?: 1—much worse, 2—worse, 3—no changes, 4—better or 5—much better’.

Blinding test

Participants will be asked in which group they believed they were allocated: CIG or SIG. This strategy has been recommended at the end of clinical trials to test whether the blinding strategy adopted was effective.⁴⁶

Hours of insole use

Participants of both groups will receive an insole control diary to register the number of hours per day spent with the insole. Participants should keep the diary for 12 weeks and return it to researchers at T12. Monitoring and motivation will be performed via telephone or WhatsApp messages to prevent participants from forgetting to use the insole.

Use of analgesic modalities

Participants will also receive an Excel sheet to track the analgesic modalities used daily to manage pain related to HV or other body parts during the study period. Table 1 presents the primary and secondary outcomes and instruments used in each study stage: T0, T6, T12, and T16.created by the authors.

Table 1

Protocol items reported according to the Standard Protocol Items Recommendations for Interventional Trials (SPIRIT)

Time point	Screening	Baseline	Study period postallocation
	− T1	T0	6 weeks T6	12 weeks T12	16 weeks T16
Enrolment
Eligibility criteria Informed consent Group allocation	X
	X
		X
Interventions
Customised insoles
Sham insoles
Assessments
Pain—NPS Foot Function—FFI Deformity degree—Manchester Scale		X	X	X	X
		X	X	X	X
		X
Plantigraphy Catastrophising pain—PCS Patient expectation		X
		X
		X
Satisfaction with the treatment Use analgesic resources				X	X
		X	X	X	X
Blinding test				X	X

Created by the authors.

FFI, Foot Function Index; NPS, Numeric Pain Scale; PCS, Pain Catastrophising Scale; SPIRIT, Standard Protocol Items Recommendations for Interventional Trials.

Involvement of participants and the public

Participants will not be involved in the study design, development of the research question or recruitment procedures. After intervention completion, the results can be shared with participants in a lecture. If one insole shows statistically significant better results than the other, the most effective intervention will be offered to the other group.

Researcher training

A series of training steps focused on the performance of assessments, manufacture of customised insoles and instructions for insole use will be conducted before the study begins. This training aims to standardise the activities conducted in the study and facilitate a consensus among the researchers involved.

Statistical analysis

Data will be analysed by a blinded statistician using commercial software. The independent variables of groups (CIG and SIG) and time (T0, T6, T12 and T16) will be considered for each dependent variable (pain and function) in all assessment times. Kolmogorov–Smirnov test will verify data distribution, and Levene test will analyse the homogeneity of variance.

If data are normally distributed, an analysis of variance with a mixed design will be conducted for the primary and secondary outcomes, considering group × time interaction as the main result. The Friedman test will be used if data are not normally distributed. Finally, the Bonferroni test will be used in post-hoc analyses to determine differences between groups at different intervention times.

Missing data will be managed by imputing data from the last assessment. An intention-to-treat analysis will ensure randomisation and uniform distribution of prognostic factors between groups. All statistical analyses will adopt a significance level of 5% and 95% CI.

Discussion

This protocol for a blinded, sham-controlled randomised trial aims to assess the effects of customised versus sham insoles for individuals with symptomatic HV. Participants will be assessed during 12 weeks of intervention, and a follow-up will be conducted after 4 weeks of intervention completion.

Our study presents a new customised insole model for individuals with symptomatic HV that includes a retrocapital bar and an infracapital bar in the first metatarsal. With these supporting structures, we hypothesise a decreased overload in the metatarsal region due to the reallocation of pressures in foot structures, contributing to pain reduction.^{29 37 47}

Despite the lack of robust and sufficient scientific evidence recommending insoles for individuals with HV, several models are presented in literature, such as semi-rigid full-contact insoles moulded with the joint in neutral position, manufactured in a ¾ polypropylene base with forefoot extension in EVA;³³ contact insole manufactured in thermoplastic elastomer in three lengths (full base, infracapital base and retrocapital base);³⁴ and full-contact insole moulded in neutral position, manufactured in plastazote poron and adapted with a silicone toe separator.²⁶

Previous studies used several treatment lengths to assess the effects of customised insoles in the targeted population, including 1 month,^{19 22} 3 months,^{25 34} 6 months²³ and 12 months.⁴⁷ We outlined a time of 3 months because studies conducted within this period demonstrated adequate methodological designs and less risk of bias than other studies.

The unrestricted use of analgesic resources to reduce pain during the study might be considered a limitation; thus, we will ask about the use of analgesic resources (pharmacological or not) before each assessment. Another possible limitation will be filling the diary with information regarding insole use (hours per day). For this, close monitoring and reinforcement will be conducted via telephone (ie, calls or WhatsApp messages).

Literature lacks information about the effectiveness of conservative treatment for HV, and the available studies demonstrate considerable methodological limitations. Therefore, this protocol adopts all necessary procedures to develop a study with high methodological quality. The procedures and outcome measures were well defined, and the study design included adequate randomisation, sample size and blinding of researchers. In addition, we will assess the self-reported use of analgesic resources during the intervention and perform an intention-to-treat analysis. We also included a 1 month follow-up to verify the short-term and mid-term effects.

Therefore, given the lack of consensus on the most effective type of insole and standardisation regarding its use, this sham-controlled randomised clinical trial protocol will serve as a basis for future studies and contribute to guiding evidence-based prescription and clinical use of customised insoles.

Ethical approval, consent to participate, and disclosure

This study was approved by the research ethics committee (opinion number: 5,411,306) of the Faculty of Health Sciences of Trairi – Federal University of Rio Grande do Norte (UFRN/FACISA). We followed the guidelines and regulatory standards for research involving human in Brazil according to Resolution 466/12 of the National Council for Ethics in Research (CONEP). The informed consent form will be explained to participants, and one copy will be given to them. The ethical principles stated in the Declaration of Helsinki will be respected in all study procedures. We will ensure respect for individuals and the maintenance of their autonomy. Participants will be informed about the study objectives, risks and benefits. Participants must sign the informed consent form before taking part in the study and will be free to withdraw from the study without obligation to provide any explanation. This study protocol is registered on ClinicalTrials.gov with the identifier NCT05408156. Results will be disseminated to peer-reviewed journals, lectures and scientific meetings.

The authors thank Probatus Academic Services for providing scientific language and

translation.

Ethics statements

Patient consent for publication

Not required.

Footnote

Contributors Study conception and design: RRC, AAMTM, GMB and MCdS. Data analysis: GMB. Drafting of manuscript: all authors. Critical revisions: all authors. Final approval of the article: all authors. Funding: MCdS. Responsible for integrity of the study ([email protected]).

Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

Competing interests None declared.

Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting or dissemination plans of this research.

Provenance and peer review Not commissioned; externally peer reviewed.

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