Effect of Customized Foot Insoles and Textured Insoles on the Balance and Postural Control in Elderly with Pes Planus: A Randomized Controlled Trial

Introduction

Falls are prominent among the external causes of unintentional injuries, while unstable balance ranks high amongst serious clinical problems faced by older adults. They can be attributed for substantial rates of mortality and morbidity among older individuals and are also considered as major contributors to immobility and premature nursing home placement.¹ Globally, approximately 28-35% of people aged 65 years and above experience falls every year, and this incidence can go as high as 32-42% in individuals over 70 years. Around 30-50% of individuals residing in long-term care facilities report experiencing falls annually, with 40% of them encountering repeated incidents.²

In India, a ‘senior citizen’ or ‘older adult’ is defined as ‘a person aged 60 years and older’. This is the fastest growing population in India, increasing from 6.7% in 1991 to 10% in 2021. In India, the occurrence of falls among adults aged 60 years and older was documented to range from 14% to 53%.³ Falls are considered as the primary cause of injury among adults over the age of 65, and each year one in three older adults report having had a fall, according to the Centers for Disease Control and Prevention.⁴ Human aging causes physiological changes such as decreased postural balance, thus increasing the risk of falls. Postural stability maintenance is strongly influenced by the tactile sensitivity in the foot.⁵ It is also dependent on a range of somatosensory inputs. The postural stability and balance are influenced by the position of center of mass of the body and its displacement within the base of support.⁶

The foot serves as the initial point of contact between the body and outside world, playing a significant role in postural stability.⁷ Its plantar mechanical receptors provide crucial spatial and temporal information regarding contact pressures and shear forces resulting from body movements. This acts as a valuable feedback mechanism for the postural control system.

Textured insoles are simple interventions that can serve as affordable adjuvant interventions for improving balance among the elderly, excluding the need of podiatric assistance. Textured insoles enhance the foot sensitivity, allowing the brain to automatically correct the position before the wobble occurs. Much of positive evidence is available in the literature on the benefits of textured insoles. Customized insole with ethylene vinyl acetate material was used for the contact surface of the feet. Additionally, the heel cup with an arch support insole improved the contact surface of the foot, enhancing the ankle, standing, and ambulation stabilities.⁸ This study aimed to assess and compare the effectiveness of flat and textured insoles among elderly people with pes planus and foot pain.

Materials and Methods

The study was approved by the Institutional Ethical Review Board (IERB), Mobility India Rehabilitation Research and Training Centre with application number MI/IERB/006/2021.

This study sought to examine the impact of flat or textured surface insoles on balance and postural support among the elderly population.

Design and Study Settings

A randomized controlled trial was conducted to assess the effect of two different insoles (customized or textured) on the balance and postural control in the elderly population in comparison with a control group without orthoses. It was conducted from April 2022 to July 2022 in Mobility India Rehabilitation Research and Training Centre, Bangalore and an old age home in Bangalore. The study trial was approved by the Rajiv Gandhi University of Health Sciences Research Committee.

Study Subjects

The participants considered for the study were adults aged ≥ 60 years with the ability to read and write in English, Kannada, Tamil, Hindi. For few subjects, the consent form was translated to their native language and the information about the study was explained either to the caretaker or the guardian.

Inclusion criteria considered were community dwellers, aged ≥ 60 years with ambulation, without any assistive devices or assistance, with previous history of falls and balance issues with regards to foot (slippage, grip, surfaces) recorded using a simple two step questionnaire, with pes planus of foot and pain in the plantar foot.

The exclusion criteria considered were as follows: individuals who were non-ambulatory, those with a history of vestibular diseases, pathologies affecting the central nervous system (such as stroke, dementia, Parkinson's disease), prior diagnosis of peripheral neuropathy, individuals who had used insoles in the past six months, those with a history of foot surgery, and lower limb amputations. Additionally, participants with lower limb ulcers, impaired tactile and thermal sensitivity, severe foot deformities, difficulties accommodating insoles within their footwear, and those unable to comply with the necessary re-evaluations or instructions of the research protocol were also excluded. Tactile sensitivity was assessed by examining subjects using a finger.

Participants were directed to indicate positively whenever they felt the touch of a finger at each of the ten specified sites on the foot (including the plantar aspects of the 1st, 3rd, and 5th digits; the plantar aspects of the 1st, 3rd, and 5th metatarsal heads; the plantar medial and lateral sides of the midfoot; the plantar area of the heel; and the dorsal aspect of the midfoot).

Sampling Technique

Sampling technique is the procedure in which the researcher adopts the selection the study sample. For the present study, probability randomization of the eligible participants was done by random number allocation, assignment was done by patient preference (partially randomized patient preference approach). Open label trial sampling technique was selected and considered appropriate.

Fabrication of Intervention

Included subjects were informed prior regarding the intervention being conducted. Before the commencement of the study, subjects were explained about the procedure and purpose of the study. Clinical assessments were conducted on subjects’ balance issues, postural sway, foot pain, pes planus, followed by Berg balance score (BBS) and time up and go (TUG) test.

Intervention

The subjects in the intervention group were provided with a customized or textured 3 mm thick insole made of ethylene-vinyl acetate (EVA) with a customized or textured surface. Small pyramidal peaks covered the entire surface of textured insole with a center-to-center distance of ~2 mm (Figure 1).

The insoles were tailored to fit the subjects' shoe size as per Orthoses and Prostheses standards, and they were placed inside their regular shoes for wearing. Materials used in the fabrication of intervention included, negative cast obtained from plaster of Paris bandage, high density ethyl vinyl acetate (flat and textured) - 3 mm, high temperature thermoplastic (polypropylene) - 3 mm and a marking pen.

Procedure of Data collection

Randomization

All eligible participants were randomly allocated to one of the intervention groups receiving insoles (Group 1/G1 with customized insoles and Group 2/G2 with textured insoles) or to the control group (CG3) without orthoses. Randomization was conducted using a sequential number random group allocation method. Randomization of the eligible participants was done by random number allocation assignment considering patient preference (partially randomized patient preference approach) with open label trial.

Partially Randomized Patient Preference Trial (RPPT)

Over the years, several approaches with different nomenclature have been proposed as alternative designs to mitigate the impact of patients’ preferences on validity. Few of those are RPPT, a comprehensive cohort trial, a patient preference trial. In general, these designs aim to treat patients considering individual treatment preferences, while only the patients without any specific preference would be randomized in the conventional manner. In the present era where patients are actively involved in the research, RPPTs becomes more relevant.

RPPTs present findings from both randomized and preference cohorts within trials where both cohorts meet the same inclusion and exclusion criteria and undergo the same treatment protocol. In trials employing a two-stage randomized design where allocation is based on patient preference, data for the randomized and preference cohorts are not separately available.⁹

Statistical Methods

Descriptive and inferential statistical analysis was carried out using Statistical software SPSS 22.0. Data on continuous measurements were presented as mean±SD (Min-Max) and data on categorical measurements were presented as number (%). Significance was assessed at 5% level of significance.

The one-way analysis of variance (ANOVA) was utilized to ascertain whether there were any statistically significant differences among the means of three or more independent (unrelated) groups.

Analysis involves calculating specific measures and examining patterns of relationships among data sets. Generally, data analysis encompasses several closely linked operations aimed at summarizing collected data and organizing it to address research questions. This section focuses on analyzing and interpreting data gathered from thirty elderly individuals, both with and without insoles. The present study aimed to assess the effectiveness of the customized insoles and textured insoles in maintenance of balance. Collected data were coded, tabulated, organized, analyzed, and interpreted using descriptive and inferential statistics.

Results

Forty-five subjects were subsequently randomized: 14 in G1 received customized insoles, 15 in G2 were provided with textured insoles, and 16 in CG did not use any insoles. In G1, four subjects were lost due to personal reasons. In G2, five subjects were unable to adapt to the intervention due to discomfort from feeling warmth in their feet while using the insoles, and three subjects reported the same issue. Six subjects in the control group could not attend the reassessment due to personal reasons. Therefore, final analysis was conducted including thirty subjects (10-G1, 10-G2, 10-CG).

No significant differences were found between the groups at baseline when the socio-demographic and clinical data, fall history, Visual Analogue scale (VAS), BBS, and TUG test were considered.

In this study, a total of 30 elderlies were enrolled. The mean age and standard deviation of the subjects in intervention group 1 was 75.5±13.51 years, intervention group 2 was 71.2±9.74 years and the control group was 64.6±3.37 years. No significant difference was found between the groups.

Gender

Frequency of gender distribution in three groups of patients studied was 21 females and 8 males.

VAS

Frequency distribution of VAS scores among the three groups of patients was as follows: Mean±SD in Group 1- 6.20±1.75, Group 2 - 4.70±0.94, Group 3 - 5.70±1.49. A VAS score of 1-3 was reported by two elderlies, a score of 4-6 was reported by nineteen elderlies, while a score of 7-10 was reported by nine elderlies.

Fall history

Frequency distribution in terms of the number of falls among the three groups of patients included a minimum of one fall history to a maximum of three falls. In this study, 17 subjects had experienced at least one fall during the last six months to one year period, 11 subjects experienced two falls, while two subjects experienced three falls in the last six months to one year.

Outcome measures pre and post-interventions are shown in Tables 1 and 2. A significant difference was observed in the TUG eight weeks post-intervention. Berg balance scale was used as the outcome measuring tool of balance in pre and post-tests. The comparison between the three groups is shown in Table 1. No significant difference was noted between the groups.

ANOVA was used for between group analysis, while Student t test (paired) was used for within group analysis

Time up and go test was used as the outcome measuring tool for speed. The comparison between the three groups before and after intervention is shown in Table 2. No significant differences were observed between the groups.

ANOVA was used for inter group analysis, while Student t test (paired) was used for intra group analysis

There was a significant difference found in the post test values of TUG. The significant difference found in the Group 2 which used textured insole could not be generalized due to the small sample size. Further research with larger sample is required to establish the effectiveness of the intervention.

In this study, a significant difference in TUG scores in Group 2 (Textured insole) were observed with the following significant values:

+ Suggestive significance (P value: 0.05<P<0.10)

* Moderately significant (P value: 0.01<P ± 0.05)

** Strongly significant (P value: P ± 0.01)

Discussion

In our study, a flat EVA material was frequently employed as the foundation for customized foot orthoses, while textured EVA was primarily utilized for insoles. Subjects underwent evaluation after eight weeks, revealing noticeable benefits. There is currently no available data on the frequency of insole usage required to achieve improvements in balance and sway. However, it was observed earlier that there was evidence of immediate improvement in postural sway following the intervention.¹⁰ Here, duration of insole wearing did not impact BBS and TUG response. The benefits were evident even with brief periods of using foot orthoses. However, the optimum insole wearing time necessary to achieve significant results is yet to be determined.

Customized foot orthoses were investigated which showed certain evidence of balance improvement following a short follow-up period (2-8 weeks).⁸ The interventions comprised personalized prescriptions, insoles featuring arch support, and a heel cup with arch support. In a previous study, we noted enhancements in balance (measured by BBS and TUG) among 89 elderly women with osteoporosis who used insoles with arch support and a metatarsal pad in a four-week randomized controlled trial.^8,11

While these orthoses are widely accessible and generally well-received, some individuals may require podiatric assistance. Surface insole modifications could represent a simpler intervention when compared to vibration therapy or custom-made insoles. Limited research on balance assessment using textured surfaces on insoles or shoes has yielded diverse outcomes. Maki et al. observed improvement in balance in both younger and older subjects on using an insole with edge elevations.¹² In a separate study, Corbin et al. noted enhanced postural control in adults who wore textured insoles featuring small rounded plastic nubs. Qiu et al. also documented reductions in postural sway among elderly participants when using either hard or soft insoles with small granulations on their surface, as did two related studies by Palluel et al. involving the use of sandals fitted with spike insoles.¹⁰

Conversely, Hatton et al. found no variation in static balance among older adults using either textured or smooth insoles. However, they noted a reduction in gait velocity with textured insoles, accompanied by smaller step and stride lengths compared to smooth insoles.¹³ Also, When investigating various foot orthoses such as cupped, textured, rigid, and soft insoles, Qu X found no discernible difference in static stability. Only the cupped insole demonstrated an enhancement in dynamic postural stability.¹⁴ All these studies had a small number of subjects, and balance analysis was performed immediately after the intervention.

Only two studies were conducted using textured insoles, but with a short follow-up period. In one of them, Perry et al. documented enhanced lateral stability during gait and a decrease in falls among 40 older adults living in the community following a 12-week protocol involving the use of a "facilitatory" insole with edge elevation.¹⁵ In contrast, Wilson et al. found no notable discrepancy in postural stability when investigating 40 healthy women (aged 51.1 ± 5.8 years) across four intervention groups (plain orthoses, dimple orthoses, grid orthoses, and a control group) during a four-week timeframe.¹⁶

Furthermore, it remains unclear whether the observed results would persist over extended follow-up periods. In this study, benefits were noted after eight weeks. Limited evidence of sustained balance improvement was found in other studies with follow-up periods ranging from 2 to 12 weeks.⁸

Conclusion

In the present investigation, improvements in the balance and postural control of subjects wearing customized or textured insoles were observed. These interventions may represent a cost effective and high-availability adjuvant methods for improving balance in the community-dwelling elderly people. The findings of our study hold significant implications in foot insoles research. The use of insoles for eight weeks resulted in a statistically significant improvement in balance, functional mobility, and pain. As no similar study was found in the literature, there is a clear need for further studies to determine the long-term benefits and effects of insoles in the older population. This study focused on a healthy and independent older adult population and research involving elderly population with multiple conditions is needed. No clear data is available regarding the optimal frequency of the insole use required to achieve balance sway improvement. As mentioned earlier, evident postural sway improvement was observed immediately following the intervention.

Conflict of Interest

Nil