Comparing Medial Arch Supports with Different Rubber Densities for Adolescents with Flexible Pes Planus

Introduction

Human foot is a complex structure essential for posture and balance, enabling various activities like walking, running, and jumping.¹ Dysfunction, often resulting from an imbalance of forces supporting the arch, can lead to pes planus (flatfoot), where the medial longitudinal arch collapses, impacting daily activities.1 Flatfoot presents with varying deformities and symptoms, often called “fallen arches,” and can arise from factors like muscular imbalance, excess weight, or weakened support structures.²

Harris and Beath’s classification divides flatfoot into three types - flexible flatfoot (FFF), which is generally asymptomatic; flexible flatfoot with a short tendo-Achilles (FFF-STA), which often causes pain and functional disability; and peroneal spastic or rigid flatfoot, which is frequently symptomatic and associated with tarsal coalitions and reduced subtalar joint mobility.³ The importance of early identification and intervention in flatfoot cannot be overstated. For instance, the calcaneonavicular coalition and talocalcaneal coalition, often associated with rigid flatfoot, are usually completed around the ages of 14 to 16 years.⁴

Treating flat feet is crucial for reducing symptoms like foot pain and preventing conditions like knee and hip osteoarthritis. Orthotic intervention, especially arch-support orthoses, help by realigning the foot bones and redistributing weight to ease pain in the feet, knees, hips, and lower back. Studies have shown that custom arch supports can improve gait and increase range of motion.⁵ A study conducted by Sathish K Paul observed that microcellular rubber (MCR) displayed the highest level of deformation compared to other materials, making it an ideal choice for effectively dissipating peak plantar pressures within footwear. The elastic deformability of these materials, characterized by linear stress and strain until reaching the yield point, means that increased deformation results in more significant insole displacement.⁶ However, research on the effect of MCR Shore hardness on medial arch support for flexible pes planus is limited. 

This study sought to address this gap by investigating the effectiveness of medial arch supports made from MCR with different Shore hardness levels in adolescents with flexible pes planus. By employing specific foot assessment tests such as the Navicular Drop Test (NDT) and Plantar Pressure assessment using tools like the Harris Foot Mat, this research aimed to provide evidencebased insights into the optimal level of support required to manage flat feet effectively in this population.^7,8 The findings are expected to have significant implications for orthotists, enabling them to choose appropriate materials based on individual patient needs, thereby optimizing foot biomechanics and

promoting overall foot health.

Materials & Methods

This experimental study was conducted to evaluate the effectiveness of two different Shore hardness values of microcellular rubber (MCR) medial arch supports in treating flexible pes planus in adolescents. The study was carried out from December 2023 to May 2024 at two schools in Bhopal: Kempfort Public School and M.G.M. Co-ed. HR. Sec. School. Ethical approval for the study was obtained from the Institutional Ethical Review Board of Mobility India Rehabilitation Research and Training Centre, Bengaluru, India, under application number MI/IERB/006/2023. The study was conducted in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki.

Study Design

The study employed a randomized pre-test and post-test design over a period of four weeks.⁹ Participants were randomly assigned to either an experimental or control group to assess the effectiveness of different Shore hardness values of MCR medial arch supports. The experimental group received Shore 20 MCR arch supports, while the control group received Shore 15 MCR arch supports as shown in Figure 1.

Participants

The study targeted adolescents aged 14 to 16 years who were diagnosed with flexible pes planus. The inclusion criteria encompassed adolescents with mild to moderate flexible pes planus, as identified by clinical examination. Exclusion criteria involved individuals who had undergone recent foot surgery, had severe flat feet, experienced pain or instability affecting foot function, or had cognitive impairments that might affect their ability to comply with the study protocol. A total of 30 participants were recruited and randomly divided into two groups, with 15 participants in each group.

Sampling and Randomization

Participants were selected using simple random sampling to minimize selection bias and ensure that each eligible individual had an equal chance of being included in the study. Randomization was carried out using Microsoft Excel’s random number generation function, which randomly assigned participants to either the experimental group or the control group.

Sample Size Calculation

To estimate the sample size for this comparative study on the effectiveness of medial arch supports with different hore hardness values (15˚A and 20˚A) for adolescents with flexible pes planus, the following parameters were considered:

The sample size (N) was calculated using the following formula:¹⁰

• Minimum detectable difference (d): 6.0
• Pooled standard deviation (σ): 6.56
• Type I error (α): 5%
• Type II error (β): 10% (90% power)
• Zα=1.96, Z1−β=1.28

Substituting the values into the formula:

1. Calculate the sum of Zα+Z1−β:Zα+Z1−β = 1.96+1.28 = 3.24
2. Square the sum: (3.24)² = 10.4976
3. Square the pooled standard deviation (σ): (6.56)² = 43.0336
4. Multiply the squared terms: 10.4976×43.0336 = 451.729810.4976
5. Square the minimum detectable difference (d): d2 = (6.0)²=36
6. Calculate the sample size (N): N = 451.7298 ÷ 36 ≈ 12.55

Thus, the required sample size was estimated to be 13 participants per group, totalling 26 participants. However, to ensure robustness and account for potential dropouts, 30 participants were recruited, with 15 participants in each group.

Intervention Procedure

1. Screening and Consent: All potential participants were screened for eligibility, and informed consent was obtained from their parents or guardians before their inclusion in the study.
2. Baseline Assessment: To establish pre-intervention data, baseline measurements of foot posture, plantar pressure distribution, and medial longitudinal arch height were collected using the Navicular Drop Test (NDT) and a Harris foot mat.
3. Fabrication of Arch Supports: Customized medial arch supports were fabricated for each participant using MCR material with two different Shore hardness values (15 and 20), as shown in Figure 1. The supports were tailored based on foot tracings to ensure a proper fit.
4. Intervention: Participants in both groups were instructed to wear the assigned arch supports daily for four weeks. Proper usage and care instructions were provided to ensure compliance.
5. Post-Intervention Assessment: After the four-week intervention period, post-intervention assessments were conducted using the same tools to measure changes in foot posture, plantar pressure distribution, and arch height.

Outcome Measures

The study employed two primary outcome measures:

Navicular Drop Test (NDT): The NDT was used to assess the change in the height of the navicular bone between weight-bearing and non-weight-bearing conditions, which is indicative of the function of the medial longitudinal arch. A positive change would indicate an improvement in arch height and function.⁷

Plantar Pressure Analysis: Plantar pressure distribution was evaluated using a Harris foot mat, which provides a visual and quantitative assessment of pressure points on the foot. This method categorizes foot imprints by arch height and pressure distribution, with the goal of observing a more even distribution post-intervention.⁸

Data Analysis

The statistical software, namely SPSS 22.0 and environment ver.3.2.2, were used to analyze the data, and Microsoft Word and Excel were used to generate graphs, tables, etc.¹¹ Descriptive statistics were used to summarize the demographic data of the participants.

Independent t-tests were conducted to compare pre- and post-intervention outcomes between the experimental and control groups. A P-value of <0.05 was considered statistically significant.

Results

The study aimed to evaluate the effectiveness of medial arch supports with different Shore hardness values (15˚A and 20˚A) in improving the medial longitudinal arch height and reducing plantar pressures in adolescents with flexible pes planus.

Demographic Data

The participants were evenly distributed across the two groups, with 15 participants each in the control group (Shore 15˚A) and the experimental group (Shore 20˚A). The mean age of participants was 15 years (SD ± 0.75), with no significant difference in age between the groups (P=1.00).

Age Distribution: The mean age of participants in both groups was 15 years, with a standard deviation of ± 0.75. The age distribution was consistent between the two groups, ensuring that age-related variables did not confound the results.

Gender Distribution: In the control group, 40% of the participants were female (n=6), and 60% were male (n=9). In the experimental group, 86.7% of participants were female (n=13), and 13.3% were male (n=2). This distribution suggests a higher proportion of females in the experimental group, which could be considered when interpreting results.

Baseline Characteristics: Both groups were similar in terms of height and weight, with no statistically significant differences between them, as shown in Figures 2 and 3. This homogeneity in baseline characteristics indicates that the two groups were comparable at the start of the intervention.

Navicular Drop Test (NDT) Score Analysis

The NDT scores quantitatively measured the medial longitudinal arch height and its functional integrity. Both groups showed significant improvement in NDT scores from pre- to post-intervention, with P-values <0.001 for the control group and 0.08 for the experimental group.

Control Group (Shore 15˚A): The NDT scores indicated a significant improvement in arch height following the intervention. The mean pre-intervention NDT score was 8.53±1.7, and the post-intervention score improved to 4.6±3.5, reflecting a statistically significant change (P <0.001).

Experimental Group (Shore 20˚A): Similarly, the experimental group demonstrated a notable improvement in NDT scores, with the mean pre-intervention score being 8.33±3.63 and the post-intervention score improving to 4.93±2.81. Although the improvement was substantial, the P-value of 0.08 suggests a trend towards significance, indicating that further investigation with a larger sample size might be warranted to fully understand the effects as shown in Table 1.

Plantar Pressure (PP) Analysis

Plantar pressure analysis was conducted under static and dynamic conditions to assess the effectiveness of the medial arch supports in redistributing plantar loads.

Static PP: Pre-intervention mean PP Static scores were 1.33 ± 0.89 for control group (Shore 15) and 1.66 ± 0.97 for experimental group (Shore 20), with a total mean of 1.50 ± 0.93. The P-value for pre-intervention scores was 0.862, indicating no significant difference between the two groups before intervention.

Post-intervention mean PP Static scores were 0.53 ± 0.51 for control group (Shore 15) and 0.60 ± 0.51 for experimental group (Shore 20), with a total mean of 0.57 ± 0.504. The P-value for post-intervention scores was 1.000, suggesting no significant difference between the two groups after intervention (Table 2).

Dynamic PP: Pre-intervention mean PP Dynamic scores were 1.00 ± 0.92 for control group (Shore 15) and 2.07 ± 0.798 for experimental group (Shore 20), with a total mean of 1.53 ± 1.008. The P-value for pre-intervention scores was 0.002, indicating a significant difference between the two groups before intervention.

Post-intervention mean PP Dynamic scores were 0.53 ± 0.51 for control group (Shore 15) and 0.67 ± 0.61 for experimental group (Shore 20), with a total mean of 0.60 ± 0.56. The P-value for post-intervention scores was 0.526, suggesting no significant difference between the two groups after intervention (Table 3).

Discussion

The objective of this study was to investigate the impact of medial arch supports made from microcellular rubber (MCR) with different Shore hardness levels (15˚A and 20˚A) on adolescents with flexible pes planus. By focusing on this specific population, the study aimed to provide insights into the optimal level of support required to manage flexible flatfoot, a condition that can lead to discomfort and long-term complications if left untreated.

The study’s findings indicate that both Shore 15 and Shore 20 MCR medial arch supports were effective in improving the medial longitudinal arch height, as evidenced by significant improvements in Navicular Drop Test (NDT) scores. Additionally, both types of supports contributed to a more even distribution of plantar pressures, as shown by the results of the plantar pressure analysis. These outcomes suggest that medial arch supports with Shore hardness values of 15˚A and 20˚A can both be used effectively to manage flexible pes planus in adolescents, with each providing specific benefits.

Comparison with Existing Literature 

The findings of this study are consistent with previous research that highlighted the importance of arch support in managing flat feet. For instance, studies by Su et al., (2017) have shown that the hardness and design of orthotic materials significantly impact plantar pressure distribution and the correction of arch height.¹² The slight differences observed between the two Shore hardness levels in this study suggest that while both are effective, Shore 20 may provide marginally better support in static conditions, whereas Shore 15 might offer greater comfort.

A notable aspect of this study is its focus on adolescents, a population that has been underrepresented in the literature. Adolescents are at a critical stage of development, where the structure and function of the foot are still evolving. This makes early intervention crucial to prevent the progression of flatfoot and the associated complications. By investigating the effectiveness of medial arch supports with different Shore hardness values in this age group, this study provides valuable insights that can inform clinical practice and guide the development of orthotic interventions tailored to the needs of adolescents with flexible pes planus.

Clinical Implications

The study’s results have several important clinical implications. First, the findings support the use of medial arch supports as an effective intervention for managing flexible pes planus in adolescents. Orthotists and clinicians can consider using MCR medial arch supports with Shore hardness values of 15˚A or 20˚A, depending on the specific needs and preferences of the patient. For instance, patients who prioritize comfort may benefit more from Shore 15 supports, while those who require greater structural support may find Shore 20 more suitable.

Second, the study highlights the importance of customizing orthotic interventions based on the individual characteristics of the patient. Given that both Shore 15 and Shore 20 supports were effective, the choice of material can be guided by factors such as the severity of the flatfoot, the level of physical activity, and the patient’s overall foot biomechanics. This personalized approach can help optimize the outcomes of orthotic interventions and improve the quality of life for adolescents with flexible pes planus.

Limitations

Despite its strengths, this study has several limitations that must be acknowledged. One limitation is the relatively small sample size, which may limit the generalizability of the findings. While the study was adequately powered to detect significant differences between the two groups, a larger sample size would provide more robust results and allow for a more detailed analysis of subgroups, such as differences between males and females.

Another limitation is the short duration of the follow-up period. The study assessed the effectiveness of the medial arch supports over a period of four weeks, which provides valuable insights into their short-term impact but does not capture the long-term outcomes of using these supports. Future studies should include longer follow-up periods to assess the durability of the improvements observed and to determine whether the benefits of the intervention are sustained over time.

Lastly, the study focused exclusively on adolescents with flexible pes planus, which limits the applicability of the findings to other populations, such as adults or individuals with rigid flatfoot. While the results are relevant to the target population, further research is needed to explore the effectiveness of medial arch supports with different Shore hardness values in other groups.

Future Scope 

This study opens several avenues for future research. One potential direction is to conduct longitudinal studies that follow participants over an extended period to assess the long-term effectiveness of medial arch supports. Such studies would provide valuable information on the durability of the intervention and its impact on preventing the progression of flexible pes planus into more severe forms of flatfoot.

Another area for future research is to investigate the effectiveness of medial arch supports in other populations, such as adults or individuals with rigid flatfoot. By comparing the outcomes of different Shore hardness values in these groups, researchers can develop a more comprehensive understanding of how to tailor orthotic interventions to meet the needs of diverse populations.

Additionally, future studies could explore the combination of medial arch supports with other interventions, such as physical therapy or strength training, to determine whether a multimodal approach offers additional benefits for individuals with flexible pes planus. This holistic approach could lead to the development of more comprehensive treatment protocols that address the multifactorial nature of flatfoot.

Conclusion

In conclusion, this study demonstrates the effectiveness of medial arch supports made from microcellular rubber (MCR) with different Shore hardness levels in improving foot biomechanics and reducing plantar pressures in adolescents with flexible pes planus. Both Shore 15˚A and 20˚A supports were found to be effective, with each providing specific benefits that can inform clinical decision-making. The findings of this study have important implications for the management of flexible pes planus in adolescents, highlighting the value of personalized orthotic interventions that consider the unique characteristics and needs of the patient. While further research is needed to explore the long-term outcomes and effectiveness in other populations, this study provides a solid foundation for understanding the role of medial arch supports in managing flexible flatfoot and improving the quality of life for affected individuals.

Conflicts of Interest

The authors declare no conflicts on interest regardiing this manuscript.