Impact of Arch Height Flexibility on Dynamic Plantar Pressure in Healthy Young Subjects with Planus Feet

INTRODUCTION

Healthy feet are important for health and well-being. Previous studies of 2,994 subjects (65.5 y) showed that those with pes planus had an increased odds of having foot deformities, hyperpronation in gait, and lower outcomes.[1]

The investigators assessed foot structure, function, and arch height flexibility (AHF) in 1, 090 cadets of the USMA who volunteered for the study at the beginning of basic training. Prevalence of pes planus, based on standing arch height index (AHI), was 73.4% overall [2]. Planus feet demonstrated greater AHF, hyper-pronation (reduced center of pressure excursion index, CPEI), and smaller foot elongation compared to rectus and cavus foot types, see Table 1. Flexible feet displayed a significantly greater pronatory foot posture (lower AHI), greater flexibility (larger foot elongation), and greater amount of pronation in gait (lower CPEI) than those feet with referent and stiff arches.

The purpose of this study was to elucidate the complex relationship between foot function and flexibility while controlling for foot structure.

Table 1. Comparsion across 3 foot types.

Table 1. Comparsion across 3 foot types.

Figure 1. A sample dynamic plantar pressure for the planus, rectus, and cavus foot types are shown from left to right.

Figure 1. A sample dynamic plantar pressure for the planus, rectus, and cavus foot types are shown from left to right.

METHODS

Of the 1,090 USMA cadets (172 female, 18.5 ± 1.1 years, 24.5 ± 3.0 kg/m2 ), 1,414 planus feet were included in the analysis.

AHI (arch height at half the foot length / truncated foot length) and AHF (arch drop from sitting to standing in mm/40% of body weight in kN) were measured using arch height index measurement system (AHIMS, JAK Tool, Cranbury Township). AHF is stratified into 3 categories: largest quintile as flexible, middle 3 quintiles as referent, and smallest quintile as stiff. Gross foot structure was categorized into one of three foot types (planus, rectus, and cavus), based on the standing arch height index (AHI)[2].

Dynamic foot function was assessed using emed-X (novel GmbH, Munich) with 4 sensors/cm² at 100 Hz, utilizing the two-step method during comfortablepace walking. Five trials of barefoot dynamic plantar pressure were obtained for each foot The Center of Pressure Excursion Index (CPEI, %) and Peak Pressure (PP, kPA) were calculated for each trial.

Generalized Linear Model with an identify link function was used to examine the effects of AHF category while accounting for potential dependence in bilateral data. The Wald Chi-square was calculated for each dependent variable with significance set at p < 0.05. Post hoc pairwise comparisons for all pairs were performed using the Generalized Chi Square test at P < 0.05.

Figure 1. Arch height index (AHI) and arch height flexibility (AHF) were measured using the AHIMS (left). Dynamic plantar pressure was measured using novel emed-X system while subjects walked at self-selected comfortable speed (right). CPEI was used to quantify the plantar loading profile of each footprint; reduced CPEI is associated with hyper-pronation.

Figure 1. Arch height index (AHI) and arch height flexibility (AHF) were measured using the AHIMS (left). Dynamic plantar pressure was measured using novel emed-X system while subjects walked at self-selected comfortable speed (right). CPEI was used to quantify the plantar loading profile of each footprint; reduced CPEI is associated with hyper-pronation.

RESULTS

Those subjects with planus foot type with increased arch flexibility showed greater hyperpronation (reduced CPEI) while those planus feet with increased stiffness showed increased peak pressure in gait.

Table 2. Comparsion across 3 AHF categories in subjects with pes.

Table 2. Comparsion across 3 AHF categories in subjects with pes.

DISCUSSION

A significant difference (P<0.05) was shown in CPEI and PP. Results suggest that, in addition to foot structure (AHI), the arch flexibility may affect dynamic foot function.

This study includes a comprehensive measure of foot structure, function, and flexibility in a large sample of healthy active young subjects.

Lower extremity overuse injuries are common and costly problem. About a third of all (55.6% of female) USMA cadets experienced a lower extremity musculoskeletal injury by the end of their first year of training.

Identifying potentially modifiable risk factors for subsequent lower extremity injury incidence, based on a set of comprehensive measures of foot as well injury history, is expected to assist in the development of effective injury preventive measures.