EFFECT OF FOREFOOT TYPE ON POSTURAL STABILITY – A CROSS SECTIONAL COMPARATIVE STUDY

Abstract

Background and Purpose:

Weight‐bearing foot structure may influence postural control by either decreasing the base of support (BOS) or increasing the passive instability of the joints of the foot. Poor postural control has been implicated as the main causative factor for foot and ankle injuries. The purpose of this study was to examine the influence of forefoot postures on postural stability during single limb stance.

Methodology:

Sixty healthy individuals between the ages of 18 to 31 were selected using a purposive sampling procedure based on forefoot angle measurements and categorized into three groups; high forefoot varus (≥8°) (n=20), neutral forefoot varus (1°‐8°) (n=20) and low forefoot varus group (≤1°) (n=20). Static foot measurements, including relaxed rearfoot angle and navicular drop, and foot dimentsions were performed. Height and weight were also recorded for all the subjects. Center of Pressure (COP) excursion in Anterior‐posterior (AP) and Medial‐lateral (ML) planes and Stability Index (SI) with eyes open and eyes closed conditions were also measured using the force platform.

Results:

Strong correlations were found between forefoot angle and rearfoot angle (r=0.71, p<0.01), forefoot angle and navicular drop (r=0.58, p<0.01), and between rearfoot angle and navicular drop (r=0.661, p<0.01). There were no correlations (p>0.05) between the forefoot angle and all the five COP measures, except between forefoot angle and SI with eyes closed (r= ‐0.25 p<0.01).

Conclusion:

There is a significant positive correlation between forefoot angle and rearfoot angle and between forefoot angle and navicular drop. Forefoot angles did not affect the maximum AP COP and ML COP excursions or SI in healthy subjects.

Level of evidence:

3

INTRODUCTION

Postural control is the control of the body’s position in space for the purpose of balance and orientation.¹ Static postural control is the ability to stabilize or minimize the movement of the center of gravity within the base of support (BOS) when equilibrium status has been achieved for a given weight‐bearing position.^2-4 Human standing posture is maintained through a central postural mechanism assisted by sensory feedback from labyrinthine, visual, muscular and cutaneous origins that together contribute to postural stabilization as well as comprise the basis of a body posture representation.^5-7 The musculature of the legs, feet, and trunk use this feedback circuit, allowing the individual to stand erect against the forces of gravity.^8-11 Generally, to maintain an upright stance, the central and peripheral components of the nervous system are constantly interacting to control body alignment with the center of gravity within the base of support.^12-14 The proprioceptive system acts through the tactile senses of touch, pressure, and vibration and through the sense of position, which together help determine the relative positions and rates of movement of parts of the body.^8,11 Center of Pressure (COP) is defined as the point on the foot at which the body weight is equally distributed between the medial‐lateral (ML) and anterior‐posterior (AP) quadrants and is recorded in centimeters.¹⁵ Movement of the COP in the ML and AP directions reflects the body’s attempt to maintain postural control.^2-4 There is a positive correlation between poor postural control and risk of injury in athletic population.^16,17

The human foot serves to balance the individual directly or indirectly during a variety of static and dynamic activities such as standing, walking, running, swimming, and diving. During a static or dynamic stance, the foot is a “mobile adaptor” which provides optimal function with minimal risk of injury. The foot is the only direct source of contact with a supporting surface and therefore it plays an important role in all weight‐bearing tasks. When the components of foot effectively work together, it provides a balanced foundation for the body. Changes to foot structure, therefore, have the potential to alter the load distribution functions of the foot.¹⁸ Malalignments in the structures of the forefoot, midfoot, and rearfoot are thought to lead to compensatory motion,¹⁹ which may ultimately result in injury.²⁰ Structural and positional imbalances of the foot may contribute to overuse injuries throughout the kinetic chain.²¹ Furthermore, it is suggested that the forefoot should be normally aligned perpendicular to the bisection of the calcaneus when the foot is in subtalar joint neutral.²² The subtalar joint neutral position has been considered to be an important reference position from which motion can be measured.²³ Subtalar joint neutral position is defined as a navicular angle between 130° and 150°, a normal medial longitudinal arch, and a calcaneal position of perpendicular to the ground.²⁴ Any deviation from this position, either varus or valgus, is considered abnormal and could lead to abnormal motion and potential injury. However, recent studies have suggested that a certain variation in forefoot varus or valgus may be normal in an adult population.^25,26

A forefoot angle (FFA) measurement, usually performed in a non‐weight bearing position, ranging between 1‐8 degrees is considered neutral/normal and higher or lower than this range results in a description of high forefoot varus (i.e., ≥8˚) or low forefoot varus (i.e., ≤1˚).²⁷ If the FFA is more than 8˚ (or in the inverted position of the forefoot on the calcaneus), the midtarsal joints are completely pronated during weight‐bearing. This results in decreased osseous stability in the midtarsal joints and an inadequately rigid foot which leads to excessive hyper mobility of the subtalar joint and midtarsal joint during weight‐bearing.²² Previous authors have shown that abnormal foot posture, such as an excessive pronation, is a predisposing and/or causative factor for several foot and lower limb dysfunctions such as those that may lead to anterior cruciate ligament injury.²⁰ Likewise, when the FFA is <1˚ i.e., in everted position of the forefoot on the heel, the midtarsal joint is supinated and more of the lateral aspect of the foot is brought into contact with the ground²⁷ resulting in less plantar contact area.²⁸ This leads to reduced sensory input from plantar sensory end organs²⁵ thereby reducing sensory input that is important for controlling or maintaining balance.²⁹ Therefore, clinical assessment of foot posture may be an essential component for the management of any lower limb pain or dysfunction.

The influence of forefoot structure on weight‐bearing midfoot and rearfoot positions has not been extensively investigated. In addition, the influence of foot structure on postural control has not been well investigated. Thus, for the prevention of injuries, better understanding of the variables that influences postural stability may be useful. The objective of this study is to examine the influence of forefoot postures, (i.e., high, low and neutral forefoot types) on postural control during single limb stance, in both eyes closed and eyes open conditions. A secondary purpose was to investigate is the relationship between forefoot types, a person’s height, foot dimensions, and associated positions in the midfoot and rearfoot. It was hypothesized that types of forefoot postures would affect postural stability and there would be a significant relationship between static forefoot postures and the midfoot and rearfoot postures during stance.

METHDOLOGY

Participants

Sixty healthy subjects between the ages of 18 to 31 were selected using a purposive sampling procedure. One hundred and fifty four healthy volunteers were screened in order to enroll 60 subjects comprising three equal groups based on their forefront measurements in prone lying position. Male and female subjects who had no history of lower extremity injury or pain in the six months prior to participation, could follow commands, and had no diagnosis of any neural or vestibular disease or lower extremity arthritis were included in the study. Any subject who had engaged in exercise or training that might require good postural control ability (e.g., ballet and gymnastics) during the previous year were excluded from this study. Subjects who used substances which might affect postural stability (e.g., alcohol, sedatives, cold remedies, and stimulants) were also excluded. Also excluded were those subjects who had congenital or acquired musculoskeletal deformity. The institutional review board of the study center approved the testing procedures and all participating subjects signed an informed consents prior to their participation.

Procedure

For all participants, forefoot angles (FFA) in subtalar joint neutral position and in prone lying position were measured using standard measurement procedures (Figure 1).^27,30 The subjects were then divided into three groups with 20 subjects in each group, based on their FFA measurements. The groups were: High Forefoot Varus (HFV) group in which participants had varus greater than or equal to 8°, Neutral Forefoot Varus (NFV) group with varus between 1.0°‐ and 8.0° and Low Forefoot Varus (LFV) group with less than or equal to 1.0° varus.

Figure 1.

Forefoot angle measurement

Static foot measurements, were collected for all subjects including the Relaxed Rearfoot Angle (RFA) and the Navicular Drop (ND), which have been proven to be reliable and valid. Height and weight of each individual was also recored. All static measurements were performed by one investigator. The intra‐tester reliability was not assessed but has been reported to be good in similar studies.^27,32 A foot template for each subject was constructed to ensure the same foot placement for all standing measurement procedures. Each participant was asked to walk along a path of 4‐m length at his/her preferred speed and come to a stop on a 45cm × 60cm piece of paper. Subjects were asked to end their walks in a bilateral stance with both lower limbs in a foot placement angle that was most comfortable to them. Two practice trials were allowed and on the third trial, after the subject came to standstill, each foot was traced on the paper with a marker or ballpoint pen to make the foot template.²⁷ The length and width of each of the subjects’ feet from the foot templates were measured in centimeters (cms).³¹ (Figure 2) All subsequent standing measures were taken with the subjects standing on the foot template to ensure that the same foot placement was used for all the measures.

Figure 2.

Foot dimensions measurement on Foot Template

The ND is the difference in navicular height measured in millimeter (mm) during subtalar joint neutral and relaxed stance.^27,32 (Figure 3). The navicular height was measured in subtalar joint neutral and relaxed stance. Initially, the navicular bone of each foot was palpated when patient was sitting with feet supported and a mark was made with a marker on the most prominent aspect i.e., navicular tuberosity. Then, with the subject standing on a 6” wooden box, in his/her foot template, in bilateral stance, the subtalar joint in neutral position was palpated. An index card was placed vertically along the medial aspect of the foot and a mark was made on the card at the level of marked navicular. Each subject was asked to lift one foot off the box, bending the knee, and the navicular position was again checked on the index card during relaxed unilateral stance. The difference between these two measurements was utilized as the ND score.

Figure 3.

Navicular Drop measurement

For the Rearfoot Angle (RFA) measurement, first, longitudinal bisection lines were drawn with a marker along the posterior aspect of the lower third of the leg and the calcaneus for the bisection of the lower one‐third of the leg and the bisection of the calcaneus with the subject in prone. Then, the subject stood in his/her gait template, on the box, in unilateral stance. The relaxed RFA was measured as the angle between the bisection of the lower one‐third of the leg and the bisection of the calcaneus and measured in degrees (°)³² (Figure 4). All the standing measures were taken with subjects standing on the foot template to ensure that the same foot placement was used for all the measures. All the measurements were taken three times and an average of those measurements was used as the RFA score.

Figure 4.

Rear‐foot angle measurement

The balance ability of the each individual including max Center of Pressure (COP) excursions in AP and ML directions, and stability index (SI) was measured using a force platform which was supplied by Bertec^© Force Platform (Columbus, OH, USA). All the force platform measures for single leg stances were taken with participants standing barefoot on the force platform in two conditions, eyes open and eyes closed.¹⁵ All measurements were taken three times and averages were calculated. Each partiipanat performed three 10‐second trials of each condition. A longitudinal line was placed on the force platform in order to control the foot position during testing. The participants aligned the foot to be tested such a way that the longitudinal line bisected the calcaneus and the 1^st and 2^nd metatarsals.(Figure 5) The participants were then instructed to bend their non‐weight‐bearing limbs at the hips and knees and cross their arms over their chests. During the eyes‐closed condition, participants assumed the test position, closed their eyes, and gave verbal signals for their readiness. During testing the subjects were instructed to attempt to maintain their positions as motionless as possible without their non‐weight‐bearing limb touching either the ground or their weight‐bearing limb. They were also instructed to not use their arms for balancing. If balance was lost, the participants were instructed to resume the initial testing position as quickly as possible. When the non‐weight‐bearing limbs touched the ground, the score was excluded from data analysis.

Figure 5.

Force platform measurement procedure

Statistical Analysis

The data for all parameters were recorded on a data collection form and then converted to tabular form. Means, standard deviations, standard errors and Karl Pearson Product Moment Coefficients (r) were determined to examine the relationships between the static foot measures, foot dimensions, and the force plate measures in high, neutral and low forefoot varus groups. Separate one‐way analyses of variances (ANOVA) were used to investigate the differences in the static foot measures, COP excursions in AP and ML directions, and SI scores in single‐limb stance score among the three forefoot type groups. Multiple comparisons were performed using bonferroni post‐hoc corrections to test for significant differences between the three groups. Independent sample t‐tests were used to investigate the within‐subject variability in eyes open and eyes closed conditions within different forefoot varus groups. The level of significance was set at p0.05 for each analysis. All statistical analysis was performed using SPSS, version 20.0.

Results

Sufficient potential subjects were screened in order to reach a sample size of 20 participants in each group and maintain a 50% male and 50% female ratio. Some potential subjects who met the criteria for the neutral forefoot varus group were excluded from the study because a sufficient number of subjects had already been enrolled in this group.

Table 1 shows the descriptive statistics for baseline characteristics including age, height, weight and foot dimensions among the three groups. No significant differences (p>0.05) were found in terms of these baseline characteristics between the groups. This shows the homogeneity of the subjects among the groups on baseline characteristics. Table 2 shows the descriptive statistics for static foot angles and navicular drop (ND) among the three subgroups. Table 2 also shows the descriptive statistics for COP measures i.e., AP and ML excursion and SI in both eyes open and eyes closed conditions among the three subgroups. A significant difference (p<0.001) was found between RFA and ND measures between the groups. The values differed in all the pair‐wise comparisons between those three groups. However, no significant difference (p>0.05) were found in all of the force plate parameters among the groups.

Table 1.

Descriptive statistics for baseline characteristics among 3 forefoot subgroups.

Group	N	Male/Female	Age (year)	Height# (cm)	Weight(kg) #	Foot length (cm)#	Foot width (cm) #
HFV	20	10/10	20.7(1.45)	161(9.52)	59.86(11.84)	24.37(1.70)	9.68(0.78)
NFV	20	10/10	22.95(2.32)	164(10.2)	60.74(11.95)	24.72(1.68)	9.62(0.69)
LFV	20	10/10	20.4(1.56)	162(7.33)	54.48(7.45)	24.15(1.05)	9.46(0.75)

HFV= high forefoot varus; NFV= Neutral forefoot varus; LFV= Low forefoot varus

Values reported as Mean (SD), ^#‐ No significant difference (ANOVA) was found between the groups

Table 2.

Descriptive statistics for static foot angles and forceplate measurement parameters among 3 forefoot subgroups.

Group	N	FFA (°)	RFA* (°)	ND* (mm)	APSEO (cm) #	APSEC (cm) #	MLSEO (cm) #	MLSEC (cm) #	SIEO (%)#	SIEC (%)#
HFV	20	9.75 (1.05)	15.2 (2.38)	11.47 (1.72)	1.25 (0.3)	2.52 (0.99)	1.02 (0.31)	2.21 (0.17)	86.24 (2.93)	72.5 (10.02)
NFV	20	4.59 (1.87)	11.07 (1.80)	6.69 (1.52)	1.51 (0.72)	2.72 (1.68)	1.38 (0.76)	2.06 (0.67)	84.28 (4.43)	73.41 (8.32)
LFV	20	‐3.21 (1.94)	11.35 (2.65)	9.15 (2.54)	1.47 (0.51)	2.17 (0.5)	1.13 (0.42)	2.04 (0.6)	84.49 (4.09)	75.7 (4.79)

HFV= high forefoot varus; NFV= Neutral forefoot varus; LFV= Low forefoot varus

FFA= Forefoot angle; RFA= Rearfoot angle; ND= Navicular drop; APSEO= Anterior‐posterior stability eyes open; APSEC= Anterior‐posterior stability eyes closed; MLSEO= Medial‐lateral stability eyes open; MLSEC= Medial‐lateral stability eyes closed; SIEO= Stability index eyes open; SIEC= Stability index eyes closed.

Values reported as Mean (SD), *‐ Significant difference (ANOVA) was found between the groups, ^#‐No Significant difference (ANOVA) was found between the groups

Among the sixty subjects, relationships were analysed between the static forefoot angle, weight‐bearing midfoot position, height, weight, foot length, and foot width (Table 3). Results showed significant positive correlation between FFA and RFA (r=0.71, p=0.000) and between FFA and ND (r=0.58, p=0.000) (Figure 6), while there was a lack of correlation (p>0.05) between height (r=‐0.03), weight (r=0.17), foot length (r=0.04) and foot width (r=0.07). RFA had a significant positive correlation with ND (r=0.661, p=0.000) and a weak correlation with weight (r=0.30, p=0.03), while no correlations were found between height, weight and foot dimensions. Significant weak negative correlations (p<0.05) were found between FFA and SI eyes closed (r=‐0.25) and between RFA and SI eyes closed (r=‐0.26), while no correlations (p>0.05) were found between the foot angles and all other COP measures in both eyes open and eyes closed conditions, and SI in eyes open condition (Table 4).

Table 3.

Correlations between forefoot angle, foot measurement parameters and other variables among all the subjects.

Foot Angles	Pearson	Height (cm)	Weight (kg)	RFA (°)	ND (mm)	Foot Length(cm)	Foot Width (cm)
FFA (°)	r	‐0.03	0.17	0.71**	0.58**	‐0.04	0.07
	P level	0.85	0.20	0.000	0.000	0.77	0.6
RFA (°)	r	0.19	0.3*	1	0.66**	0.11	0.23
	P level	0.16	0.03	‐	0.000	0.41	0.08
ND (mm)	r	‐0.09	‐0.01	0.696**	1	‐0.087	0.102
	P level	0.51	0.93	0.000	‐	0.511	0.436
	N	60	60	60	60	60	60

FFA= Forefoot angle; RFA= Rearfoot angle; ND= Navicular drop

^**Correlation is significant at the 0.01 level.

^*Correlation is significant at the 0.05 level.

Figure 6.

Correlation between static foot angles and other foot measurements. :‐ mm – millimeters, Deg ‐ Degree

Table 4.

Correlation between forefoot angle and COP measures among all the subjects.

Foot Angles	Pearson	APSEO (cm)	APSEC (cm)	MLSEO (cm)	MLSEC (cm)	SIEO (%)	SIEC (%)
FFA (°)	r	‐0.07	0.23	‐0.04	0.217	0.065	‐0.25*
	P level	0.571	0.08	0.746	0.097	0.623	0.05
RFA (°)	r	‐.0.06	0.197	‐0.07	0.129	0.084	‐0.26*
	P level	0.96	0.132	0.557	0.324	0.524	0.043
ND (mm)	r	0.096	‐0.201	0.046	‐0.016	0.222	‐0.089
	P level	0.466	0.124	0.729	0.904	0.088	0.499
	N	60	60	60	60	60	60

FFA= Forefoot angle; RFA= Rearfoot angle; ND= Navicular drop; APSEO= Anterior‐posterior stability eyes open; APSEC= Anterior‐posterior stability eyes closed; MLSEO= Medial‐lateral stability eyes open; MLSEC= Medial‐lateral stability eyes closed; SIEO= Stability index eyes open; SIEC= Stability index eyes closed.

No significant differences were revealed within the high, neutral and low forefoot varus groups between mean values of AP COP excursion with both eyes open (F=1.483, p>0.05) and eyes closed (F=1.14, p>0.05) conditions. But, a significant within‐subject difference was found for eyes open versus eyes closed conditions in the high forefoot varus (p<0.001), in neutral forefoot varus (p<0.001) and low forefoot varus (p<0.001) groups. This is illustrated in Figure 7.

Figure 7.

Comparison of mean anterior‐posterior COP excursion between eyes open and closed condition within 3 forefoot groups. Cms – centimeters, COP ‐Center of Pressure

No significant differences were revealed in the mean values of ML COP excursion within the high, neutral and low forefoot varus groups in both eyes open (F=2.43, p>0.05) and eyes closed (F=0.32, p>0.05) conditions. But, a significant within‐subject difference was found for eyes open versus eyes closed conditions in the high forefoot varus (p<0.001), in neutral forefoot varus (p<0.001) and low forefoot varus (p<0.001) groups. This is illustrated in Figure 8.

Figure 8.

Comparison of mean medial‐lateral COP excursions between eyes open and closed condition within 3 forefoot groups. Cms – centimeters, COP ‐Center of Pressure

There were no significant differences in the SI (Figure 9) within the high, neutral and low forefoot varus groups in both eyes open (F=1.56, p>0.05) and eyes closed (F= 0.85, i.e., p>0.05) conditions. But, a significant within‐subject difference was found for eyes open versus eyes closed conditions in the high forefoot varus (p<0.001), neutral forefoot varus (p<0.001) and low forefoot varus (p<0.001) groups.

Figure 9.

Comparison of mean values of Stability Index between eyes open and closed condition within 3 forefoot groups. Cms – centimeters, SI – Stability Index

Discussion

The human foot provides the only direct contact with the supporting surface and therefore plays an important role in all weight‐bearing tasks. Changes in foot structure therefore have the potential to alter the load distribution function of the foot.¹⁸ It has been suggested that the forefoot should be aligned perpendicular to the bisection of the calcaneus when the foot was in subtalar joint neutral.²² Any deviation from this position could lead to varus and valgus forces which can lead to compensatory motions.¹⁹ Malalignments in the structure of the forefoot, midfoot, and rearfoot are thought to lead to compensatory motions,¹⁹ which ultimately may result in injury.^20,33 Therefore, clinical evaluation of foot posture may be useful for assessing and treating patients with lower extremity dysfunctions. This study, therefore, aims to find the influence of forefoot posture on postural control during single limb stance, in both eyes closed and open conditions. Also investigated was the relationship between forefoot types, foot dimensions and associated positions in the mid‐foot and rearfoot.

In this study sixty healthy subjects in the age group of 18 to 31 years were included. No significant difference was found in either height, weight, foot length and foot length between the three group subjects showed the homogeneity among the samples. Also gender did not play a role in the study due to equal distribution among the groups. It was assumed that there is a potential for data inflation when using measurements from both the right and left foot of the same individual.³⁴ Therefore, in order to respect the assumption of independence, the authors of the current study took data from one limb only, using a random selection procedure.

The relationship between FFA and relaxed RFA in stance is based on the principle that when a forefoot varus angle is present, the rearfoot will evert in order to bring the foot parallel to the ground.¹⁸ It was not known whether forefoot varus leads to midfoot/rearfoot pronation or if midfoot/rearfoot pronation over a long period of time creates a forefoot varus due to medial loading. Results of this study showed a positive correlation between the FFA and the RFA in relaxed stance (p<0.01). This is supported by a previous report, which also showed moderate correlation between forefoot angle and rearfoot angle (r = 0.52, p<0.001).²⁷This positive correlation shows that if one variable increases, there will likely be a compensatory increase in other variable meaning that forefoot varus has a significant relation to rearfoot eversion. Meanwhile, another report found no correlation between rearfoot and forefoot position (r = 0.00‐0.14).³⁵ The authors of that study also found significant difference (p<0.01) in RFA between the three forefoot groups. This contradictory finding may be because their measure of rearfoot angle in subtalar joint neutral did not take into account a possible pronation compensation while in the current study the rearfoot angle was measured in relaxed calcaneal stance.

While assessing the midfoot position, navicular drop provides an indication of midfoot pronation and if the forefoot alignment is within a neutral range, there may not be a need to compensate through the midfoot or rearfoot.²⁷ Therefore, this study sought to examine the relationship between forefoot angle and navicular drop. The significant positive correlation (r=0.58, p<0.001) found between forefoot angle and navicular drop confirmed the results of a previous study.²⁷ There was also a significant difference (p<0.01) found in ND between the three forefoot groups in the current study. But, the results found by another group of researchers did not show any significant correlation (r = 0.29, p>0.05).³⁵ A possible limitation in using navicular drop is the potential for skin movement over the marked navicular tuberosity. In the current study the navicular tuberosity position was marked in subtalar joint neutral and it was not marked again during standing relaxed position. This may have resulted in underestimation of the true excursion of the navicular drop.

Positive correlations (p <0.001) were found between rearfoot angle and navicular drop in all groups of subjects of the current study. Other researchers also found that navicular drop was a significant predictor of maximal rearfoot eversion.^32,35,27 McPoil and Cornwall found in an earlier study that among 17 static measures, only navicular drop substantially affected maximum rearfoot eversion angle.³² This means that higher navicular drop values were significantly associated with changes in rearfoot eversions. In other words, ND influences the rearfoot position.

Differences in postural control during single‐leg stance are typically examined either with side‐to‐side comparisons in unilaterally injured subjects^36,37 or between healthy and injured subjects.^38-40 Several studies have demonstrated no significant differences in postural control measures between the right and left limbs,^41-43 or dominant and non‐dominant limbs of healthy subjects in single‐leg stance.⁴⁴ A few researchers have examined the role of different foot postures on postural control.^15,19,31 The current study has included measurements of maximum COP excursions in AP and ML directions and SI as measures representing the reactions to accelerations of the centers of mass, and compared the effect of forefoot types on postural stability. No significant differences (p>0.05) were found in any of the COP and SI measurements between the three forefoot groups. It has been hypothesized that an excessively supinated or pronated foot posture may influence the somatosensory input via changes in joint mobility (hypo‐ or hyper mobility) or plantar foot surface contact area (excess or no arch) in order to maintain a stable base of support.³⁷ The lack of significant differences in postural measures between subjects of differing foot types might be explained compesatory balance strategies for each foot type.

The relationships between FFA and different COP measures (AP, ML, SI) with both eyes open and eyes closed conditions were analysed. The results of this study showed a weak negative correlation between forefoot angle and SI in eyes closed condition (r=‐0.25, p<0.05). Other than that, no correlations (p>0.05) were found between the forefoot angle and all other COP measures i.e., AP and ML COP excursions with both eyes open and eyes closed conditions, and in SI in eyes open condition. This indicates that different forefoot types by themselves were not associated with postural stability. This is likely due to the fact that postural control is a function of various systems, used together, in order to maintain postural stability or to maintain the center of gravity over the base of support. It is generally accepted that human standing posture is maintained through a central postural program assisted by various forms of sensory feedback such as labyrinthine, visual, muscular and cutaneous origin which together contribute to postural stabilization.^{9, 10, 46-48}

No significant differences in maximum AP excursions were found within the high, neutral and low forefoot varus group in both eyes open (p>0.05) and closed (p>0.05) conditions. Cobb et al showed that AP postural stability scores in the “more” forefoot varus (MFV) group are significantly higher than those of the “less” forefoot varus (LFV) group.⁴⁵ They used standard deviations of the x‐axis and y‐axis ground reaction forces for their measures of stablity, while the current study included maximum displacements in AP and ML directions and SI as stability measures. In their study, Cobb et al considered 7° as a reference value and divided subjects into HFV (FFA ≥ 7°) and LFV (FFA < 7°). Further, they only had 32 subjects who were not homogenously divided into two groups as compared to the current study where there were homogenous groups. In this current study, no significant interactions in maximum AP excursions and SI were observed within the high, neutral and low forefoot varus groups in both eyes open (p>0.05) and eyes closed (p>0.05) conditions. Cobb et al show that MFV group demonstrated greater ML stability scores compared to HFV group; however, this difference was not statistically significant.⁴⁵ This provides lack of support for the first hypothesis in the current study because different foot postures did not significantly affect the postural stability. It is also possible that the postural control system of the body may function to reduce the velocity and acceleration of the body mass more than absolute displacement which reduces the body sway. ⁴³ That might explain the lack of significant impact of foot postures on COP measures.

One of the limitations of the current study is that only healthy individuals were included while subjects with plantar heel pain, other diseases, and elderly persons were excluded. In addition, this study has analyzed only the static relationships between forefoot postures and associated positions but did not consider the relationships between different foot postures during dynamic activities. These dynamic postural relationships pertaining to functional activities could be subjects of further study as they may help in predicting the injury profiles of individuals.

CONCLUSION

This results of this study indicate that positive correlations existed between forefoot angle, rearfoot angle, and navicular drop in healthy subjects while forefoot angle had no relationship to the maximum AP and ML COP excursions and SI in both eyes open and eyes closed conditions. Finally, visual input had a significant effect on maximum AP and ML COP excursions and for SI irrespective of varied forefoot varus angles.