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Journal of Back and Musculoskeletal Rehabilitation 28 (2015) 629–633 DOI 10.3233/BMR-130449 IOS Press
Comparison of plantar pressure between flat and normal feet when crossing an obstacle at different heights Jin-Tae Hana , Jung-Hoon Leeb,∗, Eun-Ju Leec, Chang-Hun Limd and Won-Bok Kime a
Department of Physical Therapy, College of Science, Kyungsung University, Busan, Korea Department of Physical Therapy, College of Nursing and Healthcare Sciences, Dong-Eui University, Busan, Korea c Department of Physical Therapy, Busan ST. Marrys Medical Center, Busan, Korea d Department of Physical Therapy, Gangneung Yeongdong College, Gangneung, Korea e Department of Physical Therapy, Daegu University, Daegu, Korea b
Abstract. OBJECTIVE: The purpose of this study is to compare the plantar foot pressure and the center of pressure (COP) pathway of normal and flat feet while crossing an obstacle at different heights. METHODS: Nineteen subjects (10 normal feet, 9 flat feet) participated in this study. The plantar foot surface was divided into the following seven regions for pressure measurement: two toe regions, three forefoot regions, one midfoot region, and one heel region. A one-way ANOVA with repeated measurements was used to compare the plantar foot pressure of normal and flat feet according to the obstacle height. RESULTS: The trend analysis showed a quadratic trend during level walking for the normal foot group, but a linear trend appeared as the obstacle height increased. In the flat foot group, the trend analysis showed a linear trend regardless of the obstacle height. In the 2nd-3rd metatarsal head region, the plantar pressure of the flat foot group increased more than the normal foot group as the obstacle height increased; however, in the 4th-5th metatarsal head region, the plantar pressure in flat feet was lower than in normal feet. In the heel region, the plantar pressure in both groups generally increased as the obstacle height increased, but the plantar pressure in the flat foot group was lower than in the normal foot group. CONCLUSION: We believe that, due to a loss of longitudinal arch, the COP path and plantar pressure of flat feet may be different from normal feet when crossing obstacles of different heights. Keywords: Plantar pressure, obstacle, flat foot, pathway of COP
1. Introduction The foot provides the interaction between the body and the ground. It also serves as a controllable mechanism and rigid lever [1]. However, flat feet make these ∗ Corresponding author: Jung-Hoon Lee, Department of Physical Therapy, College of Nursing and Healthcare Sciences, Dong-Eui University, 176, Eomgwangno, Busanjin-gu, Busan, 614-714, Korea. Tel.: +82 51 890 4222; Fax: +82 51 890 4229; E-mail: dreampt@ hanmail.net.
functions difficult. A flat foot is defined as a foot with an absent or abnormally low longitudinal arch height and pronation [2,3]. People with a low arch may be at an increased risk of metatarsal stress fractures [4]. Flat feet may also be responsible for the following: ligament laxity, muscle fatigue, foot/ankle instability, and valgus hindfoot due to inappropriate plantar loading [5,6]. Stepping over an obstacle is particularly associated with a shift in the center of mass closer to the supporting edge and large inertial forces, which threatens balance [7].
c 2015 – IOS Press and the authors. All rights reserved ISSN 1053-8127/15/$35.00
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J.-T. Han et al. / Comparison of plantar pressure between flat and normal feet
Stepping over an obstacle is very demanding and poses great risk when the foot’s motor function is poor [8]. When crossing obstacles, the plantar pressure is consistently modified and varies more at different obstacle heights. Plantar pressure can provide information about the foot loading changes with obstacles [9,10]. In some previous studies, the plantar pressure of normal and flat feet was compared [6,11,12], but most studies examined the differences only when walking on an even surface. In addition, few studies have quantitatively characterized the plantar foot pressure and the pathway of COP while crossing obstacles at different heights. Therefore, the aim of this study was to investigate the differences between flat and normal feet in plantar pressure and the COP pathway when crossing obstacles at different heights. It was hypothesized that the plantar pressure and pathway of COP would be modified in people with flat feet when crossing obstacles and that these factors may change more when crossing at different heights.
2. Materials and methods 2.1. Subjects Nineteen subjects (10 normal feet, 8 flat feet) participated in this study and were divided into two groups, one with flat and one with normal feet. Subjects were excluded for having musculoskeletal or neurological problems that would hinder a normal stance (e.g., osteoarthritis, ankle/foot deformities, nerve deficits, or brain injury). Prior to the start of the study the subjects signed an informed-consent document. 2.2. Navicular height and rear foot angle Each subject’s feet were marked at the following bony landmarks: the navicular tuberosity, the midline of the posterior calcaneal tuberosity, and the midline of the Achilles tendon [13]. We measured the navicular height and the rear foot angle of subjects with a measuring tape line and goniometer, respectively. The navicular height was defined as the height between the floor and the navicular tuberosity [14]. The rear foot angle was defined as the angle between the midcalcaneal line and the mid-Achilles line [6]. Subjects with a navicular height of less than 37 mm and a rear foot angle of more than 6◦ were considered to have flat feet [15].
Table 1 Common characteristics of subjects (Mean ± SD) Variables Normal feet (n = 10) Flat feet (n = 8) Age 20.60 ± 0.70 21.13 ± 1.64 Height (cm) 164.60 ± 9.71 165.38 ± 6.80 Weight (kg) 55.53 ± 9.11 58.75 ± 8.65 Foot sides (cm) 247.50 ± 14.58 246.88 ± 14.13 Navicular height (cm) 4.17 ± 0.31 2.80 ± 0.21∗ Rear foot angle (◦ ) 2.48 ± 0.79 6.27 ± 0.35∗ SD: Standard deviation. ∗ Significant difference (p < 0.05) between normal and flat feet.
2.3. Plantar foot pressure Plantar foot pressure data were recorded using the Matscan system (Tekscan, USA). The pressure sensor width was 702.579 mm, and the sensors were composed of a 44 × 52 matrix. The pressure distribution data were collected at 60 frames per second using the Tekscan Pressure Measurement System, Version 5.23 to analyze plantar foot pressure. Although a complex ad hoc calibration was necessary, Tekscan had a high accuracy [16]. For the pressure measurement, the foot was divided into the following seven plantar regions: two toe regions, three forefoot regions, one midfoot region, and one heel region [17]. The toe region was subdivided into two regions (i.e., the hallux and the lesser toes). The three forefoot regions underneath the metatarsal heads were subdivided into equal thirds. The medial forefoot region was underneath the first metatarsal head, the central region was underneath the second and third metatarsal heads, and the lateral region was underneath the fourth and fifth metatarsal heads. 2.4. Procedure All subjects were asked to pass the right foot above the Matscan while crossing the obstacles at different heights with bare feet. All trials were performed twice, and the average of both trials was used to analyze the data. The plantar pressures were measured, and the COP trends were found. 2.5. Statistical analysis In this study, the pressure and the pathway of COP were measured in subjects with normal and flat feet when crossing obstacles at different heights. A simple regression was used to estimate the pathway of COP between normal and flat feet during obstacle crossing with different heights. The curve trend was analyzed using the COP pathway from the heel to forefoot. We
J.-T. Han et al. / Comparison of plantar pressure between flat and normal feet
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Table 2 Comparison between normal and flat feet in the plantar foot pressure at seven plantar foot areas when crossing obstacles at different heights (Mean ± SD) Plantar foot area Hallux Lesser toe 1st MPJ 2–3 MPJ 4–5 MPJ Midfoot Heel
No obstacle Normal Flat 212.26 ± 101.75 251.75 ± 70.11 64.62 ± 26.79 70.05 ± 28.17 165.28 ± 77.48 165.39 ± 35.31 268.80 ± 40.29 310.28 ± 84.92 127.33 ± 45.64 78.39 ± 29.99 50.82 ± 32.93 61.68 ± 41.93 248.37 ± 37.85 198.21 ± 32.91
10 cm obstacle Normal Flat 229.03 ± 98.97 306.94 ± 81.96 66.43 ± 25.12 98.48 ± 47.41 164.35 ± 103.25 144.74 ± 41.67 268.45 ± 59.51 298.66 ± 74.69 116.03 ± 40.60 67.32 ± 12.33∗ 48.87 ± 35.13 62.28 ± 30.51 282.44 ± 52.20† 214.59 ± 44.62∗
20 cm obstacle Normal Flat 226.85 ± 89.28 299.81 ± 79.23 59.90 ± 17.88 97.33 ± 37.78∗‡ 163.32 ± 55.78 154.74 ± 29.22 287.58 ± 80.99 346.19 ± 88.52‡# 134.18 ± 63.06 78.69 ± 22.35∗ # 72.80 ± 42.12 60.22 ± 38.92 278.85 ± 49.60‡ 219.05 ± 48.85∗
Unit: kPa, SD: Standard deviations. ∗ Significant difference (p < 0.05) between normal and flat feet, † Significant difference (p < 0.05) between no obstacle and 10 cm obstacle, ‡ Significant difference (p < 0.05) between no obstacle and 20 cm obstacle, # Significant difference (p < 0.05) between 10 cm obstacle and 20 cm obstacle.
Fig. 1. Comparison of the COP pathway between normal and flat feet when crossing obstacles at different heights.
used a one-way ANOVA with repeated measurements to compare the differences in the plantar pressure by obstacle height in the normal and flat feet groups. An alpha level of 0.05 was used to test for significance. All data were analyzed using the SPSS 18.0 statistical software.
3. Results Table 1 shows the characteristics of the subjects who were divided into the normal and flat feet groups. Figure 1 represents the COP pathway of the normal and flat feet groups when crossing obstacles at different heights. The trend analysis showed a quadratic trend of COP during level walking for the normal feet group (R2 = 0.032), but a linear trend appeared as the obstacle heights increased (10 cm: R2 = 0.225, 20 cm: R2 = 0.587). However, for the flat feet group, the trend analysis showed a linear trend regardless of the obstacle
height (0 cm: R2 = 0.994, 10 cm: R2 = 0.930, 20 cm: R2 = 0.946). There is a linear trend as R2 moves closer to 1. Table 2 compares the plantar pressure in each foot region when stepping over obstacles at different heights. In the hallux and the lesser toe region, the planar pressure in the flat feet group was higher than that of the normal feet group during level walking and obstacle crossing and increased as obstacle height increased. In the lesser toe region, there was a significant difference between the normal and flat feet group at 20 cm obstacle and there was statistically significant difference by obstacle height at flat feet group. However, the plantar pressure of the flat foot group in the 1st metatarsal head region was lower than the normal foot group and decreased as the obstacle height increased and there was also no difference between the normal and flat feet group. In the 2nd –3rd metatarsal head region, the plantar pressure in the flat foot group significantly increased as obstacle
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J.-T. Han et al. / Comparison of plantar pressure between flat and normal feet
height increased (p < 0.05), but there was no statistically significant difference between the normal and flat foot groups (Table 2). In the 4th –5th metatarsal head region, plantar pressure in the normal foot group increased, but that of the flat feet group decreased. There was no difference in plantar pressure with obstacle height, but plantar pressure of the flat foot group was significantly lower than the normal foot group (p < 0.05). In the midfoot region, there was no difference in plantar pressure between the normal and flat foot group; however, the plantar pressure of the normal foot group when crossing obstacles was higher than that of the flat foot group and there was significantly increased at 20 cm height obstacle (p < 0.05) (Table 2). In the heel region, the plantar pressure increased as the obstacle height increased, and the plantar pressure of the flat foot group was significantly lower than that of the normal foot group (p < 0.05) (Table 2).
4. Discussion The results of this study showed that the pathway of COP in the normal feet group showed a quadratic trend while walking on an even surface and showed a linear trend as the obstacle height increased but that of the flat foot group showed a linear trend regardless of obstacle height. Additionally, the plantar pressure of the 2nd – 3rd metatarsal head and heel regions increased in both the normal and flat foot groups as the obstacle height increased. The plantar pressure of the 4–5th metatarsal head regions of the normal foot groups increased as the obstacle height increased but that of the flat feet group decreased. There was a significant difference between the normal and flat foot groups when obstacles crossing. The COP pathway in normal subjects begins at the heel and ends at the hallux and slightly shifts medially in the forefoot when walking on even surfaces [17,18]. The results of our study agree with previous studies of walking on level ground, and the difference between normal and flat foot groups are understood [6]. However, as the obstacle height increases, the COP path was shorter and straighter in flat feet as compared to normal feet. The results of our study agree with the previous literature that reported that the plantar pressure of flat feet was commonly higher than that of normal feet. In our study, the plantar pressure of the hallux and 2nd –3rd metatarsal head was higher in flat feet than normal feet and increased as the obstacle height increased. A few studies reported that plantar loading
beneath the midfoot was higher in flat feet than normal feet6 and that this increase in foot loading is due to a different foot type during walking [6,11,12]. However, the plantar pressure of the midfoot and heel regions as obstacle height increased was lower in flat feet than normal feet in our study. This finding indicates that the center of mass was more concentrated in the forefoot than the rearfoot for the propulsive force to step over the obstacle; therefore, we agree that the center of mass in flat feet shifts medially because of a loss in the foot arch [19]. This study was conducted to determine the plantar pressure and the COP pathway in subjects with normal and flat feet when crossing obstacles at different heights. The COP pathway of the normal feet group showed a quadratic trend when walking on an even surface and a linear trend as the obstacle height increased. However, the COP pathway in the flat feet group showed a linear pathway without regard to the obstacle height. In the 2nd –3rd metatarsal heads and the heel region, the plantar pressure increased as the obstacle height increased in both the normal and flat foot groups. The pressure of the 4th –5th metatarsal head regions of the normal foot group increased but that of the flat feet group decreased. This shows that the center of mass normally transfers forward and laterally as the obstacle height increases, but the flat foot group was already shifted medially due to a loss of the longitudinal arch. In conclusion, we believe that the change in the COP pathway and plantar pressure in normal feet when stepping over an obstacle is due to the normal center of mass translation that helps the person balance as the obstacle heights are increased. However, the center of mass translation in flat feet may differ from that of normal feet when crossing obstacles at different heights due to a low longitudinal arch.
Acknowledgement This research was supported by the Kyungsung University Research Grant in 2014.
References [1]
[2]
Ledoux WR, Hillstrom H. The distributed plantar vertical force of neutrally aligned and pes planus feet. Gait Posture. 2002; 15(1): 1–9. Shibuya N, Jupiter DC, Ciliberti LJ, VanBuren V, Fontaine JL. Characteristics of adult flatfoot in the United States. J Foot Ankle Sur. 2010; 49(4): 363–368.
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Root ML, Orien WP, Weed JH. Normal and abnormal function of the foot. Los Angeles: Clinical Biomechanics Corporation Publisher; 1997. [4] Simkin A, Leichter I, Giladi M. Combined effect of foot arch structure and orthotic device on stress fractures. Foot Ankle. 1989; 10(1): 25–29. [5] Bertani A, Cappello A, Benedetti MG, Simoncini L, Catani F. Flat foot functional evaluation using pattern recognition of ground reaction data. Clin Biomech. 1999; 14(7): 484–493. [6] Qeen R, Mall N, Nunley J, Chuckpaiwong B. Differences in plantar loading between flat and normal feet during different athletic tasks. Gait Posture. 2009; 29(4): 582–586. [7] Winter DA. Human balance and posture control during standing and walking. Gait Posture. 1995; 3(4): 193–214. [8] Wang Y, Watanabe K. The relationship between obstacle height and center of pressure velocity during obstacle crossing. Gait Posture. 2008; 27(1): 172–175. [9] Kenneth JC, Lisa SS, Marcus PB. Comparison of an in-shoe pressure measure device to a force plate: concurrent validity of center of pressure measurements. Gait Posture. 2000; 12(2): 128–133. [10] Han TR, Paik NJ, Im MS. Quantification of the path of center of pressure (COP) using an F-scan in-shoe transducer. Gait Posture. 1999; 10(3): 248–254. [11] Ledoux WR, Hillstrom HJ. The distributed plantar vertical force of neutrally aligned and pes planus feet. Gait Posture. 2002; 15(1): 1–9.
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Chuckpaiwong B, Nunley J, Mall N, Qeen R. The effect of foot type on in-shoe plantar pressure during walking and running. Gait Posture. 2008; 28(3): 401–411. Mall NA, Hardaker WM, Nunley JA, Queen RM. The reliability and reproducibility of foot type measurements using a mirrored foot photo box and digital photography compared to caliper measurements. J Biomech. 2007; 40(5): 1171–1176. Shiang TY, Lee SH, Lee SJ. Evaluating different footprint parameters as a predictor of arch height. IEEE Eng Med Biol. 1998; 17(6): 62–66. Kanatli Uu, Gözil RR, Besli KK, Yetkin HH, Bölükbasi SS. The relationship between the hindfoot angle and the medial longitudinal arch of the foot. Foot Ankle Int. 2006; 27(8): 623–627. Giacomozzi C. Appropriateness of plantar pressure measurement devices: a comparative technical assessment. Gait Posture. 2010; 32(1): 141–144. Menz HB, Morris ME. Clinical determinants of plantar force and pressure during walking in older people. Gait Posture. 2006; 24(2): 229–236. Kernozek TW, LaMott EE. Comparisons of plantar pressure between the elderly and young adults. Gait Posture. 1995; 3(3): 143–148. Han JT, Koo HM, Jung JM, Kim YJ, LEE JH. Differences in plantar foot pressure and COP between flat and normal feet during walking. J Phys Ther Sci. 2011; 23(4): 683–685.
Journal of Back and Musculoskeletal Rehabilitation 28 (2015) 629–633 DOI 10.3233/BMR-130449 IOS Press
Comparison of plantar pressure between flat and normal feet when crossing an obstacle at different heights Jin-Tae Hana , Jung-Hoon Leeb,∗, Eun-Ju Leec, Chang-Hun Limd and Won-Bok Kime a
Department of Physical Therapy, College of Science, Kyungsung University, Busan, Korea Department of Physical Therapy, College of Nursing and Healthcare Sciences, Dong-Eui University, Busan, Korea c Department of Physical Therapy, Busan ST. Marrys Medical Center, Busan, Korea d Department of Physical Therapy, Gangneung Yeongdong College, Gangneung, Korea e Department of Physical Therapy, Daegu University, Daegu, Korea b
Abstract. OBJECTIVE: The purpose of this study is to compare the plantar foot pressure and the center of pressure (COP) pathway of normal and flat feet while crossing an obstacle at different heights. METHODS: Nineteen subjects (10 normal feet, 9 flat feet) participated in this study. The plantar foot surface was divided into the following seven regions for pressure measurement: two toe regions, three forefoot regions, one midfoot region, and one heel region. A one-way ANOVA with repeated measurements was used to compare the plantar foot pressure of normal and flat feet according to the obstacle height. RESULTS: The trend analysis showed a quadratic trend during level walking for the normal foot group, but a linear trend appeared as the obstacle height increased. In the flat foot group, the trend analysis showed a linear trend regardless of the obstacle height. In the 2nd-3rd metatarsal head region, the plantar pressure of the flat foot group increased more than the normal foot group as the obstacle height increased; however, in the 4th-5th metatarsal head region, the plantar pressure in flat feet was lower than in normal feet. In the heel region, the plantar pressure in both groups generally increased as the obstacle height increased, but the plantar pressure in the flat foot group was lower than in the normal foot group. CONCLUSION: We believe that, due to a loss of longitudinal arch, the COP path and plantar pressure of flat feet may be different from normal feet when crossing obstacles of different heights. Keywords: Plantar pressure, obstacle, flat foot, pathway of COP
1. Introduction The foot provides the interaction between the body and the ground. It also serves as a controllable mechanism and rigid lever [1]. However, flat feet make these ∗ Corresponding author: Jung-Hoon Lee, Department of Physical Therapy, College of Nursing and Healthcare Sciences, Dong-Eui University, 176, Eomgwangno, Busanjin-gu, Busan, 614-714, Korea. Tel.: +82 51 890 4222; Fax: +82 51 890 4229; E-mail: dreampt@ hanmail.net.
functions difficult. A flat foot is defined as a foot with an absent or abnormally low longitudinal arch height and pronation [2,3]. People with a low arch may be at an increased risk of metatarsal stress fractures [4]. Flat feet may also be responsible for the following: ligament laxity, muscle fatigue, foot/ankle instability, and valgus hindfoot due to inappropriate plantar loading [5,6]. Stepping over an obstacle is particularly associated with a shift in the center of mass closer to the supporting edge and large inertial forces, which threatens balance [7].
c 2015 – IOS Press and the authors. All rights reserved ISSN 1053-8127/15/$35.00
630
J.-T. Han et al. / Comparison of plantar pressure between flat and normal feet
Stepping over an obstacle is very demanding and poses great risk when the foot’s motor function is poor [8]. When crossing obstacles, the plantar pressure is consistently modified and varies more at different obstacle heights. Plantar pressure can provide information about the foot loading changes with obstacles [9,10]. In some previous studies, the plantar pressure of normal and flat feet was compared [6,11,12], but most studies examined the differences only when walking on an even surface. In addition, few studies have quantitatively characterized the plantar foot pressure and the pathway of COP while crossing obstacles at different heights. Therefore, the aim of this study was to investigate the differences between flat and normal feet in plantar pressure and the COP pathway when crossing obstacles at different heights. It was hypothesized that the plantar pressure and pathway of COP would be modified in people with flat feet when crossing obstacles and that these factors may change more when crossing at different heights.
2. Materials and methods 2.1. Subjects Nineteen subjects (10 normal feet, 8 flat feet) participated in this study and were divided into two groups, one with flat and one with normal feet. Subjects were excluded for having musculoskeletal or neurological problems that would hinder a normal stance (e.g., osteoarthritis, ankle/foot deformities, nerve deficits, or brain injury). Prior to the start of the study the subjects signed an informed-consent document. 2.2. Navicular height and rear foot angle Each subject’s feet were marked at the following bony landmarks: the navicular tuberosity, the midline of the posterior calcaneal tuberosity, and the midline of the Achilles tendon [13]. We measured the navicular height and the rear foot angle of subjects with a measuring tape line and goniometer, respectively. The navicular height was defined as the height between the floor and the navicular tuberosity [14]. The rear foot angle was defined as the angle between the midcalcaneal line and the mid-Achilles line [6]. Subjects with a navicular height of less than 37 mm and a rear foot angle of more than 6◦ were considered to have flat feet [15].
Table 1 Common characteristics of subjects (Mean ± SD) Variables Normal feet (n = 10) Flat feet (n = 8) Age 20.60 ± 0.70 21.13 ± 1.64 Height (cm) 164.60 ± 9.71 165.38 ± 6.80 Weight (kg) 55.53 ± 9.11 58.75 ± 8.65 Foot sides (cm) 247.50 ± 14.58 246.88 ± 14.13 Navicular height (cm) 4.17 ± 0.31 2.80 ± 0.21∗ Rear foot angle (◦ ) 2.48 ± 0.79 6.27 ± 0.35∗ SD: Standard deviation. ∗ Significant difference (p < 0.05) between normal and flat feet.
2.3. Plantar foot pressure Plantar foot pressure data were recorded using the Matscan system (Tekscan, USA). The pressure sensor width was 702.579 mm, and the sensors were composed of a 44 × 52 matrix. The pressure distribution data were collected at 60 frames per second using the Tekscan Pressure Measurement System, Version 5.23 to analyze plantar foot pressure. Although a complex ad hoc calibration was necessary, Tekscan had a high accuracy [16]. For the pressure measurement, the foot was divided into the following seven plantar regions: two toe regions, three forefoot regions, one midfoot region, and one heel region [17]. The toe region was subdivided into two regions (i.e., the hallux and the lesser toes). The three forefoot regions underneath the metatarsal heads were subdivided into equal thirds. The medial forefoot region was underneath the first metatarsal head, the central region was underneath the second and third metatarsal heads, and the lateral region was underneath the fourth and fifth metatarsal heads. 2.4. Procedure All subjects were asked to pass the right foot above the Matscan while crossing the obstacles at different heights with bare feet. All trials were performed twice, and the average of both trials was used to analyze the data. The plantar pressures were measured, and the COP trends were found. 2.5. Statistical analysis In this study, the pressure and the pathway of COP were measured in subjects with normal and flat feet when crossing obstacles at different heights. A simple regression was used to estimate the pathway of COP between normal and flat feet during obstacle crossing with different heights. The curve trend was analyzed using the COP pathway from the heel to forefoot. We
J.-T. Han et al. / Comparison of plantar pressure between flat and normal feet
631
Table 2 Comparison between normal and flat feet in the plantar foot pressure at seven plantar foot areas when crossing obstacles at different heights (Mean ± SD) Plantar foot area Hallux Lesser toe 1st MPJ 2–3 MPJ 4–5 MPJ Midfoot Heel
No obstacle Normal Flat 212.26 ± 101.75 251.75 ± 70.11 64.62 ± 26.79 70.05 ± 28.17 165.28 ± 77.48 165.39 ± 35.31 268.80 ± 40.29 310.28 ± 84.92 127.33 ± 45.64 78.39 ± 29.99 50.82 ± 32.93 61.68 ± 41.93 248.37 ± 37.85 198.21 ± 32.91
10 cm obstacle Normal Flat 229.03 ± 98.97 306.94 ± 81.96 66.43 ± 25.12 98.48 ± 47.41 164.35 ± 103.25 144.74 ± 41.67 268.45 ± 59.51 298.66 ± 74.69 116.03 ± 40.60 67.32 ± 12.33∗ 48.87 ± 35.13 62.28 ± 30.51 282.44 ± 52.20† 214.59 ± 44.62∗
20 cm obstacle Normal Flat 226.85 ± 89.28 299.81 ± 79.23 59.90 ± 17.88 97.33 ± 37.78∗‡ 163.32 ± 55.78 154.74 ± 29.22 287.58 ± 80.99 346.19 ± 88.52‡# 134.18 ± 63.06 78.69 ± 22.35∗ # 72.80 ± 42.12 60.22 ± 38.92 278.85 ± 49.60‡ 219.05 ± 48.85∗
Unit: kPa, SD: Standard deviations. ∗ Significant difference (p < 0.05) between normal and flat feet, † Significant difference (p < 0.05) between no obstacle and 10 cm obstacle, ‡ Significant difference (p < 0.05) between no obstacle and 20 cm obstacle, # Significant difference (p < 0.05) between 10 cm obstacle and 20 cm obstacle.
Fig. 1. Comparison of the COP pathway between normal and flat feet when crossing obstacles at different heights.
used a one-way ANOVA with repeated measurements to compare the differences in the plantar pressure by obstacle height in the normal and flat feet groups. An alpha level of 0.05 was used to test for significance. All data were analyzed using the SPSS 18.0 statistical software.
3. Results Table 1 shows the characteristics of the subjects who were divided into the normal and flat feet groups. Figure 1 represents the COP pathway of the normal and flat feet groups when crossing obstacles at different heights. The trend analysis showed a quadratic trend of COP during level walking for the normal feet group (R2 = 0.032), but a linear trend appeared as the obstacle heights increased (10 cm: R2 = 0.225, 20 cm: R2 = 0.587). However, for the flat feet group, the trend analysis showed a linear trend regardless of the obstacle
height (0 cm: R2 = 0.994, 10 cm: R2 = 0.930, 20 cm: R2 = 0.946). There is a linear trend as R2 moves closer to 1. Table 2 compares the plantar pressure in each foot region when stepping over obstacles at different heights. In the hallux and the lesser toe region, the planar pressure in the flat feet group was higher than that of the normal feet group during level walking and obstacle crossing and increased as obstacle height increased. In the lesser toe region, there was a significant difference between the normal and flat feet group at 20 cm obstacle and there was statistically significant difference by obstacle height at flat feet group. However, the plantar pressure of the flat foot group in the 1st metatarsal head region was lower than the normal foot group and decreased as the obstacle height increased and there was also no difference between the normal and flat feet group. In the 2nd –3rd metatarsal head region, the plantar pressure in the flat foot group significantly increased as obstacle
632
J.-T. Han et al. / Comparison of plantar pressure between flat and normal feet
height increased (p < 0.05), but there was no statistically significant difference between the normal and flat foot groups (Table 2). In the 4th –5th metatarsal head region, plantar pressure in the normal foot group increased, but that of the flat feet group decreased. There was no difference in plantar pressure with obstacle height, but plantar pressure of the flat foot group was significantly lower than the normal foot group (p < 0.05). In the midfoot region, there was no difference in plantar pressure between the normal and flat foot group; however, the plantar pressure of the normal foot group when crossing obstacles was higher than that of the flat foot group and there was significantly increased at 20 cm height obstacle (p < 0.05) (Table 2). In the heel region, the plantar pressure increased as the obstacle height increased, and the plantar pressure of the flat foot group was significantly lower than that of the normal foot group (p < 0.05) (Table 2).
4. Discussion The results of this study showed that the pathway of COP in the normal feet group showed a quadratic trend while walking on an even surface and showed a linear trend as the obstacle height increased but that of the flat foot group showed a linear trend regardless of obstacle height. Additionally, the plantar pressure of the 2nd – 3rd metatarsal head and heel regions increased in both the normal and flat foot groups as the obstacle height increased. The plantar pressure of the 4–5th metatarsal head regions of the normal foot groups increased as the obstacle height increased but that of the flat feet group decreased. There was a significant difference between the normal and flat foot groups when obstacles crossing. The COP pathway in normal subjects begins at the heel and ends at the hallux and slightly shifts medially in the forefoot when walking on even surfaces [17,18]. The results of our study agree with previous studies of walking on level ground, and the difference between normal and flat foot groups are understood [6]. However, as the obstacle height increases, the COP path was shorter and straighter in flat feet as compared to normal feet. The results of our study agree with the previous literature that reported that the plantar pressure of flat feet was commonly higher than that of normal feet. In our study, the plantar pressure of the hallux and 2nd –3rd metatarsal head was higher in flat feet than normal feet and increased as the obstacle height increased. A few studies reported that plantar loading
beneath the midfoot was higher in flat feet than normal feet6 and that this increase in foot loading is due to a different foot type during walking [6,11,12]. However, the plantar pressure of the midfoot and heel regions as obstacle height increased was lower in flat feet than normal feet in our study. This finding indicates that the center of mass was more concentrated in the forefoot than the rearfoot for the propulsive force to step over the obstacle; therefore, we agree that the center of mass in flat feet shifts medially because of a loss in the foot arch [19]. This study was conducted to determine the plantar pressure and the COP pathway in subjects with normal and flat feet when crossing obstacles at different heights. The COP pathway of the normal feet group showed a quadratic trend when walking on an even surface and a linear trend as the obstacle height increased. However, the COP pathway in the flat feet group showed a linear pathway without regard to the obstacle height. In the 2nd –3rd metatarsal heads and the heel region, the plantar pressure increased as the obstacle height increased in both the normal and flat foot groups. The pressure of the 4th –5th metatarsal head regions of the normal foot group increased but that of the flat feet group decreased. This shows that the center of mass normally transfers forward and laterally as the obstacle height increases, but the flat foot group was already shifted medially due to a loss of the longitudinal arch. In conclusion, we believe that the change in the COP pathway and plantar pressure in normal feet when stepping over an obstacle is due to the normal center of mass translation that helps the person balance as the obstacle heights are increased. However, the center of mass translation in flat feet may differ from that of normal feet when crossing obstacles at different heights due to a low longitudinal arch.
Acknowledgement This research was supported by the Kyungsung University Research Grant in 2014.
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