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Phys. Ther. Korea 2022; 29(3): 208-214

Published online August 20, 2022

https://doi.org/10.12674/ptk.2022.29.3.208

© Korean Research Society of Physical Therapy

The Immediate Effect of Medial Arch Support on Dynamic Knee Valgus During Stair Descent and Its Relationship With the Severity of Pronated Feet

Hwa-ik Yoo1,2 , BPT, PT, Sung-hoon Jung2,3 , PhD, PT, Do-eun Lee1,2 , BPT, PT, Il-kyu Ahn1,2 , BPT, PT, Oh-yun Kwon2,3 , PhD, PT

1Department of Physical Therapy, The Graduate School, Yonsei University, 2Kinetic Ergocise Based on Movement Analysis Laboratory, 3Department of Physical Therapy, College of Software and Digital Healthcare Convergence, Yonsei University, Wonju, Korea

Correspondence to: Oh-yun Kwon
E-mail: kwonoy@yonsei.ac.kr
https://orcid.org/0000-0002-9699-768X

Received: June 7, 2022; Revised: July 7, 2022; Accepted: July 8, 2022

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Background: Pronated foot posture (PFP) contributes to excessive dynamic knee valgus (DKV). Although foot orthoses such as medial arch support (MAS) are widely and easily used in clinical practice and sports, few studies have investigated the effect of MAS on the improvement of DKV during stair descent in individuals with a PFP. Moreover, no studies reported the degree of improvement in DKV according to the severity of PFP when MAS was applied. Objects: This study aimed to examine the immediate effect of MAS on DKV during stair descent and determine the correlation between navicular drop distance and changes in DKV when MAS is applied.
Methods: Twenty individuals with a PFP (15 males and five females) participated in this study. The navicular drop test was used to measure PFP severity. The frontal plane projection angle (FPPA) was calculated under two conditions, with and without MAS application, using 2-dimensional video analysis.
Results: During stair descent, the FPPA with MAS (173.1° ± 4.7°) was significantly greater than that without MAS (164.8° ± 5.8°) (p < 0.05). There was also a significant correlation between the navicular drop distance and improvement in the FPPA when MAS was applied (r = 0.453, p = 0.045).
Conclusion: MAS application can affect the decrease in DKV during stair descent. In addition, MAS application should be considered to improve the knee alignment for individuals with greater navicular drop distance.

Keywords: Flatfoot, Foot orthoses, Genu valgum

Dynamic knee valgus (DKV) can produce harmful joint moments in the lower extremities during weight-bearing movements, including hip adduction and internal rotation, tibial external rotation, and ankle eversion [1]. Therefore, DKV that occurs during various weight-bearing movements has been frequently associated with the development of lower extremity injuries such as anterior cruciate ligament rupture and patellofemoral pain syndrome [2,3]. In previous studies, deficits in knee extensor strength [4,5], hip abductor and external rotator strength [6,7], and range of motion of ankle dorsiflexion [8,9] have been considered as contributing factors for increasing DKV during single-leg movements in weight-bearing conditions. Although several functions of the hip, knee, and ankle joints have been studied to clarify their association with DKV, few studies have examined the relationship between foot posture and DKV [10].

Considering the kinematic system of the lower extremities, foot posture is also a crucial factor in the occurrence of DKV. Recent literature suggests that a pronated foot posture (PFP) accompanying medial tilting of the tibia can produce greater DKV during single-leg movements, such as stair descent, squatting, and landing [11,12]. In a previous study [12], the frontal plane projection angle (FPPA) and knee-in distance indicated that the degree of DKV was significantly greater in individuals with a PFP than in those without a PFP during stair descent. During stair descent, medial tilting of the tibia due to a PFP can lead to increased medial displacement of the knee joint, and eventually, the combination of lateral pelvic displacement and medial knee displacement can produce excessive DKV. Therefore, PFP should be considered a contributing factor to excessive DKV, trunk stability, and hip and knee joint functions.

Foot orthoses are widely used to increase the medial arch support (MAS) by limiting PFP. Although previous studies have investigated the effects of foot orthoses on changes in hip and knee joint kinematics during walking or running [13-16], changes in lower extremity kinematics during stair descent have not been well established. As stair descent requires a sufficient range of motion, muscle strength in the lower extremities, and dynamic stability of distal joints, such as the foot and ankle joints, for controlling closed kinetic movement [17-19], it is often challenging for individuals to control their lower extremity alignment during stair descent. Furthermore, PFP can affect DKV during stair descent [12]. Thus, MAS should also be considered as an intervention to reduce DKV during stair descent, as well as muscle strengthening and balance training, with lower limb positioning feedback [10]. However, no studies have reported the effect of MAS on DKV during stair descent. Investigating the improvement in DKV when wearing MAS during stair descent in individuals with a PFP could provide helpful information for managing faulty movement patterns of the lower extremity.

Previous researchers have focused on the relationship between DKV and muscle strength of the hip abductor, hip external rotator, knee extensor, and range of motion of ankle dorsiflexion with and without weight-bearing [9,20-22]. However, according to the severity of PFP, no studies have reported the relationship between the improvement in DKV when MAS is applied and foot postures associated with PFP, such as navicular drop distance. Therefore, this study aimed to examine the immediate effect of MAS on DKV during stair descent in individuals with a PFP and determine the degree of association between the navicular drop distance and improved DKV when MAS is applied. We hypothesized that the use of MAS would reduce DKV during stair descent.

1. Participants

This cross-sectional study was conducted in a laboratory setting between December 2021 and January 2022. Based on the pilot data (differences in FPPA measurements between the two conditions, with and without MAS) gathered from seven individuals with a PFP, the sample size was calculated using G-power software (version 3.1.9.4; University of Trier, Trier, Germany). A priori analysis set a power of 0.8, α = 0.05, and an effect size of 0.695. A sample size of at least 19 participants was required. The PFP of each participant was assessed using the foot posture index (FPI), which is a simple method for evaluating foot posture [23]. The FPI consists of six observations of the rearefoot and forefoot posture in a standing position. The rearfoot posture was assessed by palpation of the head of the talus, observation of the curves above and below the lateral malleoli and the extent of the inversion/eversion of the calcaneus. The forefoot posture was assessed by observation of the burge in the region of the talonavicular joint, the congruence of the medial longitudinal arch and the extent of abduction/adduction of the forefoot on the rearfoot [23,24]. If the FPI score (range from –12 to +12) was ≥ 6, it was classified as a PFP. Individuals were excluded if they had a history of injury or surgery of the lower extremity: musculoskeletal disorders in the ankle or foot, such as plantar fasciitis or tendinopathy; or systemic diseases, such as diabetes or connective tissue disorders [12,25]. Twenty individuals with a PFP (15 males and five females; FPI score, 10.4 ± 3.3; age, 26.2 ± 1.9 y; height, 171.2 ± 8.5 cm; body mass 71.3 ± 11.2 ㎏; dominant side, 20 right) were recruited. Before the study, the details of the experimental procedures were explained to all participants, and informed consent was obtained from them on enrollment, which was approved by the Institutional Review Board of Yonsei University Mirae Campus (IRB no. 1041849-202110-BM-162-01).

2. Medial Arch Support

Participants with a PFP performed stair descent under two conditions (with and without MAS). In this study, three sizes of MAS (Arch support cushions; FootMatters Co., Ltd., Grand Haven, MI, USA) were used and selected according to each participant’s foot size. This MAS was made of rigid rubber. The MAS was inserted under the medial longitudinal arch of the foot under barefoot conditions (Figure 1).

Figure 1. Medial arch support application.

3. Navicular Drop Test

The navicular drop test, first introduced by Brody [26], is widely used to assess the amount of foot pronation. The test method was standardized, as previously described by Headlee et al. [27]. The navicular drop was determined as the distance change in the navicular tuberosity in the sagittal plane between the ankle joint in the subtalar neutral position during sitting and relaxed standing. The neutral sitting position was standardized as the participant sat on a chair with 90° knee flexion, with their feet in the subtalar neutral position contacting the floor, and without any weight application. The first distance between the floor and midpoint of the navicular tuberosity measured in the sitting position was recorded on an index card. Similarly, the second distance was recorded in a relaxed standing position (Figure 2). Changes in these two distances were calculated using a digital caliper (BD500-300; Bluetec, Seoul, Korea).

Figure 2. Measurement of the navicular drop distance. (A) Sitting position, (B) standing position.

4. Two-dimensional Video Analysis

Following previous protocols [12], a smartphone (Galaxy S10e; Samsung Inc., Seoul, Korea) with a video recording application was placed on a tripod. The tripod's height was adjusted so that the center of the camera lens was set at the height of the patella of the participants while standing on a 15-cm step box. In addition, the tripod was placed 250 cm in front of the step box. All recorded videos were analyzed using the available software package of Kinovea® (version 0.8.15; Kinovea, Bordeaux, France). The FPPA, determined by the angle between the line connecting the anterior superior iliac spine and the center of the patella and the line connecting the center of the patella and the middle of the ankle joint, was used to calculate DKV during stair descent (Figure 3). The alignment was considered neutral at 180°; an FPPA of < 180° indicated knee valgus alignment, and > 180° indicated knee varus alignment [28].

Figure 3. Measurement of the frontal plane projection angle during stair descent.

5. Procedures

The participants were asked to complete a simple questionnaire that included their age, sex, height, and body mass. The participants were also evaluated to ensure that they met the inclusion criteria. The participants wore fitted shorts, and the dominant leg of each participant was tested barefoot. The dominant leg was defined as the participant’s preferred kicking limb [20]. PFP was assessed using the FPI score and the navicular drop test. Four retroreflective circular markers (14 mm in diameter) were placed at both the anterior superior iliac spines, the midpoint of the patella, and middle of both malleoli. The participants then descended the stairs from a 15-cm step box [9,20]. During the stair descent, the dominant leg supported the body weight, and the heel of the non-dominant leg gently touched the floor. The participants were instructed to clasp their hands behind their backs to capture the markers and prevent compensatory movements of the upper extremities or trunk. Next, the MAS was placed under the medial longitudinal arch of the dominant lower limb, and the same protocol was repeated. The mean values of the two trials were used for the data analysis.

6. Statistical Analysis

All statistical analyses were performed using SPSS version 25.0 (IBM Co., Armonk, NY, USA). The level of statistical significance was set at p < 0.05. The Shapiro–Wilk test was used to assess data normality. Descriptive statistics are expressed as the mean and standard deviation (SD). Paired t-tests were used to compare the FPPA during stair descent between the two conditions (with and without MAS). Pearson product-moment (r) correlation coefficients were used to determine the relationship between the navicular drop distance and the improvement ratio of FPPA when MAS was applied ([FPPA with MAS/FPPA without MAS] × 100). The r value was constained to lie between 0 (no effect) and 1 (maximal effect); 0 ≤ r < 0.1 was classified as no effect, 0.1 ≤ r < 0.3 was a small effect, 0.3 ≤ r < 0.5 was a moderate effect, and r ≤ 0.5 was a large effect [29].

The Shapiro–Wilk test showed the normality of the data (p > 0.05). During stair descent, the FPPA with MAS was significantly greater than that without MAS (with MAS: 173.1° ± 4.7°; without MAS: 164.8° ± 5.8°; p < 0.05) (Figure 4). Table 1 shows the correlation coefficients between the navicular drop distance (9.4 ± 3.2 mm) and improvement in the FPPA (105.2% ± 2.8%) when MAS was applied. There was a significant correlation between the navicular drop distance and improvement in the FPPA (r = 0.453, p = 0.045).

Table 1 . Correlation coefficient between the navicular drop distance and changes in the FPPA when MAS was applied.

VariableChange in FPPA

rp
Navicular drop distance (mm)0.4530.045*


Figure 4. The difference in the FPPAs with and without MAS application. FPPA, frontal plane projection angle; MAS, medial arch support. *p < 0.05.

As a compressive force equivalent to approximately 6 times the body mass can be generated at the knee joint during stair descent [30], the malalignment of the knee joint that results in inadequate load transfer should be corrected. This study compared the FPPA during stair descent between two conditions (with and without MAS). Consistent with our hypotheses, the FPPA when MAS was applied (173.1°) was greater than that without MAS (164.8°). Accordingly, MAS application can reduce DKV that occurs in the knee joint during stair descent. In addition, the increase in the FPPA according to MAS application was observed as the navicular drop distance increased. Thus, in managing DKV that occurs during stair descent, MAS application should be considered for individuals with a large navicular drop distance.

Considering the characteristics of closed chain activities, lower extremity motions are interdependent, and excessive movement in one joint may lead to the accumulation of stress in the other joint. From this perspective, excessive foot pronation causes excessive tibial internal rotation, hip adduction, and hip internal rotation, which can increase the DKV, resulting in patellofemoral pain [31]. Bonifácio et al. [32] reported a reduction in hip adduction (mean difference, –1.8°) and hip internal rotation (mean difference, –2.1°) when MAS was applied during stair descent compared with the flat insole. Furthermore, they reported that better ankle control was possible with a decrease in tibialis anterior and abductor hallucis muscle activity when MAS was applied. Thus, distally, MAS can positively affect the correction of PFP and controls excessive motions that are transferred proximally. This may be a possible reason for the decrease in DKV when MAS was used in our study.

In a previous study by Bonifácio et al. [32], only healthy participants with a mean FPI score of +5 (SD = 4) were recruited, indicating that the sample did not express excessive foot pronation. However, the participants in our study had a relatively severe PFP with a mean FPI score of +7.5 (SD = 1.6) and a mean navicular drop distance of 9.4 mm (SD = 3.2). As no studies have examined the degree of improvement in knee malalignment when MAS is applied according to the severity of PFP, we found a correlation between the navicular drop distance and changes in the FPPA when MAS was applied. There was a significant correlation between the navicular drop distance and changes in the FPPA when MAS was used (r = 0.453, p = 0.045). These data indicate that individuals with a large navicular drop distance can show an increased improvement in DKV during stair descent when MAS is applied.

Knee alignment with more DKV can lead to external knee abduction moment relative to lower extremity problems, such as anterior cruciate ligament rupture and knee osteoarthritis [33]. In addition, the external knee abduction moment increases with strain load at the anterior cruciate ligament and medial collateral ligament and lateral bowstring force on the patella [34]. Although kinetic data such as knee abduction moment were not measured in this study, our findings that DKV decreased when MAS was applied would demonstrate a reduction in external knee abduction moment. Further studies using a 3-dimensional motion capture system and a force plate are needed to examine the positive effect of MAS on kinetic variables.

The major difference between the FPI score and navicular drop test to evaluate PFP was the presence or absence of change in weight-bearing during the assessments. The navicular drop test was first suggested by Brody [26], who presented the difference between navicular height in the neutral and relaxed subtalar joint positions. In this study, an alternative for the navicular drop test (sit-to-stand) was described by McPoil et al. [35] and Headlee et al. [27], which improved the poor inter-rater reliability by placing the subtalar joint in a neutral position using palpation. The changes in weight bearing that occurred during the dynamic navicular drop test would reflect the function of the medial longitudinal arch as the primary load-bearing and shock-absorbing structure of the foot during stair descent [36]. Thus, the navicular drop test can be a helpful method at a moderate level (r = 0.453) to predict a significant decrease in DKV during stair descent when MAS is applied.

This study has several limitations. First, the sample size was small. Further studies are required to generalize these results. Second, the sex ratios were not equal. Third, participants with an excessive PFP (FPI score > 10 or navicular drop distance > 10–15 mm) were excluded. Fourth, 2-dimensional video analysis revealed perspective errors in the sagittal and transverse planes. Finally, we measured only lower limb kinematics. Further research is needed to investigate the effects of MAS on kinetic information (electromyography and ground reaction force) during stair descent according to the severity of PFP while resolving sex differences.

PFP could be a contributing factor to the development of DKV during stair descent. In this study, DKV was significantly reduced when MAS was applied during stair descent. Moreover, participants who had a greater navicular drop distance showed greater improvement in DKV when MAS was applied. These findings indicate that clinicians can apply MAS to manage knee joint malalignment during stair descent, especially for individuals with a large navicular drop distance.

No potential conflict of interest relevant to this article was reported.

Conceptualization: HY, OK. Data curation: DL, IA. Formal analysis: DL, IA. Investigation: HY, IA. Methodology: HY, SJ, OK. Project administration: IA. Supervision: SJ, OK. Validation: OK. Visualization: DL. Writing - original draft: HY. Writing- review & editing: HY, SJ, OK.

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Article

Original Article

Phys. Ther. Korea 2022; 29(3): 208-214

Published online August 20, 2022 https://doi.org/10.12674/ptk.2022.29.3.208

Copyright © Korean Research Society of Physical Therapy.

The Immediate Effect of Medial Arch Support on Dynamic Knee Valgus During Stair Descent and Its Relationship With the Severity of Pronated Feet

Hwa-ik Yoo1,2 , BPT, PT, Sung-hoon Jung2,3 , PhD, PT, Do-eun Lee1,2 , BPT, PT, Il-kyu Ahn1,2 , BPT, PT, Oh-yun Kwon2,3 , PhD, PT

1Department of Physical Therapy, The Graduate School, Yonsei University, 2Kinetic Ergocise Based on Movement Analysis Laboratory, 3Department of Physical Therapy, College of Software and Digital Healthcare Convergence, Yonsei University, Wonju, Korea

Correspondence to:Oh-yun Kwon
E-mail: kwonoy@yonsei.ac.kr
https://orcid.org/0000-0002-9699-768X

Received: June 7, 2022; Revised: July 7, 2022; Accepted: July 8, 2022

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background: Pronated foot posture (PFP) contributes to excessive dynamic knee valgus (DKV). Although foot orthoses such as medial arch support (MAS) are widely and easily used in clinical practice and sports, few studies have investigated the effect of MAS on the improvement of DKV during stair descent in individuals with a PFP. Moreover, no studies reported the degree of improvement in DKV according to the severity of PFP when MAS was applied. Objects: This study aimed to examine the immediate effect of MAS on DKV during stair descent and determine the correlation between navicular drop distance and changes in DKV when MAS is applied.
Methods: Twenty individuals with a PFP (15 males and five females) participated in this study. The navicular drop test was used to measure PFP severity. The frontal plane projection angle (FPPA) was calculated under two conditions, with and without MAS application, using 2-dimensional video analysis.
Results: During stair descent, the FPPA with MAS (173.1° ± 4.7°) was significantly greater than that without MAS (164.8° ± 5.8°) (p < 0.05). There was also a significant correlation between the navicular drop distance and improvement in the FPPA when MAS was applied (r = 0.453, p = 0.045).
Conclusion: MAS application can affect the decrease in DKV during stair descent. In addition, MAS application should be considered to improve the knee alignment for individuals with greater navicular drop distance.

Keywords: Flatfoot, Foot orthoses, Genu valgum

INTRODUCTION

Dynamic knee valgus (DKV) can produce harmful joint moments in the lower extremities during weight-bearing movements, including hip adduction and internal rotation, tibial external rotation, and ankle eversion [1]. Therefore, DKV that occurs during various weight-bearing movements has been frequently associated with the development of lower extremity injuries such as anterior cruciate ligament rupture and patellofemoral pain syndrome [2,3]. In previous studies, deficits in knee extensor strength [4,5], hip abductor and external rotator strength [6,7], and range of motion of ankle dorsiflexion [8,9] have been considered as contributing factors for increasing DKV during single-leg movements in weight-bearing conditions. Although several functions of the hip, knee, and ankle joints have been studied to clarify their association with DKV, few studies have examined the relationship between foot posture and DKV [10].

Considering the kinematic system of the lower extremities, foot posture is also a crucial factor in the occurrence of DKV. Recent literature suggests that a pronated foot posture (PFP) accompanying medial tilting of the tibia can produce greater DKV during single-leg movements, such as stair descent, squatting, and landing [11,12]. In a previous study [12], the frontal plane projection angle (FPPA) and knee-in distance indicated that the degree of DKV was significantly greater in individuals with a PFP than in those without a PFP during stair descent. During stair descent, medial tilting of the tibia due to a PFP can lead to increased medial displacement of the knee joint, and eventually, the combination of lateral pelvic displacement and medial knee displacement can produce excessive DKV. Therefore, PFP should be considered a contributing factor to excessive DKV, trunk stability, and hip and knee joint functions.

Foot orthoses are widely used to increase the medial arch support (MAS) by limiting PFP. Although previous studies have investigated the effects of foot orthoses on changes in hip and knee joint kinematics during walking or running [13-16], changes in lower extremity kinematics during stair descent have not been well established. As stair descent requires a sufficient range of motion, muscle strength in the lower extremities, and dynamic stability of distal joints, such as the foot and ankle joints, for controlling closed kinetic movement [17-19], it is often challenging for individuals to control their lower extremity alignment during stair descent. Furthermore, PFP can affect DKV during stair descent [12]. Thus, MAS should also be considered as an intervention to reduce DKV during stair descent, as well as muscle strengthening and balance training, with lower limb positioning feedback [10]. However, no studies have reported the effect of MAS on DKV during stair descent. Investigating the improvement in DKV when wearing MAS during stair descent in individuals with a PFP could provide helpful information for managing faulty movement patterns of the lower extremity.

Previous researchers have focused on the relationship between DKV and muscle strength of the hip abductor, hip external rotator, knee extensor, and range of motion of ankle dorsiflexion with and without weight-bearing [9,20-22]. However, according to the severity of PFP, no studies have reported the relationship between the improvement in DKV when MAS is applied and foot postures associated with PFP, such as navicular drop distance. Therefore, this study aimed to examine the immediate effect of MAS on DKV during stair descent in individuals with a PFP and determine the degree of association between the navicular drop distance and improved DKV when MAS is applied. We hypothesized that the use of MAS would reduce DKV during stair descent.

MATERIALS AND METHODS

1. Participants

This cross-sectional study was conducted in a laboratory setting between December 2021 and January 2022. Based on the pilot data (differences in FPPA measurements between the two conditions, with and without MAS) gathered from seven individuals with a PFP, the sample size was calculated using G-power software (version 3.1.9.4; University of Trier, Trier, Germany). A priori analysis set a power of 0.8, α = 0.05, and an effect size of 0.695. A sample size of at least 19 participants was required. The PFP of each participant was assessed using the foot posture index (FPI), which is a simple method for evaluating foot posture [23]. The FPI consists of six observations of the rearefoot and forefoot posture in a standing position. The rearfoot posture was assessed by palpation of the head of the talus, observation of the curves above and below the lateral malleoli and the extent of the inversion/eversion of the calcaneus. The forefoot posture was assessed by observation of the burge in the region of the talonavicular joint, the congruence of the medial longitudinal arch and the extent of abduction/adduction of the forefoot on the rearfoot [23,24]. If the FPI score (range from –12 to +12) was ≥ 6, it was classified as a PFP. Individuals were excluded if they had a history of injury or surgery of the lower extremity: musculoskeletal disorders in the ankle or foot, such as plantar fasciitis or tendinopathy; or systemic diseases, such as diabetes or connective tissue disorders [12,25]. Twenty individuals with a PFP (15 males and five females; FPI score, 10.4 ± 3.3; age, 26.2 ± 1.9 y; height, 171.2 ± 8.5 cm; body mass 71.3 ± 11.2 ㎏; dominant side, 20 right) were recruited. Before the study, the details of the experimental procedures were explained to all participants, and informed consent was obtained from them on enrollment, which was approved by the Institutional Review Board of Yonsei University Mirae Campus (IRB no. 1041849-202110-BM-162-01).

2. Medial Arch Support

Participants with a PFP performed stair descent under two conditions (with and without MAS). In this study, three sizes of MAS (Arch support cushions; FootMatters Co., Ltd., Grand Haven, MI, USA) were used and selected according to each participant’s foot size. This MAS was made of rigid rubber. The MAS was inserted under the medial longitudinal arch of the foot under barefoot conditions (Figure 1).

Figure 1. Medial arch support application.

3. Navicular Drop Test

The navicular drop test, first introduced by Brody [26], is widely used to assess the amount of foot pronation. The test method was standardized, as previously described by Headlee et al. [27]. The navicular drop was determined as the distance change in the navicular tuberosity in the sagittal plane between the ankle joint in the subtalar neutral position during sitting and relaxed standing. The neutral sitting position was standardized as the participant sat on a chair with 90° knee flexion, with their feet in the subtalar neutral position contacting the floor, and without any weight application. The first distance between the floor and midpoint of the navicular tuberosity measured in the sitting position was recorded on an index card. Similarly, the second distance was recorded in a relaxed standing position (Figure 2). Changes in these two distances were calculated using a digital caliper (BD500-300; Bluetec, Seoul, Korea).

Figure 2. Measurement of the navicular drop distance. (A) Sitting position, (B) standing position.

4. Two-dimensional Video Analysis

Following previous protocols [12], a smartphone (Galaxy S10e; Samsung Inc., Seoul, Korea) with a video recording application was placed on a tripod. The tripod's height was adjusted so that the center of the camera lens was set at the height of the patella of the participants while standing on a 15-cm step box. In addition, the tripod was placed 250 cm in front of the step box. All recorded videos were analyzed using the available software package of Kinovea® (version 0.8.15; Kinovea, Bordeaux, France). The FPPA, determined by the angle between the line connecting the anterior superior iliac spine and the center of the patella and the line connecting the center of the patella and the middle of the ankle joint, was used to calculate DKV during stair descent (Figure 3). The alignment was considered neutral at 180°; an FPPA of < 180° indicated knee valgus alignment, and > 180° indicated knee varus alignment [28].

Figure 3. Measurement of the frontal plane projection angle during stair descent.

5. Procedures

The participants were asked to complete a simple questionnaire that included their age, sex, height, and body mass. The participants were also evaluated to ensure that they met the inclusion criteria. The participants wore fitted shorts, and the dominant leg of each participant was tested barefoot. The dominant leg was defined as the participant’s preferred kicking limb [20]. PFP was assessed using the FPI score and the navicular drop test. Four retroreflective circular markers (14 mm in diameter) were placed at both the anterior superior iliac spines, the midpoint of the patella, and middle of both malleoli. The participants then descended the stairs from a 15-cm step box [9,20]. During the stair descent, the dominant leg supported the body weight, and the heel of the non-dominant leg gently touched the floor. The participants were instructed to clasp their hands behind their backs to capture the markers and prevent compensatory movements of the upper extremities or trunk. Next, the MAS was placed under the medial longitudinal arch of the dominant lower limb, and the same protocol was repeated. The mean values of the two trials were used for the data analysis.

6. Statistical Analysis

All statistical analyses were performed using SPSS version 25.0 (IBM Co., Armonk, NY, USA). The level of statistical significance was set at p < 0.05. The Shapiro–Wilk test was used to assess data normality. Descriptive statistics are expressed as the mean and standard deviation (SD). Paired t-tests were used to compare the FPPA during stair descent between the two conditions (with and without MAS). Pearson product-moment (r) correlation coefficients were used to determine the relationship between the navicular drop distance and the improvement ratio of FPPA when MAS was applied ([FPPA with MAS/FPPA without MAS] × 100). The r value was constained to lie between 0 (no effect) and 1 (maximal effect); 0 ≤ r < 0.1 was classified as no effect, 0.1 ≤ r < 0.3 was a small effect, 0.3 ≤ r < 0.5 was a moderate effect, and r ≤ 0.5 was a large effect [29].

RESULTS

The Shapiro–Wilk test showed the normality of the data (p > 0.05). During stair descent, the FPPA with MAS was significantly greater than that without MAS (with MAS: 173.1° ± 4.7°; without MAS: 164.8° ± 5.8°; p < 0.05) (Figure 4). Table 1 shows the correlation coefficients between the navicular drop distance (9.4 ± 3.2 mm) and improvement in the FPPA (105.2% ± 2.8%) when MAS was applied. There was a significant correlation between the navicular drop distance and improvement in the FPPA (r = 0.453, p = 0.045).

Table 1 . Correlation coefficient between the navicular drop distance and changes in the FPPA when MAS was applied.

VariableChange in FPPA

rp
Navicular drop distance (mm)0.4530.045*


Figure 4. The difference in the FPPAs with and without MAS application. FPPA, frontal plane projection angle; MAS, medial arch support. *p < 0.05.

DISCUSSION

As a compressive force equivalent to approximately 6 times the body mass can be generated at the knee joint during stair descent [30], the malalignment of the knee joint that results in inadequate load transfer should be corrected. This study compared the FPPA during stair descent between two conditions (with and without MAS). Consistent with our hypotheses, the FPPA when MAS was applied (173.1°) was greater than that without MAS (164.8°). Accordingly, MAS application can reduce DKV that occurs in the knee joint during stair descent. In addition, the increase in the FPPA according to MAS application was observed as the navicular drop distance increased. Thus, in managing DKV that occurs during stair descent, MAS application should be considered for individuals with a large navicular drop distance.

Considering the characteristics of closed chain activities, lower extremity motions are interdependent, and excessive movement in one joint may lead to the accumulation of stress in the other joint. From this perspective, excessive foot pronation causes excessive tibial internal rotation, hip adduction, and hip internal rotation, which can increase the DKV, resulting in patellofemoral pain [31]. Bonifácio et al. [32] reported a reduction in hip adduction (mean difference, –1.8°) and hip internal rotation (mean difference, –2.1°) when MAS was applied during stair descent compared with the flat insole. Furthermore, they reported that better ankle control was possible with a decrease in tibialis anterior and abductor hallucis muscle activity when MAS was applied. Thus, distally, MAS can positively affect the correction of PFP and controls excessive motions that are transferred proximally. This may be a possible reason for the decrease in DKV when MAS was used in our study.

In a previous study by Bonifácio et al. [32], only healthy participants with a mean FPI score of +5 (SD = 4) were recruited, indicating that the sample did not express excessive foot pronation. However, the participants in our study had a relatively severe PFP with a mean FPI score of +7.5 (SD = 1.6) and a mean navicular drop distance of 9.4 mm (SD = 3.2). As no studies have examined the degree of improvement in knee malalignment when MAS is applied according to the severity of PFP, we found a correlation between the navicular drop distance and changes in the FPPA when MAS was applied. There was a significant correlation between the navicular drop distance and changes in the FPPA when MAS was used (r = 0.453, p = 0.045). These data indicate that individuals with a large navicular drop distance can show an increased improvement in DKV during stair descent when MAS is applied.

Knee alignment with more DKV can lead to external knee abduction moment relative to lower extremity problems, such as anterior cruciate ligament rupture and knee osteoarthritis [33]. In addition, the external knee abduction moment increases with strain load at the anterior cruciate ligament and medial collateral ligament and lateral bowstring force on the patella [34]. Although kinetic data such as knee abduction moment were not measured in this study, our findings that DKV decreased when MAS was applied would demonstrate a reduction in external knee abduction moment. Further studies using a 3-dimensional motion capture system and a force plate are needed to examine the positive effect of MAS on kinetic variables.

The major difference between the FPI score and navicular drop test to evaluate PFP was the presence or absence of change in weight-bearing during the assessments. The navicular drop test was first suggested by Brody [26], who presented the difference between navicular height in the neutral and relaxed subtalar joint positions. In this study, an alternative for the navicular drop test (sit-to-stand) was described by McPoil et al. [35] and Headlee et al. [27], which improved the poor inter-rater reliability by placing the subtalar joint in a neutral position using palpation. The changes in weight bearing that occurred during the dynamic navicular drop test would reflect the function of the medial longitudinal arch as the primary load-bearing and shock-absorbing structure of the foot during stair descent [36]. Thus, the navicular drop test can be a helpful method at a moderate level (r = 0.453) to predict a significant decrease in DKV during stair descent when MAS is applied.

This study has several limitations. First, the sample size was small. Further studies are required to generalize these results. Second, the sex ratios were not equal. Third, participants with an excessive PFP (FPI score > 10 or navicular drop distance > 10–15 mm) were excluded. Fourth, 2-dimensional video analysis revealed perspective errors in the sagittal and transverse planes. Finally, we measured only lower limb kinematics. Further research is needed to investigate the effects of MAS on kinetic information (electromyography and ground reaction force) during stair descent according to the severity of PFP while resolving sex differences.

CONCLUSIONS

PFP could be a contributing factor to the development of DKV during stair descent. In this study, DKV was significantly reduced when MAS was applied during stair descent. Moreover, participants who had a greater navicular drop distance showed greater improvement in DKV when MAS was applied. These findings indicate that clinicians can apply MAS to manage knee joint malalignment during stair descent, especially for individuals with a large navicular drop distance.

ACKNOWLEDGEMENTS

None.

FUNDING

None to declare.

CONFLICTS OF INTEREST

No potential conflict of interest relevant to this article was reported.

AUTHOR CONTRIBUTIONS

Conceptualization: HY, OK. Data curation: DL, IA. Formal analysis: DL, IA. Investigation: HY, IA. Methodology: HY, SJ, OK. Project administration: IA. Supervision: SJ, OK. Validation: OK. Visualization: DL. Writing - original draft: HY. Writing- review & editing: HY, SJ, OK.

Fig 1.

Figure 1.Medial arch support application.
Physical Therapy Korea 2022; 29: 208-214https://doi.org/10.12674/ptk.2022.29.3.208

Fig 2.

Figure 2.Measurement of the navicular drop distance. (A) Sitting position, (B) standing position.
Physical Therapy Korea 2022; 29: 208-214https://doi.org/10.12674/ptk.2022.29.3.208

Fig 3.

Figure 3.Measurement of the frontal plane projection angle during stair descent.
Physical Therapy Korea 2022; 29: 208-214https://doi.org/10.12674/ptk.2022.29.3.208

Fig 4.

Figure 4.The difference in the FPPAs with and without MAS application. FPPA, frontal plane projection angle; MAS, medial arch support. *p < 0.05.
Physical Therapy Korea 2022; 29: 208-214https://doi.org/10.12674/ptk.2022.29.3.208

Table 1 . Correlation coefficient between the navicular drop distance and changes in the FPPA when MAS was applied.

VariableChange in FPPA

rp
Navicular drop distance (mm)0.4530.045*

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