DEGREE PROJECT IN MEDICAL ENGINEERING, SECOND CYCLE, 30 CREDITS
STOCKHOLM, SWEDEN 2020
The effect of the shoe sole shape on Plantar Pressure distribution
GERALDINE EJIMADU
KTH ROYAL INSTITUTE OF TECHNOLOGY
SCHOOL OF ENGINEERING SCIENCES IN CHEMISTRY, BIOTECHNOLOGY AND HEALTH
Abstract
Patients affected by Diabetes Mellitus have reduced tactile sensitivity and atrophy of the small muscles in the foot, resulting in high-pressure points that may remain unnoticed. The increased pressure can cause micro-trauma leading to wounds.
Because of the Diabetes Mellitus, DFUs do not heal easily. Up to 25% of them will develop diabetic foot ulcers (DFU), and 25% of DFUs that do not heal ultimately result in amputation.
This Master Thesis will describe and gather results of a newly acquired large international collaborative EU project (EIT Health 2020-2022) between three universities and three companies across Europe. This collaborative group will be the first to tackle the Diabetic Foot Ulcers problem preventatively with an innovative shoe concept, with seven different apex settings, which can be easily modified to avoid ulcerations in different areas of the foot. As an initial pilot, this master thesis project focuses on the analysis of the plantar pressure distribution by using the innovative shoes DR Comfort based on the adjustable rocker profiles, used as a prototype for the prevention of the Diabetic Foot Ulcer (DFU) formation in patients affected by Diabetes.
This project captures the motion data of healthy people with different shoe soles while walking at different levels of speed and assess the values of the peak plantar pressure, with the use of the Pedar-X, a measuring system device for the in-shoe plantar pressure. The evaluation of the adjustable rocker profiles is made through the calculation and analysis of the significant differences and p-values in peak plantar pressure, as well as the analysis of the Mean Plantar Pressure (MMP).
The results of this study show a reduction (although not pronounced) of the areas that are more affected by DFU. This study cannot be generalized to diabetic patients since ethical approval has not yet been received.
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Sammanfattning
Patienter med DM har minskad taktil känslighet och atrofi i de små musklerna i foten, vilket resulterar i högatryckpunkter som kan för bli obemärkta. Det ökade trycket kan orsaka mikrotrauma som leder till sår. På grund av Diabetes Mellitus, läker inte DFU lätt. Upp till 25% av dem kommer att utveckla diabetiska fotsår (DFU), och 25% av DFU: er som inte läker leder slutligen till amputation.
Detta examensarbete kommer att beskriva och samla resultat från ett nyförvärvat stort internationellt EU-projekt (EIT Health 2020-2022) mellan tre universitet och tre företag i hela Europa. Denna samarbetsgrupp kommer att vara den första att förebygga problemet med diabetiska fotsår med ett innovativt skokoncept diabetiska fotsår med ett innovativt skokoncept.
De kommer utföras med sju olika inställningar som lätt kan modifieras för att undvika sår på olika områden i foten. Som en första pilot fokuserar detta examensarbete på analys av plantartryckfördelning genom att använda de innovativa DR Comfort- skorna baserade på de justerbara ”rocker”-profilerna, som används som en prototyp för att förebygga bildningen av Diabetic Foot Ulcer (DFU) hos patienter som drabbats av Diabetes.
Den här avhandlingen fångar rörelsen hos friska personer med olika skosulor medan de går i olika hastighet och analyserar värdena för det maximala plantartrycket med användning av pedar-x. Pedar-x är en mätanordning för plantorns tryck i skon.
Utvärderingen av de justerbara ”rocker”-profilerna gjordes genom beräkning och analys av de signifikanta skillnaderna i top plantartrycket samt analysen av plantartryckets maximala medelvärde (MMP).
Resultaten av denna studie visar en minskning (även om den inte betydlig) av de områden som mest drabbats av DFU. Denna studie kan inte generaliseras till diabetespatienter eftersom etiskt godkännande ännu saknas.
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3 Acknowledgements
I would like to thank my supervisor, Elena Gutierrez Farewick for letting me be a part of this very interesting project, and for sharing her knowledge with me. I thank the project group leader Xiaogai Li, for assisting me and for giving words of affirmation during the project course. I thank the Life Group members for encouraging me and praying for me. I thank my family for encouraging me and believing in me. Grazie!
Finally, I thank God for being by side in this time of research.
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The effect of the shoe sole on Plantar Pressure
distribution
Påverkan av skosulans utformning på Fotens Tryckfördelning
Degree Project in Medical Engineering Supervisor: Elena Gutierrez Farewick Reviewer: Xiaogai Li
KTH Royal Institute of Technology, Stockholm, Sweden
School of Engineering Sciences in Chemistry, Biotechnology and Health
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Table of Contents
1. Introduction ... 7
2. Methods ... 9
2.1 Participants and trials ... 9
2.2 Equipment ... 9
2.2.1 Adjustable rocker profile and the apex settings ... 9
2.2.2 Pedar-X ... 10
2.3 Data analysis……….11
2.3.1 Masking ... 11
2.3.2 Statistical analysis ... 12
3. Results ... 13
4. Discussion ... 20
4.1 Limitations and future studies ... 20
5. Conclusion ... 22
6. References ... 23
Background ... 25
References ... 43
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7 1. INTRODUCTION
According to recent studies, 25% of patients suffering from Diabetes Mellitus (DM) are also affected by Diabetic Foot Ulcers (DFUs), which eventually leads to the amputation of the affected foot [1]. The DM is the primary cause of the DFU formation; however, its complications are the determining factors. The diabetic neuropathy of the distal lower extremities is the main consequence of DM, and it is expressed in autonomic, motor and sensory; the symptoms of this disease, i.e., dry skin, callus, muscle atrophy and loss of protective feedback, precede the formation of ulcers. Other complications from DM are peripheral vascular disease (such as ischemia), which hinders the correct flowing of blood throughout the lower extremities, as well as limited joint mobility [2].
The DFUs are circularly shaped wounds surrounded by dry skin aspect on the sole surface of the foot (also anatomically known as the plantar aspect). The areas of highest risk of DFU formation are in metatarsal heads (MTHs) and the hallux, because of the higher pressure that takes place on those locations [3]. A worsening of this condition leads to severe deformations of the foot, deeply impacting the foot functions and causing abnormal values of peak plantar pressure over bony prominences during walking. The plantar pressure data has been recognized as an element of interest for the analysis and assessment of DM patients prone to develop DFUs [4], for elevated foot stress, trauma, and abnormal Peak Pressure (PP) values are the main causes for DFU.
The Maximum Mean pressure (MMP) is the highest average pressure value within a particular area of the foot plantar, and it provides the clinicians with an understanding of the typical pressure acting on that specific region during the walking cycle [4]. The peak plantar pressure is the highest pressure measured on the plantar surface of the foot, and it results from the action of Ground Reaction Force (GRF) on the contact area of the foot [5]. As a preventative solution for the DFU problem, it is recommended to reduce the PP to below 200KPa, and when not possible, the PP reduction should be at least 30% less in patients considered at risk of developing DFU [5]. To reduce the PP values, the force applied to the contact area must be reduced, or the contact area between the foot plantar surface and the footwear must be increased [5].
This reduction is currently achievable with the use of rocker profiles and custom- made insoles. The rocker profile is a mechanism used to roll the foot from heel strike to toe-off, by stiffening the foot joints motion. The rocker profile is used to shift the area of application of the GRF away from the higher risked areas. The parameters defining the roll-over shape of the rocker profile are the apex position and the apex angles, which can be altered to allow pressure reducing effects. The apex position is the point where the rocker starts on the longitudinal axis, and it is calculated as a percentage of the total shoe length. The apex angle is the angle between the longitudinal axis and the apex of the rocker profile [6].
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The current rocker profile solutions are usually custom made by removing the original outer sole of a shoe and adding new material. However, there is no standard quantification for the shape of the rocker profile. Therefore, the positive outcome of this type of product (or the lack of thereof) is solely based on the skills of the orthopedic shoe technician. Moreover, the current rocker profile solution is often temporary; eventually, changes in the foot structures after using such footwear, result in the decline of the rocker profile offloading power [7]. This limitation calls the need for a solution that changes the rocker parameters individually, without the intervention of a pedorthist.
The adjustable rocker profile allows the rocker shape to be modified with the simple use of a screwdriver. With this new design, it is possible for the patient to have direct access to different orientations and positions of the apex in one shoe [5]. This solution is an alternative to adjusting the shape of a fixed rocker profile, which would usually need special, expensive machinery and has a time-consuming process.
This project aims at analyzing and comparing the plantar pressure distribution and PP offloading at different levels of walking speed when using regular shoes and the DR Comfort prototype footwear implemented with the adjustable rocker profiles.
What we expect from previous studies is an overall offloading of the in-shoe plantar pressure allowed by the different apex settings, in particular at the metatarsal region;
the pressure relief at the medial forefoot and in the hallux is expected to be higher in rocker configurations with higher apex angles, whereas the lower apex angle settings is going to offload the lateral side of the forefoot [8]; the final expectation is that more proximal apex settings will not offload the hallux.
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9 2. METHODS
The project took place at the KTH MoveAbility Lab at KTH University in Stockholm.
Eight healthy subjects participated in the study. The inclusion criteria for the subject were: healthy, adult, male or female, wearing shoe size EU 42 or 43. For this lab test, only one pair of DR Comfort footwear with size EU 43. The plantar pressure data were recorded with the use of the Pedar-X system, while the subjects’ personal information was retrieved via the Novel Database light application. The methodology used in this project was inspired by the study done by Roy Reints et all. (2020) [8].
2.1 Participants and trials
Each subject was prepared for the testing by following the specific guidelines provided in the Pedar-X manual [7]. The Pedar-X box can be worn inside a belt fasted around the subject’s waist; meanwhile, the sensor insoles are inserted into the shoes of the subject, to acquire plantar pressure data [9]. Furthermore, the subjects were asked to walk on the Monark Medical treadmill at three different walking speeds: 4 km/h, which commonly corresponds to a low level of speed, 5 km/h as a medium speed, and 6 km/h, which represents a faster walking speed.
For the first trial, the subjects had to walk wearing their regular comfortable shoes;
successively, they had to walk wearing the DR Comfort footwear. The number of trials for each subject was 24, and the number of steps recorded for each trial was not fixed.
2.1.1 Specifications
The data acquired were sampled at 100 Hz. The Pedar-X system was zeroed anytime the shoes were removed from the subjects; moreover, the feet were offloaded before each trial, for calibration purposes. For analysis purposes, only the left step was taken into consideration, because of an inconvenience in the right rocker profile. The insoles configuration selected for the trials was Y-1969I-1984r-Sep19-100hz.
2.2 Equipment
2.2.1 The adjustable rocker profile and the apex settings
The adjustable rocker profile prototype shoe is a modification of the DR Comfort shoes, where the outer sole has been modified to accommodate an adjustable roll-over system. These special shoes consist of two rails integrated with the shoe sole, and two knobs screwed unto two tee nuts with a bolt so that the knobs can slide through the rails; one of the knobs is on the medial side of the foot and the second on the lateral side. This sliding system allows the positions of the knobs to be changed comfortably, after manually loosening the bolts with the help of a screwdriver. Furthermore, the two knobs determine the rocker profile, which apex is determined by an imaginary line that crosses the midpoint of both knobs. A strap in Velcro is stitched to the nose of the shoe to make the apex settings even more accessible [8].
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In this footwear, the selection of the apex positions depends on the location of the subject’s metatarsal joints (MTHs). Thus, three reference lines are determined on the foot surface (Figure 1). The first line crosses the mth1 and the mth5, and it is called
“0%line”, while the other two lines called the “5% line” and the “10 % line” represent their distance from the zero line respectively, which is 5% and 10% of the total shoe length from the 0% line [6]. The shoe length was 30.5 cm, corresponding to 1.5 cm and 3 cm of distance from the 5% line and the 10% line, respectively. The knobs can slide into different positions throughout the footwear sole; each knob is either on the medial side “M” or on the lateral side “L” of the footwear. Seven main apex settings configurations have been tested.
Figure 1. M0L0: Medial knob at 0% Lateral knob at 0%; M5L5: Medial knob at 5% Lateral knob at 5%, M10L10: Medial knob at 10% Lateral knob at 10%; M0L5: Medial knob at 0% Lateral knob at 5%, M10L5: Medial knob at 10% Lateral knob at 5%; M5L10: Medial knob at 5% Lateral knob at 10% [8].
2.2.2 Pedar-X
The Pedar-X is a measuring device that utilizes in-shoe capacitive sensors to measure the dynamic plantar pressure distribution, and it is used to monitor the local loads between the foot and the shoe. This system offers the ultimate versatility with its multiple standard features and operating modes, allowing the connection to the computer via optic fiber, USB cable, or Bluetooth [9, 10]. Furthermore, the Pedar-X includes a software platform for the acquisition and analysis of the pressure data. This software displays the schematic of the left and right sensor insoles (consisting of 99 sensor cells); each point pressure value is displayed by each sensor cell, as well as user- specified color scheme to graphically display the pressure acting on the foot plantar (Figure 2) [4].
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Figure 2. Pressure values/colors for each sensor cells (a) represented in 2D mode and (b) displayed in a plot (lower speed)
2.3 DATA ANALYSIS 2.3.1 Masking
In order to obtain clinically relevant information when analyzing plantar pressure data, it is important to divide the foot into anatomical regions of interest rather than examining the foot as a whole [11]. This method is commonly known as “masking” of the plantar aspect, where the plantar surface is divided into different regions.
The Pedar-X allows at most seven regions to be selected. According to Patakiet all(2011) [12, 13], there are few specific anatomically correct masks that have been created to reflect normal and healthy’ feet ( found in Figure 3), and that highlight the more proximal location of MTPJs 4 and 5, and the 4th and 5th toes. For each mask, the main parameters are calculated and displayed. Figure 3 below shows how the sensors were selected from each mask, taking into consideration only the areas of a high risk of DFU development.
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Figure 3. (a) Pedar-x masking for plantar pressure assessment: 1) left insole ; 2) right insole; 3) Hallux;
4) Phalanges; 5) lateral forefoot;6) central forefoot;7) medial forefoot (b) Mask used for plantar pressure assessment [12]
The calculations used to obtain PP values for analysis purposes, considers the highest value of a sensor in a mask (part of the pressure sensing sole) during a step [6]. The PP corresponds to one value of which the exact location (somewhere in the mask) and the time (which time point during stance phase) is unknown. The value reported is the mean of the peak pressures of the total number of steps recorded. The Maximum mean pressure (MMP) was obtained by calculating the average value within a mask for every timeframe in each step, and by finally determining the highest mean value of the total number of steps recorded [8].
2.3.2 Statistical analysis
Means and standard deviations were calculated for PP and MMP through Matlab R2019b software and Excel tools; the statistic test chosen was dependent because of pairwise comparison, and the level of significance was set at p<0.05. The selection order chosen for the apex settings was randomized to avoid the subject from experiencing fatigue.
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13 3. RESULTS
The participants had a mean age of 33 (±9.8) years, bodyweight of 79.3 (±11.2) Kg, and body height of 1.78 (±6.1) m.
Figure 4 depicts the mean ± 1 SD of PP values for all rocker settings, compared to the regular shoes in the regions considered at higher risk for ulceration. A significant difference of PP in each setting compared to the normal shoe is indicated with an asterisk. Figure 4 shows that at a slow speed, the hallux region does not have any significant difference relative to the control shoes (blue column called “Normal”), however the pressure increases in M0L5. The phalanges region (in the second graph) displays significant differences in apex settings M5L0, M5L5, M10L5, and M10L10, where the peak pressure is significantly lower.
(a) (b)
Figure 4. Significative pressure changes in peak pressure for each apex settings across the hallux region (a) and the phalanges region (b) for low speed.
The medial forefoot mask increased in pressure in settings M5L10, M0L0 and M0L5
(a) (b)
Figure 5. Significative pressure changes in peak pressure for each apex settings across the medial forefoot region (a) and the central forefoot region (b) for slow speed.
0 20 40 60 80 100 120 140 160 180 200
Peak Pressure (kPa)
Apex settings
Hallux
0 20 40 60 80 100 120
Peak Pressure (kPa)
Apex settings
Phalanges
* * * *
0 20 40 60 80 100 120 140 160 180
Peak Pressure(kPa)
Apex settings
Medial Forefoot
0 20 40 60 80 100 120 140 160 180 200
Peak Pressure(kPa)
Apex settings
Central Forefoot
*
* * *
14 In Figure 5, the central forefoot is significantly lower in PP than the control for settings M0L5, M5L0, M5L5, M10L5, while in Figure 6 the lateral forefoot region presents changes for M5L0, M5L5, M5L10, and M10L5.
Figure 6. Significative pressure changes in peak pressure for each apex settings across the lateral forefoot region for slow speed
Figures 7,8 and 9 describe the significant reductions at medium speed walking. The following graphs show no significant difference in PP values.
(a) (b)
Figure 7. Significant pressure changes in peak pressure for each apex settings across the hallux region (a) and the phalanges region (b) for medium speed
In the phalanx’s region (Figure 7 to the right), it can be noticed that all the apex settings present a slightly higher peak pressure than the regular shoe, particularly in M10L10, which also increases the hallux PP.
0 20 40 60 80 100 120 140
Peak Pressure (kPa)
Apex settings
Lateral Forefoot
* * * *
0 20 40 60 80 100 120 140 160 180 200
Peak Pressure(kPa)
Apex settings
Hallux
0 20 40 60 80 100 120
Peak Pressure(kPa)
Apex settings
Phalanges
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15 On the other hand, only significant difference can be found in the medial forefoot in setting (Figure 8). Moreover, the only significant difference can be found in the medial forefoot in setting M5L5.
(a) (b)
Figure 8. Relative pressure changes in peak pressure for each apex settings across the medial forefoot region (a) and the central forefoot region (b) for medium speed
Figure 8 shows how the PP on the central forefoot has increased in M0L0, M10L10, and M5L5; in the lateral foot mask, the PP at M5L5 shows a scarce increase.
Figure 9. Peak pressure significant difference in peak pressure for each apex settings across the lateral forefoot region for medium speed.
0 20 40 60 80 100 120 140 160 180
Peak Pressure(kPa)
Apex settings
Medial Forefoot
*
0 20 40 60 80 100 120 140 160 180 200
Peak Pressure(kPa)
Apex Settings
Central Forefoot
*
112 114 116 118 120 122 124
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PEAK PRESSURE (KPA)
APEX SETTINGS
Lateral Forefoot
Normal M0L0 M0L5 M5L0 M5L5 M5L10 M10L5 M10L10
16 The following graphs show the average values in PP during fast speed walking, in the various apex settings, compared to the regular shoes. In Figure 10, significant changes can be noticed in the hallux region, where the peak pressure reduces for M0L0 and M5L5 apex settings; significant differences can also be observed in the medial forefoot region for M0L0, M0L5 and M5L5 configurations (Figure 11)
(a) (b)
Figure10.Relative pressure changes in peak pressure for each apex settings across the hallux region (a) and the phalanges region (b) for fast speed.
(a) (b)
Figure 11. Relative pressure changes in peak pressure for each apex settings across the medial forefoot 0
20 40 60 80 100 120 140 160 180 200
Peak Pressure(kPa)
Apex settings
Hallux
* *
0 20 40 60 80 100 120 140
Peak Pressure(kPa)
Apex setting
Phalanges
0 20 40 60 80 100 120 140 160 180
Peak Pressure(kPa)
Apex settings
Medial Forefoot
* * *
150 151 152 153 154 155 156 157 158 159 160 161
Peak Pressure(kPa)
Apex settings
Central Forefoot
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Figure 12. Relative pressure changes in peak pressure for each apex settings across the lateral forefoot region for fast speed
The following graphs in Figure 13, describe the changes in percentage of the MMP relative to the control shoes at three different levels of speed. The variations in MMP below are reported in percentages, and the negative percentages represent the reduction in MMP.
For slow-paced walk, the largest MMP reduction is found in the phalanges and the hallux regions, however, the overall changes are not high. The peak reduction of more than 20% can be observed on the hallux in the apex settings M10L10. Although not as high, the phalanges have a 10% to 20% reduction of the maximum average pressure in all seven rocker configurations.
Figure 13. Relative Maximum mean pressure for each apex settings across the five higher risk areas at low speed.
0 20 40 60 80 100 120 140
Peak pressure(kPa)
Apex settings
Lateral Forefoot
-25 -20 -15 -10 -5 0
M0L0 M0L5 M5L0 M5L5 M5L10 M10L5 M10L10
MMP Changes %
Apex Settings
Hallux (3) Phalanges (4) Med.Foot (7) Cen. Foot (6) Lat. Foot (5)
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pressure floats between 5% and 20%.
The MMP changes in the hallux region show a scarce increase in the setting M0L0, however, the hallux is one of the main offloaded regions in the other apex settings. At the phalanges mask, the MMP values have an increase in M10L10 and M0L0 by approximately 10%. At the medial forefoot mask, all apex settings result in lower values compared to the control, except for M10L10 where the values increase. The other settings show that this region is offloaded by 20%.
The changes at the central and lateral forefoot are similar in percentage, both showing the same reduction by approximately 20% in setting M0L0.
Figure 14. Relative Maximum mean pressure for each apex settings across the five higher risk areas at medium speed.
Figure 15. Relative Maximum mean pressure for each apex settings across the five higher risk areas -30
-20 -10 0 10 20 30
M0L0 M0L5 M5L0 M5L5 M5L10 M10L5 M10L10
MMP Changes %
Apex Settings
Hallux (3) Phalanges (4) Med.Foot (7) Cen. Foot (6) Lat. Foot (5)
-30 -25 -20 -15 -10 -5 0 5 10 15
M0L0 M0L5 M5L0 M5L56 M5L10 M10L5 M10L10
MMP Changes %
Apex settings
Hallux (3) Phalanges (4) Med.Foot (7) Cen. Foot (6) Lat. Foot (5)
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At a faster pace (Figure 15), the MMP reduction presents higher peaks than the changes observed for slower and medium speeds. The hallux mask has the highest reduction of 25%, among all the foot regions in the settings M10L5. Furthermore, the MMP is reduced at the medial forefoot by 20% in M5L10 and M0L5. The lateral forefoot displays a small percentage of increase in MMP for settings M0L5, M5L10, and M10L10.
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4.DISCUSSION
This study was aimed at identification and evaluation of variations in plantar pressure by using the adjustable rocker profile shoe outsoles, with a particular focus on the areas at high risk of ulceration at different walking speeds.
At the hallux, there is no significant decrease in pressure at a slower pace. On the contrary, the hallux increases in PP in the setting M10L5, which would falsify the predictions from previous studies [8], claiming that larger apex angles such as M10L5 (or M5L0) offload the hallux region; this exception is caused by the particular anatomy of a foot, whereby the apex angle, although larger, is positioned too proximally. Moreover, the peak pressure at the hallux has a significant reduction during the fast-paced walk in settings M0L0 and an increase in settings M10L10, proving that a less proximal apex setting is able to offload the peak pressure at the hallux.
At lower speed, the medial forefoot PP does not change significantly, and it presents higher values in M5L10, M0L0, and M0L5. However, for faster pace, the medial forefoot results in larger PP offloading in M0L0, M0L5, and M5L5. For lower speeds, the central forefoot shows higher significant pressure reduction in M0L5, M5L0, M5L5and M10L5, which are positioned more centrally in the foot and consist of a higher apex angle. While at a faster pace, the central forefoot has an increase in PP, which can be reconducted to the position of the apex, where the rocking action of the knobs at the distal and medial position of the foot (5%) blocks the rocking action of the more proximally and laterally positioned knob (10%).
At slow speed, the lateral forefoot is offloaded in M10L5, M5L5, M5L10, and M5L0, satisfying the expectations from the previous studies [8]; however, at faster speeds the peak pressure in this region increases in the M5L10. Moreover, PP at the phalanges shows significant changes during the slower speed in settings M5L0, M5L5, M10L5, and M5L0, which is expected since the lateral knob in all the offloading settings is situated slightly proximally in position %5, allowing the rollover of the foot to release the PP in this region.
According to the subjects of this study, the different rocker configurations have been considered “uncomfortable and unstable”; in particular, the configuration M10L10 was defined as “very unstable”, inducing the subject to walk with shorter gait cycles, which could explain the lack of significant reduction. Configurations M0L5 and M10L5 were considered more comfortable and more stable among the other settings, reinforcing the claim that larger and smaller apex angles have an offloading effect in multiple regions of the foot. Furthermore, both, M5L5 and M5L0 have been described as “pushing the body forward”, as to compensate for a possible lack of propulsion during the stance of a diabetic patient, which could explain the larger PP offloading.
Moreover, all the subjects reported to “feel more stable” when walking at a higher speed compared to lower.
4.1 Limitations and future studies
During the testing and measuring of the PP values, different limitations have been encountered, which may have influenced the outcome of this study. Firstly, the number of steps used to calculate the average step varied between 5 and 12 because of the lower number of steps recorded for each trial in the effort of avoiding the subject from experiencing fatigue. Therefore, the average values obtained may have differed for a higher number of steps.
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21 Secondly, the tested footwear consisted solely of the rocker profile outsoles, and no costume made insoles were used, which may affect the pressure distribution. Due to a breakage found on one of the knobs of the right Dr Comfort shoe, only the data from the left steps were included in this study; this condition may have limited the testing of the shoe and the recording of the step pressure parameters, because of the rocker asymmetry generated by the broken shoe, which could ultimately affect the shape of the sole and the gait of the subject. Another factor that could have changed the outcome of this study was the use of subjects who wear different shoe sizes (EU 42, 43) and shapes. The available pair of Dr Comfort shoes with size 43 have been used by each test subject.
Other limitations related to the footwear is the weight of the shoe, which is larger than the weight of a regular shoe because of the integrated sliding mechanism, which can cause additional fatigue on the subject. Although this study focused on the plantar aspect areas at high risk of ulceration, future research should focus on the analysis of the effect of the shoe sole shape on the heel, and investigate the connection between the peak pressure at the heel and the other areas on the plantar surface. Furthermore, future studies should include the analysis of the energy cost while walking with the rocker profile shoes.
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5. CONCLUSION
From the results gathered, it is possible to observe that the expectations from previous studies have not been completely met in regard to the relationship between the apex angle and the areas at high risk of ulceration. It can also be noted that the reductions in PP and MMP are less in percentage than expected based on previous studies.
However, there are significant reductions of peak pressure in the regions at high risk of ulceration due to the use of the adjustable rocker profile.
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[10]Novelgmbh, (2020). Pedar – footwear pressure distribution measurement
[11] Ellis, S. J., Stoecklein, H., Yu, J. C., Syrkin, G., Hillstrom, H., & Deland, J. T. (2011).
The accuracy of an automasking algorithm in plantar pressure measurements. HSS journal: the musculoskeletal journal of Hospital for Special Surgery, 7(1), 57–63. https://
doi.org/10.1007/ s11420-010-9185-9
[12] van der Zwaard, B., Vanwanseele, B., Holtkamp, F., van der Horst, H., Elders, P., &
Menz, H. (2014). Variation in the location of the shoe sole flexion point influences plantar loading patterns during gait. Journal of Foot And Ankle Research, 7(1). doi: 10.1186/1757- 1146-7-20
[13] Pataky, T. C., Bosch, K., Mu, T., Keijsers, N. L., Segers, V., Rosenbaum, D., &
Goulermas, J. Y. (2011). An anatomically unbiased foot template for inter-subject plantar pressure evaluation. Gait&posture, 33(3), 418–422. https://doi.org/10.1016/ j.
gaitpost.2010.12.015
[14] Hutchins, S., Bowker, P., Geary, N., & Richards, J. (2009). The biomechanics and clinical efficacy of footwear adapted with rocker profiles--evidence in the literature. Foot (Edinburgh, Scotland), 19(3), 165–170. https://doi.org/10.1016/ j. foot.2009.01.001
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BACKGROUND CHAPTER Geraldine Ejimadu
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INDEX
BACKGROUND CHAPTER
1. DIABETIC FOOT ULCERS….………27 1.1Definition and causes………27 1.2The anatomy of the foot………...27 1.3Sensory, motor and autonomic neuropathy………...29 1.4DFU progression and localization………...30
2.PRESSURE………..………31
2.1Plantar Pressure assessment………31 2.2Specifications………..31 2.3Measurment systems……..………34 2.4Pressure offloading………...……….35 3.BIOMECHANICAL CHANGES ………..35 3.1Gait Changes……….35 4.PREVIOUS SOLUTIONS ………...37 4.1Rocker profiles………37 4.1.1Parameters which determine the rocker profile shape………38 4.2Adjustable Rocker profile prototype………..39 4.2.1Design of the adjustable rocker profile……….39
4.2.2 Results from previous studies……….40 REFERENCES………43
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1.DIABETIC FOOT ULCERS
1.1Definition and causes
The diabetic foot ulceration (DFU) is a complication affecting patients suffering from diabetes mellitus. More specifically, DFUs are largely caused by the most common complication of DM, which is the diabetic neuropathy of distal lower extremities. The worsening of the DFUs often results in the amputation on the foot [1] [3]. The major cause for the development of DFUs is the mechanical stress that is applied to the foot, it is thus important to have a substantial knowledge of the feet biomechanics, in order to prevent the formation or recurrence of ulcers, and to promote wound healing [23].
Figure 16. Diabetic Foot Ulcer.
1.2The anatomy of the foot
The foot is made of 26 irregularly shaped bones, 30 synovial joints, and more than 100 muscles, tendons, and ligaments. The synovial joints have to interact in conformity in order to achieve smooth movements [24]. The foot performs motions mostly at three main synovial joints, which are the talocrural, the subtalar, and the midtarsal joint (see Figure. 17).
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28 At a functionality level, the foot supports all the weight of a person while standing or moving, and it is capable of adapting to uneven surfaces and acts as a shock absorber when it goes in contact with the ground, while also absorbing the rotation at the lower extremity. The foot also receives frictional and reactional forces coming from the ground; finally, it provides propulsion for the body to move forward during walking [24].
The foot can be divided into hindfoot, midfoot, and forefoot (see Figure 17) [24]. The hindfoot, better known as rearfoot, is made of talus and calcaneus; the midfoot consists of navicular, cuneiforms, and the cuboid and the forefoot is containing metatarsals and phalanges [24].
The foot can move in three planes, respect to the rearfoot (where the subtalar joint is).
It can perform plantarflexion and dorsiflexion, and these motions can also be described as a combination of inversion abduction and dorsiflexion called supination and a combination of plantarflexion and inversion abduction, which is the pronation [23][24]. The subtalar and the midtarsal joints provide supination and pronation; the first metatarsophalangeal joint (MTPJ) includes the metatarsal head (MTH) and it moves with the lesser MTPJs in a sagittal plane to perform plantarflexion and dorsiflexion. The first MTPJ, together with the hallux, has a load-bearing function, because it acts as a lever and can carry almost all the person’s weight, when performing heel lifting for propulsion.
Figure 17. Foot synovial joints (a), foot joints in lateral view (b) and functional regions of the foot ©.
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1.3SENSORY, MOTORIC AND AUTONOMIC NEUROPATHY
Neuropathy is divided in sensory, autonomic and motoric. Sensory neuropathy causes reduction, or lack of vibrational sense and superficial sensitivity; also loss of perception of temperature and pain, which leads to a higher risk for trauma, and subsequently to the development of foot deformities, and finally, injuries and ulcerations. Lack of sensitivity can lead to local ischemic necrosis (because of constant pressure for a prolonged period of time), immediate injuries (given by short pressure over a short period of time), inflammatory autolysis of tissue (caused by pressure on already injured or inflamed location on foot plantar). Motoric neuropathy is caused by the involvement of motor nerves, which function is damaged by the disease.
Motoric neuropathy leads to small foot muscles weakness and hypotrophy and stiffness of the tendons in the lower extremities, paresis, loss of muscle self-reflexes, which consequently causes foot imbalance, leading to claw toe development (malposition of the toe) , as can be observed in Figure Figure1.6, a high arched foot as seen in Figure 161.5 [23]. Muscular atrophy is neurogenic, which means that it is the effect of denervation caused by sensor neuropathy, and it is caused by the replacement of normal foot plantar muscle by fat cells [34]. Suzuki et all (2000), associated this atrophy with fat cell infiltration and impaired metabolism [34].
Figure 18. Foot pathologies based on the arch height.
Autonomic neuropathy causes subcutaneous vascular paresis which causes dysfunctional sweating leading to lower humidification and cooling, which dries the foot skin out, increasing the exposure to injuries. This disease is accompanied by single or multiple joints and/or bone destruction and in its acute phase leads to feet deformities (Charcot’s foot in Figure 18, 19, and 20) [4]. Autonomic neuropathy causes other serious complications among which medial arterial sclerosis is associated with twice as much probability of developing foot ulceration and three times as much probability for the foot to be amputated [1, 3].
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Figure 19. Diabetic foot affected by peripheral neuropathy: muscular atrophy, foot deformity.
1.4DFU progression and localization
Diabetic Foot ulcers are circular shaped, surrounded by highly dry and callous skin (caused by the high-pressure load), which could be affected by erythema and coinfection [3]. According to Levin the stages of progression of the DFU start with the acute stage, where the foot is red, swallowing and overheated, which leads to infection;
the second stage is represented by fractures and overall changes in bones and joints, the third stage of the diabetic foots the deformities such as flat foot and late rocker bottom; finally the fourth stage is the formation of plantar foot lesion [4]. If untreated, the deepening of the ulcer causes the infection from the bones underneath (osteomyelitis); many amputations are due to osteomyelitis. The regions exposed to pressure during normal walking are the heel, the midfoot, MTH5, MTH4, MTH2, MTH1, and the hallux [1]. According to Weijers et al. (2003) [33], the metatarsal heads and the hallux are the high-risk areas where the DFU develops because of the higher pressures take place at those locations. A worse foot condition is the Charcot arthropathy, which causes sever deformations of the foot, deeply impacting the foot functions and causing high peak plantar pressure
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over bony prominence during walking. This condition often leads to amputation [23].
Figure 20. Charcot foot compared to healthy foot.
2.PRESSURE
The pressure is defined as force per unit area. The System International unit of force is the newton, and the SI unit of pressure is the pascal (defined as the pressure experienced when a force of 1 N is distributed over an area of 1 m2). Kilopascals or megapascals are the preferred units of measurement pressure values [2].
2.1Plantar pressure assessment
The plantar pressure data are critical to evaluate and manage patients affected by foot impairment caused by neurological and musculoskeletal disorders. The pressure measurement is determined by the ground reaction which is the resultant force applied under the foot during locomotion [2][23]. The net ground reaction force is made of 3 components, each of which acts in one specific direction: the fore-aft, medial-lateral, and vertical directions; the vertical pressure is the pressure that can be easily quantified by commercial measurement systems. To measure pressure a sensor platform is used [2]. The assessment of plantar pressure is used for gait analysis, for direct treatment options and for patient education. The variables to be considered when assessing the plantar pressure are the peak pressure, the average pressure, force and area.
2.1.1 Peak pressure
The peak pressure (PP) is the highest value recorded by one sensor element in the displayed frame for the left and right insole sensors. The PP is of importance to decide whether certain orthotics cushions are able to reduce the pressure values under specific areas of the foot plantar.
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The Peak Pressure is the result of the GRF interacting with the plantar foot surface [29].
𝑃𝑃 = GRF
Contact Area
The average pressure provides with the values of the typical pressure acting upon the foot during a gait cycle. The peak pressure plot can be observed in form of a matrix of pressure values, presented in different colors based on the amount of pressure on each specific location on foot plantar as shown in Figure 21. The plantar surface of the foot is divided into different regions of interest: hindfoot, midfoot and forefoot.
Figure 21. Plantar Pressure peak values[30].
The calculations used by Roy Reints et all (2020) [25] to obtain the PP values is to consider the highest value of a sensor in a mask (part of the pressure sensing sole) during a step. So, this is one value of which the exact location (somewhere in the mask) and the time (which time point during stance phase) is unknown. The value reported is the mean of the peak pressures of 12 steps.
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Area
The area is another important element in plantar pressure analysis, as it represents the contact surface between the plantar surface and the sensor. It is calculated as the sum of the areas of all loaded sensors in the frame [31].
A=ΣAi
The area can be represented as the areas beneath force-time curve and pressure-time curve, which are called integral areas and describe the amount of pressure and force applied overtime during contact of individuals with diabetes and peripheral neuropathy to assist in their understanding of potential sites of ulceration. To be able to observe both 3D pressure and area from initial contact to toe off, and subsequently to locate potential sites of ulceration in individuals with diabetes the use of software is necessary.
Mean pressure
Average pressure for each time frame, and it’s calculated by summing all the pressure values in one-time frame divided by the number of sensors [31].
pmean=𝛴𝐹𝑖
𝛴Ai=𝛴(𝑃𝑖∙𝐴𝑖)
𝛴Ai
Force-Time Integral
Sum of the force at each frame multiplied by the time per frame (Area under the force- time curve) [31].
𝑓𝑡𝑖 = ∫ 𝐹 ∙ 𝑑𝑡
2.2 Specifications
When selecting the system to measure pressure, specifications like resolution, sampling frequency, reliability and calibration must be considered. In order to have high resolution, a great number of sensors is necessary. Moreover, the resolution is also determined by the size of the sensor, as the pressure is determined by force and area.
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34 Depending on the size of the area considered the same amount of force can be higher on lower. For example, the amount of force applied on a child’s foot plantar results in a pressure that is higher than the pressure resulting if the same force was to be applied on an adult’s foot plantar. The resolution of the pressure measurement system becomes an important consideration for the clinician, since there is a large variation in the size of the metatarsal heads, hallux, and toes based on foot size [5].
Another important specification is the sampling frequency. The sampling frequency is defined as the number of samples measured by each sensor per second and is recorded in cycles per second or hertz. According to Mittlemeier and Morlock (1993) [10], the optimal sampling frequencies for the Pedar insole system is between 45 and 100 Hz during regular walking and 200Hz for higher speed activities. In order to obtain a correct measurement and increase the reliability of the pressure measurement, Hughes et al (1991)suggested that 3 to 5 walking trials are necessary, taking into account that exact replicability cannot be insured, given the system differences in each working trial [11]. Moreover, measurement reliability of different sensor systems (including systematic variations and errors) have been reported, in order to have a correct reliability of the system.
Finally, although the system could present high reliability, it is important to make sure that the measurement values obtained correspond to actual pressure and force measurements [2, 11].
2.Measurement systems
To obtain data that are significant for the assessment positive outcome, a discussion surrounding the choice among different pressure measurement systems has to take place, based on their limits and advantages. The two main types of pressure measurement systems are the platform system and the in-shoe system [2].
The platform device is a more traditional solution which provides greater resolution, thanks to its higher number of sensors, however the patients are required to walk for a considering period of time in order for the data collection to be satisfying [11]. For patients affected by diabetes and neuropathy this method could actually increase the possibility of plantar ulceration because of the high number of steps required, also differences in steps and pressure distribution can be observed given the difficulty for the patient to perform coordinate movements and difficulty contacting the platform, which leads to targeting, which is the alteration of the patients walking pattern in order for the patients to place the foot in contact with the platform, altering the pressure distribution on the plantar [12][2]. The in-shoe sole eliminates the problem of targeting, since the patient is not required to walk for a long time and information at the shoe-foot interface can be revealed to
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the clinicians since the sensing device is positioned inside the shoe. Other than that, in-shoe pressure sensing devices are useful to assess new types of foot wears and orthotics, which the clinician can modify, based on the patients’ necessities [2].
However, limitations related to in- shoe soles are the use of less amount of sensors resulting in a not as much high resolution; the risk of damage of the sensor in the effort of removing the soles out of the footwear, affecting the reliability of the measurement. Repetitive loading and the environment within the shoe can impact the validity of the measurement [12, 13].
2.4Pressure offloading
Previous studies have shown that in order to prevent foot ulcer recurrence and promote foot ulcer healing, offloading locations of high pressure in the foot plantar has to take place. This study results contribute to the design and selection of custom- made footwears and insoles for diabetic patients, which are pressure-improved [5].
The best clinical effect is obtained by the combination of pressure relief and footwear adherence. It can be observed a 60% reduction of DFU recurrence when the level of pressure is inferior to 200 kPa, and when the level of footwear adherence is more than 80%. Proper footcare and pressure reducing footwear, reduces the peak pressure below 200 kPa, or if not possible to do so, reducing it by 30% at least [29]. Since the in-shoe peak pressure limit is different in each individual, the threshold used in clinical footwear practice for offloading purposes is 200 kPa [5]. According to a study done by Fady S. Botros et all. the main feature that distinguish between healthy gait and diabetic patients affected by neuropathy is the high PPP of the hallux region caused by high pressure upon the big toe region during toe-off, leading to ulcer development [28]; furthermore an elevated PTI on the first metatarsal shows how the presence of DPN leads to increased cumulative effect of pressure over tune and ulcer development. This classification study was made by using dynamic pressure data, which demonstrates its advantage over static measurements.
3.BIOMECHANICAL CHANGES 3.1Gait changes
It is necessary to understand the foot biomechanics and morphology when designing offloading footwear to reduce plantar ulcer formation and thus avoid amputation in people with diabetes. In order to understand how a particular gait can increase the peak pressure spreading on the foot plantar, it is important to have a proper knowledge of a healthy and generic gait cycle patterns [23].
