Towards an efficient and robust foot classification from pedobarographic images

This paper presents a new computational framework for automatic foot classification from digital plantar pressure images. It classifies the foot as left or right and simultaneously calculates two well-known footprint indices: the Cavanagh's arch index (AI) and the modified AI. The accuracy of the framework was evaluated using a set of plantar pressure images from two common pedobarographic devices. The results were outstanding, as all feet under analysis were correctly classified as left or right and no significant differences were observed between the footprint indices calculated using the computational solution and the traditional manual method. The robustness of the proposed framework to arbitrary foot orientations and to the acquisition device was also tested and confirmed.     

Natural gaits of the non-pathological flat foot and high-arched foot

There has been a controversy as to whether or not the non-pathological flat foot and high-arched foot have an effect on human walking activities. The 3D foot scanning system was employed to obtain static footprints from subjects adopting a half-weight-bearing stance. Based upon their footprints, the subjects were divided into two groups: the flat-footed and the high-arched. The plantar pressure measurement system was used to measure and record the subjects' successive natural gaits. Two indices were proposed: distribution of vertical ground reaction force (VGRF) of plantar and the rate of change of footprint areas. Using these two indices to compare the natural gaits of the two subject groups, we found that (1) in stance phase, there is a significant difference (p<0.01) in the distributions of VGRF of plantar; (2) in a stride cycle, there is also a significant difference (p<0.01) in the rate of change of footprint area. Our analysis suggests that when walking, the VGRF of the plantar brings greater muscle tension to the flat-footed while a smaller rate of change of footprint area brings greater stability to the high-arched.     

Flat Feet,Happy Feet? Comparison of the Dynamic Plantar Pressure Distribution and Static Medial Foot Geometry between Malawian and Dutch Adults

In contrast to western countries, foot complaints are rare in Africa. This is remarkable, as many African adults walk many hours each day, often barefoot or with worn-out shoes. The reason why Africans can withstand such loading without developing foot complaints might be related to the way the foot is loaded. Therefore, static foot geometry and dynamic plantar pressure distribution of 77 adults from Malawi were compared to 77 adults from the Netherlands. None of the subjects had a history of foot complaints. The plantar pressure pattern as well as the Arch Index (AI) and the trajectory of the center of pressure during the stance phase were calculated and compared between both groups. Standardized pictures were taken from the feet to assess the height of the Medial Longitudinal Arch (MLA). We found that Malawian adults: (1) loaded the midfoot for a longer and the forefoot for a shorter period during roll off, (2) had significantly lower plantar pressures under the heel and a part of the forefoot, and (3) had a larger AI and a lower MLA compared to the Dutch. These findings demonstrate that differences in static foot geometry, foot loading, and roll off technique exist between the two groups. The advantage of the foot loading pattern as shown by the Malawian group is that the plantar pressure is distributed more equally over the foot. This might prevent foot complaints.     

A Dynamic Finite Element Analysis of Human Foot Complex in the Sagittal Plane during Level Walking

The objective of this study is to develop a computational framework for investigating the dynamic behavior and the internal loading conditions of the human foot complex during locomotion. A subject-specific dynamic finite element model in the sagittal plane was constructed based on anatomical structures segmented from medical CT scan images. Three-dimensional gait measurements were conducted to support and validate the model. Ankle joint forces and moment derived from gait measurements were used to drive the model. Explicit finite element simulations were conducted, covering the entire stance phase from heel-strike impact to toe-off. The predicted ground reaction forces, center of pressure, foot bone motions and plantar surface pressure showed reasonably good agreement with the gait measurement data over most of the stance phase. The prediction discrepancies can be explained by the assumptions and limitations of the model. Our analysis showed that a dynamic FE simulation can improve the prediction accuracy in the peak plantar pressures at some parts of the foot complex by 10%–33% compared to a quasi-static FE simulation. However, to simplify the costly explicit FE simulation, the proposed model is confined only to the sagittal plane and has a simplified representation of foot structure. The dynamic finite element foot model proposed in this study would provide a useful tool for future extension to a fully muscle-driven dynamic three-dimensional model with detailed representation of all major anatomical structures, in order to investigate the structural dynamics of the human foot musculoskeletal system during normal or even pathological functioning.     

An In Vivo Experimental Validation of a Computational Model of Human Foot

Reliable computational foot models offer an alternative means to enhance knowledge on the biomechanics of human foot.Model validation is one of the most critical aspects of the entire foot modeling and analysis process.This paper presents an invivo experiment combining motion capture system and plantar pressure measure platform to validate a three-dimensional finiteelement model of human foot.The Magnetic Resonance Imaging(MRI)slices for the foot modeling and the experimental datafor validation were both collected from the same volunteer subject.The validated components included the comparison of staticmodel predictions of plantar force,plantar pressure and foot surface deformation during six loading conditions,to equivalentmeasured data.During the whole experiment,foot surface deformation,plantar force and plantar pressure were recorded simultaneouslyduring six different loaded standing conditions.The predictions of the current FE model were in good agreementwith these experimental results.     

Triceps surae muscle-tendon unit length changes as a function of ankle joint angles and contraction levels: the effect of foot arch deformation

The purpose of this study was to clarify how foot deformation affects the relationship between triceps surae muscle-tendon unit (MTU) length and ankle joint angle. For six women and six men a series of sagittal magnetic resonance (MR) images of the right foot were taken, and changes in MTU length (the displacement of the calcaneal tuberosity), foot arch angle, and ankle joint angle were measured. In the passive session, each subject's ankle joint was secured at 10° dorsiflexed position, neutral position (NP), and 10° and 20° plantar flexed positions while MR images were acquired. In the active session, each subject was requested to perform submaximal isometric plantar flexions (30%, 60%, and 80% of voluntary maximum) at NP. The changes in MTU length in each trial were estimated by two different formulae reported previously. The changes of the measured MTU length as a function of ankle joint angles observed in all trials of the active session were significantly (p<0.05) larger than corresponding values in the passive session and by the estimation formulae. In the passive session, MTU length changes were significantly smaller than the estimated values when the ankle was plantar flexed. The foot arch angle increased as the contraction level increased from rest (117 ± 4°) to 80% (125 ± 3°), and decreased as the ankle was positioned further into plantar flexion in the passive session (115 ± 3°). These results indicate that foot deformation profoundly affects the triceps surae MTU length-ankle joint angle relationship during plantar flexion.     

Finite element modelling of radial shock wave therapy for chronic plantar fasciitis

Therapeutic use of high-amplitude pressure waves, or shock wave therapy (SWT), is emerging as a popular method for treating musculoskeletal disorders. However, the mechanism(s) through which this technique promotes healing are unclear. Finite element models of a shock wave source and the foot were constructed to gain a better understanding of the mechanical stimuli that SWT produces in the context of plantar fasciitis treatment. The model of the shock wave source was based on the geometry of an actual radial shock wave device, in which pressure waves are generated through the collision of two metallic objects: a projectile and an applicator. The foot model was based on the geometry reconstructed from magnetic resonance images of a volunteer and it comprised bones, cartilage, soft tissue, plantar fascia, and Achilles tendon. Dynamic simulations were conducted of a single and of two successive shock wave pulses administered to the foot. The collision between the projectile and the applicator resulted in a stress wave in the applicator. This wave was transmitted into the soft tissue in the form of compression–rarefaction pressure waves with an amplitude of the order of several MPa. The negative pressure at the plantar fascia reached values of over 1.5 MPa, which could be sufficient to generate cavitation in the tissue. The results also show that multiple shock wave pulses may have a cumulative effect in terms of strain energy accumulation in the foot.     

Three-dimensional finite element analysis of the foot during standing--a material sensitivity study

Information on the internal stresses/strains in the human foot and the pressure distribution at the plantar support interface under loading is useful in enhancing knowledge on the biomechanics of the ankle-foot complex. While techniques for plantar pressure measurements are well established, direct measurement of the internal stresses/strains is difficult. A three-dimensional (3D) finite element model of the human foot and ankle was developed using the actual geometry of the foot skeleton and soft tissues, which were obtained from 3D reconstruction of MR images. Except the phalanges that were fused, the interaction among the metatarsals, cuneiforms, cuboid, navicular, talus, calcaneus, tibia and fibula were defined as contact surfaces, which allow relative articulating movement. The plantar fascia and 72 major ligaments were simulated using tension-only truss elements by connecting the corresponding attachment points on the bone surfaces. The bony and ligamentous structures were embedded in a volume of soft tissues. The encapsulated soft tissue was defined as hyperelastic, while the bony and ligamentous structures were assumed to be linearly elastic. The effects of soft tissue stiffening on the stress distribution of the plantar surface and bony structures during balanced standing were investigated. Increases of soft tissue stiffness from 2 and up to 5 times the normal values were used to approximate the pathologically stiffened tissue behaviour with increasing stages of diabetic neuropathy. The results showed that a five-fold increase in soft tissue stiffness led to about 35% and 33% increase in the peak plantar pressure at the forefoot and rearfoot regions, respectively. This corresponded to about 47% decrease in the total contact area between the plantar foot and the horizontal support surface. Peak bone stress was found at the third metatarsal in all calculated cases with a minimal increase of about 7% with soft tissue stiffening.     

Ultrasound elastographic assessment of plantar fascia in runners using rearfoot strike and forefoot strike

Forefoot strike is increasingly being adopted by runners because it can better attenuate impact than rearfoot strike. However, forefoot strike may overload the plantar fascia and alter the plantar fascia elasticity. This study aimed to use ultrasound elastography to investigate and compare shear wave elasticity of the plantar fascia between rearfoot strikers and forefoot strikers. A total of 35 participants (21 rearfoot strikers and 14 forefoot strikers), who were free of lower limb injuries and diseases, were recruited from a local running club. Individual foot strike patterns were identified through the measured plantar pressure during treadmill running. The B-Mode ultrasound images and shear wave elastographic images of the plantar fascia were collected from each runner. Two independent investigators reviewed the images and examined the plantar fascia qualitatively and quantitatively. The results demonstrated an overall good agreement between the investigators in the image review outcomes (ICC:0.96–0.98, κ: 0.89). There were no significant differences in the fascial thickness (p = 0.50) and hypoechogenicity on the gray-scale images (p = 0.54) between the two groups. Shear wave elastography showed that forefoot strikers exhibited reduced plantar fascia elasticity compared to rearfoot strikers (p = 0.01, Cohen’s d = 0.91). A less elastic fascial tissue was more easily strained under loading. Tissue overstrain is frequently related to the incidence of plantar fasciitis. While further study is needed for firm conclusions, runners using forefoot strike were encouraged to enhance their foot strength for better protection of the plantar fascia.     

Foot arch deformation and plantar fascia loading during running with rearfoot strike and forefoot strike: A dynamic finite element analysis

Forefoot strike becomes popular among runners because it facilitates better impact attenuation. However, forefoot strike may overload the plantar fascia and impose risk of plantar fasciitis. This study aimed to examine and compare the foot arch deformation and plantar fascia tension between different foot strike techniques in running using a computational modelling approach. A three-dimensional finite element foot model was reconstructed from the MRI of a healthy runner. The foot model included twenty bones, bulk soft tissue, ligaments, tendons, and plantar fascia. The time-series data of segmental kinematics, foot muscle force, and ankle joint reaction force were derived from a musculoskeletal model of the same participant based on the motion capture analysis and input as the boundary conditions for the finite element analysis. Rearfoot strike and forefoot strike running were simulated using a dynamic explicit solver. The results showed that, compared to rearfoot strike, forefoot strike reduced the foot arch height by 9.12% and increased the medial longitudinal arch angle by 2.06%. Forefoot strike also increased the plantar connective tissues stress by 18.28–200.11% and increased the plantar fascia tensile force by 18.71–109.10%. Although it is currently difficult to estimate the threshold value of stress or force that results in injury, forefoot strike runners appeared to be more vulnerable to plantar fasciitis.     

Footprint analysis of gait using a pressure sensor system.

The purpose of this study was to investigate if the detailed pressure data of the footprints of normal gait add essential information to the spatio-temporal variables of gait. The gait of 62 healthy adult subjects was investigated using GAITRite pressure sensor system. Each footprint was divided into 12 equal trapezoids and after that the hindfoot, midfoot and forefoot analysis was developed. A typical activation pattern of the sensors with two peaks of active area and peak pressure distribution during normal walking was obtained. The first peak reflected the heel strike, and the second peak reflected push-off at the end of the stance phase. The lowest pressure values were in the midfoot, where the lateral part of the foot activated sensors more than the medial part. The footprint patterns of right and left legs were symmetrical and corresponded with the symmetry found in the spatio-temporal variables of gait. The variability for the active area and the peak pressure were more pronounced for the lateral part of the midfoot and a smaller variation was seen in areas with concentrated observations (e.g. 1st, 2nd and 5th lateral trapezoids). Increasing active area in the forefoot was associated with decreasing pressure sensor activity in the midfoot. The footprint patterns identified the symmetry between the legs and at the same time revealed the velocity performance.     

The relationship between plantar pressure and footprint shape

Fossil footprints preserve the only direct evidence of the external foot morphologies and gaits of extinct hominin taxa. However, their interpretation requires an understanding of the complex interaction among foot anatomy, foot function, and soft sediment mechanics. We applied an experimental approach aimed at understanding how one measure of foot function, the distribution of plantar pressure, influences footprint topography.     

Finite element modeling of the first ray of the foot: a tool for the design of interventions

Disorders of the first ray of the foot (defined as the hard and soft tissues of the first metatarsal, the sesamoids, and the phalanges of the great toe) are common, and therapeutic interventions to address these problems range from alterations in footwear to orthopedic surgery. Experimental verification of these procedures is often lacking, and thus, a computational modeling approach could provide a means to explore different interventional strategies. A three-dimensional finite element model of the first ray was developed for this purpose. A hexahedral mesh was constructed from magnetic resonance images of the right foot of a male subject. The soft tissue was assumed to be incompressible and hyperelastic, and the bones were modeled as rigid. Contact with friction between the foot and the floor or footwear was defined, and forces were applied to the base of the first metatarsal. Vertical force was extracted from experimental data, and a posterior force of 0.18 times the vertical force was assumed to represent loading at peak forefoot force in the late-stance phase of walking. The orientation of the model and joint configuration at that instant were obtained by minimizing the difference between model predicted and experimentally measured barefoot plantar pressures. The model were then oriented in a series of postures representative of push-off, and forces and joint moments were decreased to zero simultaneously. The pressure distribution underneath the first ray was obtained for each posture to illustrate changes under three case studies representing hallux limitus, surgical arthrodesis of the first ray, and a footwear intervention. Hallux limitus simulations showed that restriction of metatarsophalangeal joint dorsiflexion was directly related to increase and early occurrence of hallux pressures with severe immobility increasing the hallux pressures by as much as 223%. Modeling arthrodesis illustrated elevated hallux pressures when compared to barefoot and was dependent on fixation angles. One degree change in dorsiflexion and valgus fixation angles introduced approximate changes in peak hallux pressure by 95 and 22 kPa, respectively. Footwear simulations using flat insoles showed that using the given set of materials, reductions of at least 18% and 43% under metatarsal head and hallux, respectively, were possible.     

Free flap to the arteria peronea magna for lower limb salvage

A 36-year-old woman sustained an amputation of her right leg at the thigh level and a degloving injury of her left foot and ankle region in an accident during a suicide attempt. Primarily, her left foot was covered with a split skin graft, resulting in a soft-tissue defect at the medial malleolus and at the calcaneus bone. Reconstruction was planned with a free latissimus dorsi muscle flap. Preoperative examinations revealed an arteria peronea magna with a hyperplastic peroneal artery solely providing arterial blood supply to the foot. The arteria peronea magna divided into two branches proximal to the upper ankle joint, replacing the dorsal pedis artery and the medial plantar artery. Tibial posterior and tibial anterior arteries were hypoplastic-aplastic. Microvascular end-to-end anastomoses of the flap vessels to the medial branch ("medial plantar artery") of the arteria peronea magna and its concomitant vein at the medial malleolar bone level were successfully performed. The postoperative course was uneventful. Four weeks postoperatively, the patient started walking assisted by a prosthesis on her right thigh stump. This experience demonstrates that even in a case of arteria peronea magna, free flap surgery for lower limb salvage is a reliable and worthwhile method.     

A combined morphometric analysis of foot form and its association with sex,stature, and body mass

Objectives: Morphometric analysis of footprints is a classic means for orthopedic diagnosis. In forensics and physical anthropology, it is commonly used for the estimation of stature and body mass. We studied individual variation and sexual dimorphism of foot dimensions and footprint shape by a combination of classic foot measurements and geometric morphometric methods. Methods: Left and right feet of 134 healthy adult males and females were scanned twice with a 3D optical laser scanner, and stature as well as body mass were recorded. Foot length and width were measured on the 3D scans. The 2D footprints were extracted as the plantar‐most 2 mm of the 3D scans and measured with 85 landmarks and semilandmarks. Results: Both foot size and footprint shape are sexually dimorphic and relate to stature and body mass. While dimorphism in foot length largely results from dimorphism in stature, dimorphism in footprint shape partly owes to the dimorphism in BMI. Stature could be estimated well based on foot length (R² = 0.76), whereas body mass was more closely related to foot width (R² = 0.62). Sex could be estimated correctly for 95% of the individuals based on a combination of foot width and length. Discussion: Geometric morphometrics proved to be an effective tool for the detailed analysis of footprint shape. However, for the estimation of stature, body mass, and sex, shape variables did not considerably improve estimates based on foot length and width. Am J Phys Anthropol 157:582–591, 2015. © 2015 Wiley Periodicals, Inc.     

Dynamic plantar loading index: understanding the benefit of custom foot orthoses for painful pes cavus

The purpose of this study was to evaluate a new method showing how custom foot orthoses (CFO) improve dynamics of plantar loading. The method is based on the probability distribution of peak pressure time series and is quantified using the Regression Factor (RF). RF is a least square regression slope between the experimentally observed plantar pressure magnitude probability distribution and a modeled Gaussian shape. Plantar pressure data from a randomized controlled trial of 154 participants with painful Pes Cavus were retrospectively re-analyzed. The participants were randomized to an active treatment group given CFO or a control group given sham orthoses. The location of 2(nd) Peak pressure as a percentage of stance time (P(Loc2)) and its magnitude (P(M2)) was also calculated. In addition, plantar pressure data were collected on 23 healthy volunteers with normal foot alignment and no foot pain. Results demonstrated Pes Cavus had a significantly lower RF than healthy participants (0.30 v. 0.51; p<10(-7)). P(M2) was reduced in both active and control groups. However, RF and the P(Loc2) were only changed in the active group (p<0.005) without any significant change in the control group (p>0.5). This study suggests that painful Pes Cavus alters the shape of probability distribution of plantar loading during walking and CFO are an effective therapeutic solution that can significantly improve it. Further use of the RF index and 2(nd) peak pressure location as an outcome measure for treatment of foot and ankle deformities is suggested.     

Lateral facilitation of Hoffmann-reflexes prior to voluntary movement in a choice reaction time task.

Hoffmann reflexes (H reflexes) were elicited from both legs simultaneously in human subjects at varying intervals after a reaction signal (RS) in a binary choice reaction time task. A left light RS required a rapid plantar flexion of the left foot and a right light RS required a similar rapid response of the right foot. A large faciliataion of reflex amplitude occurred only in the muscle involved in the movement (right of left soleus). The timing of the facilitation indicated that a decision about the status of the RS occurred within 200 msec and probably was completed somewhat earlier. Furthermore, the facilitation of the H reflexes was shown to be closely linked with the organization required for the contractions of the responding muscle. The results are considered in the light of hypothesized mechanisms regulating voluntary movement.     

Reduction of plantar heel pressures: Insole design using finite element analysis

Plantar heel pain is a common condition that is often exacerbated by the repetitive stresses of walking. Treatment usually includes an in-shoe intervention designed to reduce plantar pressure under the heel by using insoles and a variety of off-the-shelf products. The design process for these products is often intuitive in nature and does not always rely on scientifically derived guidelines. Finite element analysis provides an efficient computational framework to investigate the performance of a large number of designs for optimal plantar pressure reduction. In this study, we used two-dimensional plane strain finite element modeling to investigate 27 insole designs. Combinations of three insole conformity levels (flat, half conforming, full conforming), three insole thickness values (6.3, 9.5 and 12.7 mm) and three insole materials (Poron Cushioning, Microcel Puff Lite and Microcel Puff) were simulated during the early support phase of gait. Plantar pressures predicted by the model were validated by experimental trials conducted in the same subject whose heel was modeled by loading the bare foot on a rigid surface and on foam mats. Conformity of the insole was the most important design variable, whereas peak pressures were relatively insensitive to insole material selection. The model predicted a 24% relief in pressure compared to barefoot conditions when using flat insoles; the reduction increased up to 44% for full conforming insoles.     

Predictors of Barefoot Plantar Pressure during Walking in Patients with Diabetes,Peripheral Neuropathy and a History of Ulceration

ObjectiveElevated dynamic plantar foot pressures significantly increase the risk of foot ulceration in diabetes mellitus. The aim was to determine which factors predict plantar pressures in a population of diabetic patients who are at high-risk of foot ulceration.MethodsPatients with diabetes, peripheral neuropathy and a history of ulceration were eligible for inclusion in this cross sectional study. Demographic data, foot structure and function, and disease-related factors were recorded and used as potential predictor variables in the analyses. Barefoot peak pressures during walking were calculated for the heel, midfoot, forefoot, lesser toes, and hallux regions. Potential predictors were investigated using multivariate linear regression analyses. 167 participants with mean age of 63 years contributed 329 feet to the analyses.ResultsThe regression models were able to predict between 6% (heel) and 41% (midfoot) of the variation in peak plantar pressures. The largest contributing factor in the heel model was glycosylated haemoglobin concentration, in the midfoot Charcot deformity, in the forefoot prominent metatarsal heads, in the lesser toes hammer toe deformity and in the hallux previous ulceration. Variables with local effects (e.g. foot deformity) were stronger predictors of plantar pressure than global features (e.g. body mass, age, gender, or diabetes duration).ConclusionThe presence of local deformity was the largest contributing factor to barefoot dynamic plantar pressure in high-risk diabetic patients and should therefore be adequately managed to reduce plantar pressure and ulcer risk. However, a significant amount of variance is unexplained by the models, which advocates the quantitative measurement of plantar pressures in the clinical risk assessment of the patient.     

Parametric study of orthopedic insole of valgus foot on partial foot amputation

Orthopedic insole was important for partial foot amputation (PFA) to achieve foot balance and avoid foot deformity. The inapposite insole orthosis was thought to be one of the risk factors of reamputation for foot valgus patient, but biomechanical effects of internal tissues on valgus foot had not been clearly addressed. In this study, plantar pressure on heel and metatarsal regions of PFA was measured using F-Scan. The three-dimensional finite element (FE) model of partial foot evaluated different medial wedge angles (MWAs) (0.0°–10.0°) of orthopedic insole on valgus foot. The effect of orthopedic insole on the internal bone stress, the medial ligament tension of ankle, plantar fascia tension, and plantar pressure was investigated. Plantar pressure on medial heel region was about 2.5 times higher than that of lateral region based on the F-Scan measurements. FE-predicted results showed that the tension of medial ankle ligaments was the lowest, and the plantar pressure was redistributed around the heel, the first metatarsal, and the lateral longitudinal arch regions when MWA of orthopedic insole ranged from 7.5° to 8.0°. The plantar fascias maintained about 3.5% of the total load bearing on foot. However, the internal stresses from foot bones increased. The simulation in this study would provide the suggestion of guiding optimal design of orthopedic insole and therapeutic planning to pedorthist.