Influence of arch support heights on the internal foot mechanics of flatfoot during walking: A muscle-driven finite element analysis

Advancements in diabetic foot insoles: a comprehensive review of design, manufacturing, and performance evaluation

The escalating prevalence of diabetes has accentuated the significance of addressing the associated diabetic foot problem as a major public health concern. Effectively offloading plantar pressure stands out as a crucial factor in preventing diabetic foot complications. This review comprehensively examines the design, manufacturing, and evaluation strategies employed in the development of diabetic foot insoles. Furthermore, it offers innovative insights and guidance for enhancing their performance and facilitating clinical applications. Insoles designed with total contact customization, utilizing softer and highly absorbent materials, as well as incorporating elliptical porous structures or triply periodic minimal surface structures, prove to be more adept at preventing diabetic foot complications. Fused Deposition Modeling is commonly employed for manufacturing; however, due to limitations in printing complex structures, Selective Laser Sintering is recommended for intricate insole designs. Preceding clinical implementation, in silico and in vitro testing methodologies play a crucial role in thoroughly evaluating the pressure-offloading efficacy of these insoles. Future research directions include advancing inverse design through machine learning, exploring topology optimization for lightweight solutions, integrating flexible sensor configurations, and innovating new skin-like materials tailored for diabetic foot insoles. These endeavors aim to further propel the development and effectiveness of diabetic foot management strategies. Future research avenues should explore inverse design methodologies based on machine learning, topology optimization for lightweight structures, the integration of flexible sensors, and the development of novel skin-like materials specifically tailored for diabetic foot insoles. Advancements in these areas hold promise for further enhancing the effectiveness and applicability of diabetic foot prevention measures.

Effect of forefoot transverse arch stiffness on foot biomechanical response--based on finite element method

Background

The plantar vault, comprising the transverse and longitudinal arches of the human foot, is essential for impact absorption, elastic energy storage, and propulsion. Recent research underscores the importance of the transverse arch, contributing over 40% to midfoot stiffness. This study aimed to quantify biomechanical responses in the ankle-foot complex by varying the stiffness of the deep metatarsal transverse ligament (DTML).

Methods

Using CT image reconstruction, we constructed a complex three-dimensional finite element model of the foot and ankle joint complex, accounting for geometric complexity and nonlinear characteristics. The focus of our study was to evaluate the effect of different forefoot transverse arch stiffness, that is, different Young's modulus values of DTML (from 135 MPa to 405 MPa), on different biomechanical aspects of the foot and ankle complex. Notably, we analyzed their effects on plantar pressure distribution, metatarsal stress patterns, navicular subsidence, and plantar fascial strain.

Results

Increasing the stiffness of the DTML has significant effects on foot biomechanics. Specifically, higher DTML stiffness leads to elevate von Mises stress in the 1st, 2nd, and 3rd metatarsals, while concurrently reducing plantar pressure by 14.2% when the Young's modulus is doubled. This stiffening also impedes navicular bone subsidence and foot lengthening. Notably, a 100% increase in the Young's modulus of DTML results in a 54.1% decrease in scaphoid subsidence and a 2.5% decrease in foot lengthening, which collectively contribute to a 33.1% enhancement in foot longitudinal stiffness. Additionally, doubling the Young's modulus of DTML can reduce the strain stretch of the plantar fascia by 38.5%.

Conclusion

Preserving DTML integrity sustains the transverse arch, enhancing foot longitudinal stiffness and elastic responsiveness. These findings have implications for treating arch dysfunction and provide insights for shoe developers seeking to enhance propulsion.

Custom orthotic design by integrating 3D scanning and subject-specific FE modelling workflow

The finite element (FE) foot model can help estimate pathomechanics and improve the customized foot orthoses design. However, the procedure of developing FE models can be time-consuming and costly. This study aimed to develop a subject-specific scaled foot modelling workflow for the foot orthoses design based on the scanned foot surface data. Six participants (twelve feet) were collected for the foot finite element modelling. The subject-specific surface-based finite element model (SFEM) was established by incorporating the scanned foot surface and scaled foot bone geometries. The geometric deviations between the scaled and the scanned foot surfaces were calculated. The SFEM model was adopted to predict barefoot and foot-orthosis interface pressures. The averaged distances between the scaled and scanned foot surfaces were 0.23 ± 0.09 mm. There was no significant difference for the hallux, medial forefoot, middle forefoot, midfoot, medial hindfoot, and lateral hindfoot, except for the lateral forefoot region (p = 0.045). The SFEM model evaluated slightly higher foot-orthoses interface pressure values than measured, with a maximum deviation of 7.1%. These results indicated that the SFEM technique could predict the barefoot and foot-orthoses interface pressure, which has the potential to expedite the process of orthotic design and optimization.

Effects of plantar fascia stiffness on the internal mechanics of idiopathic pes cavus by finite element analysis: implications for metatarsalgia

Metatarsalgia occurring in individuals with pes cavus is typically associated with abnormal loading patterns in the forefoot resulting from structural alterations. Simultaneously, the frequent overstress of the plantar fascia (PF) caused by the persistence of this foot deformity may further exacerbate the chronic pain induced by metatarsal overload. We aimed to investigate and quantify the effects of PF stiffness on the internal biomechanics of pes cavus using a computational modelling approach. A patient-specific finite element model of the foot-ankle complex using the actual three-dimensional geometry of idiopathic pes cavus bones and soft tissues was reconstructed. A sensitivity study was conducted to evaluate the effects of varying elastic modulus (0-700 MPa) of the PF on the metatarsal stress distribution, and force transmission through the metatarsophalangeal (MTP) and tarsometatarsal (TMT) joints in the pes cavus. The results indicated that variations in PF stiffness led to stress redistribution in the metatarsal region. Peak stress gradually reduced with decreasing stiffness until the PF was released, eventually resulting in a reduction of 22.39% compared to the reference value of 350 MPa. Furthermore, adjusting the PF stiffness to twice the reference value (700 MPa) increased the contact forces through the TMT and MTP joints by up to 23% and 116%, respectively. The reduction of PF stiffness alleviated focal metatarsal loading, and therefore, surgical fascia release can be considered to alleviate metatarsalgia in patients with pes cavus.

Clinically useful finite element models of the natural ankle - A review

BACKGROUND

Biomechanical simulation of the foot and ankle complex is a growing research area but compared to simulation of joints such as hip and knee, it has been under investigated and lacks consistency in research methodology. The methodology is variable, data is heterogenous and there are no clear output criteria. Therefore, it is very difficult to correlate clinically and draw meaningful inferences.

METHODS

The focus of this review is finite element simulation of the native ankle joint and we will explore: the different research questions asked, the model designs used, ways the model rigour has been ensured, the different output parameters of interest and the clinical impact and relevance of these studies.

FINDINGS

The 72 published studies explored in this review demonstrate wide variability in approach. Many studies demonstrated a preference for simplicity when representing different tissues, with the majority using linear isotropic material properties to represent the bone, cartilage and ligaments; this allows the models to be complex in another way such as to include more bones or complex loading. Most studies were validated against experimental or in vivo data, but a large proportion (40%) of studies were not validated at all, which is an area of concern.

INTERPRETATION

Finite element simulation of the ankle shows promise as a clinical tool for improving outcomes. Standardisation of model creation and standardisation of reporting would increase trust, and enable independent validation, through which successful clinical application of the research could be realised.

3D-printed medial arch supports of varying hardness versus a prefabricated arch support on plantar pressure: A 1-month randomized crossover study in healthy volunteers

BACKGROUND

Foot orthoses are commonly used as a noninvasive treatment to relieve foot pain. The custom full-length insoles with various materials and designs have been studied for their effectiveness in reducing plantar pressure. However, few studies have been conducted with respect to custom medial arch support on the relationships between material hardness and measured plantar pressure and level of comfort.

OBJECTIVES

To evaluate the effects of the hardness of custom medial arch supports on plantar pressure and comfort perception.

STUDY DESIGN

Randomized crossover study.

METHODS

Two custom silicone medial arch supports of varying hardness (A and B) were fabricated using 3D printing technology and tested in 12 healthy volunteers against a commercially prefabricated arch support (C). The volunteers wore three medial arch supports in a random order, one month for each arch support with 3-4 days of washout period before wearing the next one. The plantar pressure was measured and analyzed according to each foot zone: forefoot, midfoot, and hindfoot, comparing before intervention, immediately after intervention, and 1 month after intervention. The comfort perception was assessed by collecting volunteer feedback with a questionnaire after using each medial arch support.

RESULTS

After 1-month intervention, both 3D-printed and prefabricated medial arch supports demonstrated significantly higher average pressure in the midfoot ( P < 0.001), whereas significantly lower average pressure in the forefoot ( P < 0.001) and hindfoot ( P = 0.014, 0.026, and 0.018 for A, B, and C, respectively), compared with those before intervention. There were no significant differences in plantar pressure distribution between the 3D-printed and prefabricated medial arch supports. However, the 3D-printed medial arch supports resulted in better comfort than the prefabricated arch support.

CONCLUSIONS

The material hardness had no apparent effect on plantar pressure distribution. The three medial arch supports showed reducing plantar heel pressure. Further research is needed to investigate the potential effect of 3D-printed silicone medial arch supports on reducing foot pain in patients.

Surrogate optimization of a lattice foot orthotic

BACKGROUND

Additive manufacturing enables to print patient-specific Foot Orthotics (FOs). In FOs featuring lattice structures, the variation of the cell's dimensions provides a locally variable stiffness to meet the therapeutic needs of each patient. In an optimization problem, however, using explicit Finite Element (FE) simulation of lattice FOs with converged 3D elements is computationally prohibitive. This paper presents a framework to efficiently optimize the cell's dimensions of a honeycomb lattice FO for flat foot condition.

METHODS

We built a surrogate based on shell elements whose mechanical properties were computed by the numerical homogenization technique. The model was submitted to a static pressure distribution of a flat foot and it predicted the displacement field for a given set of geometrical parameters of the honeycomb FO. This FE simulation was considered as a black-box and a derivative-free optimization solver was employed. The cost function was defined based on the difference between the predicted displacement by the model against a therapeutic target displacement.

RESULTS

Using the homogenized model as a surrogate significantly accelerated the stiffness optimization of the lattice FO. The homogenized model could predict the displacement field 78 times faster than the explicit model. When 2000 evaluations were required in an optimization problem, the computational time was reduced from 34 days to 10 hours using the homogenized model rather than explicit model. Moreover, in the homogenized model, there was no need to re-create and re-mesh the insole's geometry in each iteration of the optimization. It was only required to update the effective properties.

CONCLUSION

The presented homogenized model can be used as a surrogate within an optimization framework to customize cell's dimensions of honeycomb lattice FO in a computationally efficient manner.

Photocurable and elastic polyurethane based on polyether glycol with adjustable hardness for 3D printing customized flatfoot orthosis

Orthopedic insoles is the most commonly used nonsurgical treatment method for the flatfoot. Polyurethane (PU) plays a crucial role in the manufacturing of orthopedic insoles due to its high wear resistance and elastic recovery. However, preparing orthopedic insoles with adjustable hardness, high-accuracy, and matches the plantar morphology is challenging. Herein, a liquid crystal display (LCD) three-dimensional (3D) printer was used to prepare the customized arch-support insoles based on photo-curable and elastic polyurethane acrylate (PUA) composite resins. Two kinds of photo-curable polyurethanes (DL1000-PUA and DL2000-PUA) were successfully synthesized, and a series of fast-photocuring polyurethane acrylate (PUA) composite resins for photo-polymerization 3D printing were developed. The effects of different acrylate monomers on the Shore hardness, viscosity, and mechanical properties of the PUA composite resins were evaluated. The PUA-3-1 composite resin exhibited low viscosity, optimal hardness, and mechanical properties. A deviation analysis was conducted to assess the accuracy of printed insole. Furthermore, the stress conditions of the PUA composite resin and ethylene vinyl acetate (EVA) under the weight load of healthy adults were compared by finite element analysis (FEA) simulation. The results demonstrated that the stress of the PUA composite resin and EVA were 0.152 MPa and 0.285 MPa, and displacement were 0.051 mm and 3.449 mm, respectively. These results indicate that 3D-printed arch-support insole based on photocurable PUA composite resin are high-accuracy, and can reduce plantar pressure and prevent insoles premature deformation, which show great potential in the physiotherapeutic intervention for foot disorders.

Immediate effects of forefoot wedges on multi-segment foot kinematics during jogging in recreational runners with a symptomatic pronated foot

Background: Foot orthoses (FOs) have been used to alter lower limb kinematics and kinetics in pronated feet. A clear relationship between FOs' features, e.g., the amount of wedging and support, and the corresponding biomechanical responses is vital for the design and prescription of FOs. In this study, we sought to determine if changing the level of the forefoot wedge would cause a linear response in the multi-segment foot kinematics during jogging, and if this effect would be enhanced by an arch support. Methods: Ten pairs of 3D printed FOs with five levels of forefoot wedges and two levels of arch supports were tested on 12 recreational runners with a symptomatic pronated foot. Multi-segment foot kinematic data during jogging was measured using the Oxford Foot Model. Two-way ANOVAs were performed to examine the main effect of the forefoot wedge and arch support, as well as their interaction on peak joint angles. Statistical parametric mapping and paired-t tests were used to identify differences in the foot kinematic traces and the joint range of motion (ROM) between each FO and the control, respectively. Results: Linear main effects for the forefoot wedge level were found in the forefoot peak dorsiflexion, eversion and rearfoot peak dorsiflexion of jogging. FOs with a medial forefoot wedge caused an average of 2.5° reduction of the forefoot peak abduction during jogging. Furthermore, forefoot wedges showed an opposite effect on the sagittal ROM of the forefoot and rearfoot. Adding an arch support did not improve the kinematic performance of a forefoot wedge during jogging. Conclusion: This study highlights a linear dose-response effect of a forefoot wedge on forefoot kinematics during jogging, and suggests using a medial forefoot wedge as an anti-pronator component for controlling forefoot motion of a pronated foot.

Biomechanical Analysis of Foot–Ankle Complex during Jogging with Rearfoot Strike versus Forefoot Strike

Background and Aim. In order to reduce foot and ankle injuries induced by jogging, two-foot strike patterns, rearfoot strike (RFS), and forefoot strike (FFS), were adopted and compared. First, RFS jogging and FFS jogging were experimentally studied, so as to acquire kinematic and kinetic data, including foot strike angle, knee flexion angle, and ground reaction force (GRF). Then, a 3D finite element model of foot–ankle complex was reconstructed from the scanned 2D-stacked images. Biomechanical characteristics, including plantar pressure, stress of metatarsals, midfoot bone, calcaneus and cartilage, and tensile force of plantar fascia and ligaments, were obtained. The results showed that RFS jogging and FFS jogging had a similar change trend and a close peak value of GRF. Since possessing more momentum in the push stage and less momentum in the brake stage, FFS jogging could be in favor of a higher jogging speed. However, FFS jogging produced larger metatarsal stress in the 5th metatarsal and much larger tensile force of plantar fascia, which might cause metatarsal fracture and heel pain. While RFS jogging produced larger plantar pressure in the hindfoot area, larger calcaneus stress, and much larger tarsal navicular stress, which might cause heel tissue injury, calcaneus damage, and stress fracture of naviculocuneiform joint. In addition, talocrural and talocalcaneal joint cartilage could bear jogging loads, as the peak contact pressure were both small in RFS jogging and FFS jogging. Therefore, jogging with rearfoot or FFS pattern should be chosen according to the health condition of foot–ankle parts.

Modified Ni-Nail and C-Nail systems for intra-articular fractures of the calcaneus: A biomechancial study

OBJECTIVES

We have proposed a novel intramedullary nail (Ni-Nail) by incorporating a sustentaculum tali screw to improve the fixation stability of minimally invasive treatment for calcaneal fractures. This study aimed to evaluate the biomechanical characters of the Ni-Nail system and compare it with traditional C-Nail system.

METHODS

A finite element model of a Sanders type-IIIAB calcaneal fracture was reconstructed and fixed using two intramedullary nail systems, which was validated by a cadaver study. A vertical loading of 700 N was applied to the subtalar joint surfaces, and 525 N Achilles tendon tension was applied to the superior border of the Achilles tuberosity. The von Mises stresses and fracture displacements of both fixation models were evaluated.

RESULTS

The maximum von Mises stress of the screws of Ni-Nail and C-Nail were 27.92 MPa and 57.42 MPa, respectively, while that of the main nail were 67.44 MPa and 53.01 MPa. In addition, the maximum fracture displacement of the Ni-Nail was larger than that of C-Nail by 15.6% (0.37 mm vs.0.32 mm).

CONCLUSIONS

Our static simulation analysis showed that both Ni-Nail and C-Nail demonstrated similar biomechanical stability for calcaneal fixation. The Ni-Nail features a simple structure that is easier to operate and less traumatizing. Future studies may consider to further evaluate the clinical effectiveness by clinical trials and follow-ups.

Effects of arch support doses on the center of pressure and pressure distribution of running using statistical parametric mapping

Insoles with an arch support have been used to address biomechanical risk factors of running. However, the relationship between the dose of support and running biomechanics remains unclear. The purpose of this study was to determine the effects of changing arch support doses on the center of pressure (COP) and pressure mapping using statistical parametric mapping (SPM). Nine arch support variations (3 heights * 3 widths) and a flat insole control were tested on fifteen healthy recreational runners using a 1-m Footscan pressure plate. The medial-lateral COP (COPML) coordinates and the total COP velocity (COPVtotal) were calculated throughout the entirety of stance. One-dimensional and two-dimensional SPM were performed to assess differences between the arch support and control conditions for time series of COP variables and pressure mapping at a pixel level, respectively. Two-way ANOVAs were performed to test the main effect of the arch support height and width, and their interaction on the peak values of the COPVtotal. The results showed that the COPVtotal during the forefoot contact and forefoot push off phases was increased by arch supports, while the COP medial-lateral coordinates remained unchanged. There was a dose-response effect of the arch support height on peak values of the COPVtotal, with a higher support increasing the first and third valleys but decreasing the third peak of the COPVtotal. Meanwhile, a higher arch support height shifted the peak pressure from the medial forefoot and rearfoot to the medial arch. It is concluded that changing arch support doses, primarily the height, systematically altered the COP velocities and peak plantar pressure at a pixel level during running. When assessing subtle modifications in the arch support, the COP velocity was a more sensitive variable than COP coordinates. SPM provides a high-resolution view of pressure comparisons, and is recommended for future insole/footwear investigations to better understand the underlying mechanisms and improve insole design.

Finite element modelling for footwear design and evaluation: A systematic scoping review

Finite element modelling has become an efficient tool for an in-depth understanding of the foot, footwear biomechanics and footwear optimization. The aim of this paper was to provide an updated overview in relation to the footwear finite element (FE) analysis published since 2000. The paper will attempt to outline the main challenges and research gaps that need confronting in the further development of realistic and accurate models for clinical and industrial applications. English databases of the Web of Science and PubMed were used to search (‘finite element’ OR ‘FEA’ OR ‘computational model’) AND (‘shoe’ OR ‘footwear’) until 16 December 2021. Articles that conducted FE analyses on the whole foot and footwear structures were included in this review. Twelve articles met the eligibility criteria, and were grouped into three categories for further analysis, (1) finite element modelling of the foot and high-heeled shoes; (2) finite element modelling of the foot and boot; (3) finite element modelling of the foot and sports shoe. Even though most of the existing foot-shoe FE analyses were performed under certain simplifications and assumptions, they have provided essential contributions in identifying the mechanical response of the foot in casual or athletic footwear. Further to this, the results have provided information in relation to optimizing footwear design to enhance functional performance. Nevertheless, further simulations still present several challenges, including reliable data information for geometry reconstruction, the balance between accurate details and computational cost, accurate representations of material properties, realistic boundary and loading conditions, and thorough model validation. In addition, some research gaps in terms of the coverage of footwear design, the consideration of insole/orthosis and socks, and the internal and external validity of the FE design should be fully covered.

The Influence of Mattress Stiffness on Spinal Curvature and Intervertebral Disc Stress-An Experimental and Computational Study

Sleeping support systems can influence spinal curvature, and the misalignment of the spinal curvature can lead to musculoskeletal problems. Previous sleep studies on craniocervical support focused on pillow variants, but the mattress supporting the pillow has rarely been considered. This study used a cervical pillow and three mattresses of different stiffnesses, namely soft, medium, and hard, with an indentation load deflection of 20, 42, and 120 lbs, respectively. A novel electronic curvature measurement device was adopted to measure the spinal curvature, whereby the intervertebral disc loading was computed using the finite element method. Compared with the medium mattress, the head distance increased by 30.5 ± 15.9 mm, the cervical lordosis distance increased by 26.7 ± 14.9 mm, and intervertebral disc peak loading increased by 49% in the soft mattress environment. Considering that the pillow support may increase when using a soft mattress, a softer or thinner pillow is recommended. The head distance and cervical lordosis distance in the hard mattress environment were close to the medium mattress, but the lumbar lordosis distance reduced by 10.6 ± 6.8 mm. However, no significant increase in intervertebral disc loading was observed, but contact pressure increased significantly, which could cause discomfort and health problems.

Multi-fidelity surrogate modeling through hybrid machine learning for biomechanical and finite element analysis of soft tissues

Biomechanical simulation enables medical researchers to study complex mechano-biological conditions, although for soft tissue modeling, it may apply highly nonlinear multi-physics theories commonly implemented by expensive finite element (FE) solvers. This is a significantly time-consuming process on a regular computer and completely inefficient in urgent situations. One remedy is to first generate a dataset of the possible inputs and outputs of the solver in order to then train an efficient machine learning (ML) model, i.e., the supervised ML-based surrogate, replacing the expensive solver to speed up the simulation. But it still requires a large number of expensive numerical samples. In this regard, we propose a hybrid ML (HML) method that uses a reduced-order model defined by the simplification of the complex multi-physics equations to produce a dataset of the low-fidelity (LF) results. The surrogate then has this efficient numerical model and an ML model that should increase the fidelity of its outputs to the level of high-fidelity (HF) results. Based on our empirical tests via a group of diverse training and numerical modeling conditions, the proposed method can improve training convergence for very limited training samples. In particular, while considerable time gains comparing to the HF numerical models are observed, training of the HML models is also significantly more efficient than the purely ML-based surrogates. From this, we conclude that this non-destructive HML implementation may increase the accuracy and efficiency of surrogate modeling of soft tissues with complex multi-physics properties in small data regimes.

Workflow assessing the effect of Achilles tendon rupture on gait function and metatarsal stress: Combined musculoskeletal modeling and finite element analysis

Achilles tendon rupture (ATR) incidence has increased among badminton players in recent years. The foot internal stress was hard to obtain through experimental testing. The purpose of the current research is to develop a methodology that could improve the finite element model derived foot internal stress prediction for ATR clinical and rehabilitation applications. A subject-specific musculoskeletal model was combined with a 3D finite element model to predict the metatarsal stress. The 80% point during the push-off phase of walking was selected for the comparing between injured and uninjured sides. The surgical repaired Achilles tendon (AT) after 12 months was elongated by 5.5% than the uninjured tendon. At 80% point of stance phase, the ankle plantarflexion angle and AT force decreased by 39.6% and 21.9% on the injured side, respectively. The foot inversion degree increased by 22.9% and was accompanied by the redistribution of metatarsals von Mises stress. The stresses on the fourth and fifth metatarsals were increased by 59.5% and 85.9% on the injured side. The workflow is available to assess musculoskeletal disorders and obtain foot internal stress after ATR. The decreased ankle plantar flexor force may be affected by triceps surae muscle atrophy and weakened force transmission ability of elongated AT. The increased von Mises stress on fourth and fifth metatarsals accompanied by higher foot inversion may increase the ankle lateral sprain injury risk.

Different Design Feature Combinations of Flatfoot Orthosis on Plantar Fascia Strain and Plantar Pressure: A Muscle-Driven Finite Element Analysis With Taguchi Method

Customized foot orthosis is commonly used to modify foot posture and relieve foot pain for adult acquired flexible flatfoot. However, systematic investigation of the influence of foot orthotic design parameter combination on the internal foot mechanics remains scarce. This study aimed to investigate the biomechanical effects of different combinations of foot orthoses design features through a muscle-driven flatfoot finite element model. A flatfoot-orthosis finite element model was constructed by considering the three-dimensional geometry of plantar fascia. The plantar fascia model accounted for the interaction with the bulk soft tissue. The Taguchi approach was adopted to analyze the significance of four design factors combination (arch support height, medial posting inclination, heel cup height, and material stiffness). Predicted plantar pressure and plantar fascia strains in different design combinations at the midstance instant were reported. The results indicated that the foot orthosis with higher arch support (45.7%) and medial inclination angle (25.5%) effectively reduced peak plantar pressure. For the proximal plantar fascia strain, arch support (41.8%) and material stiffness (37%) were strong influencing factors. Specifically, higher arch support and softer material decreased the peak plantar fascia strain. The plantar pressure and plantar fascia loading were sensitive to the arch support feature. The proposed statistics-based finite element flatfoot model could assist the insole optimization and evaluation for individuals with flatfoot.

Finite Element Modelling of Planus and Rectus Foot Types for the Study of First Metatarsophalangeal and First Metatarsocuneiform Joint Contact Mechanics

Evaluating the contact mechanics of human joints is an important element in understanding the pathomechanics of orthopaedic diseases. Although physical testing is essential in the evaluation process, reliable computational models can augment these experiments by non-invasive predictions of biomechanical or surgical variables. The objective of this study was to perform verification of a framework for developing a medial forefoot finite element. Verification was conducted by comparing computational predictions to experimental measurements of first metatarsophalangeal and first metatarsocuneiform joint contact mechanics. A custom-built force-controlled cadaveric test-rig was used to derive measurements of contact pressure, force, and area. A quasi-static finite element was developed and driven under the same boundary and loading conditions. Calibration of cartilage moduli and mesh sensitivity analyses were performed. Mean errors in contact pressures, forces, and areas were 24%, 4%, and 40% at the first metatarsophalangeal joint and 23%, 12%, and 19% at the first Metatarsocuneiform joint, respectively. Verification of a medial forefoot finite element model development framework was presented and found to be within 30% for contact pressure and contact force of both joints. This study presents a method to verify and simulate realistic physiological loading to investigate orthopaedic diseases of the medial forefoot.

Arch-Support Induced Changes in Foot-Ankle Coordination in Young Males with Flatfoot during Unplanned Gait Termination

Objective: The efficacy of arch orthoses in posture adjustment and joint coordination improvement during steady-state gait is well documented; however, the biomechanical changes of gait sub-tasks caused by arch support (AS), especially during gait termination, are poorly understood. Hence, this study aimed to investigate how the acute arch-supporting intervention affects foot–ankle coordination and coordination variability (CV) in individuals with flatfoot during unplanned gait termination (UGT). Methods: Twenty-five male patients with flatfoot were selected as subjects participated in this AS manipulation study. A motion capture system was used for the collection of the metatarsophalangeal joint (MPJ) and ankle kinematics during UGT. MPJ-Ankle coordination and CV were quantified using an optimized vector coding technique during the three sub-phases of UGT. A paired-sample t-test from the one-dimensional statistical parametric mapping of one-dimensional was applied to examine the data significance. Results: Significant differences for the joint kinematics between non-arch-support (NAS) and AS were exhibited only in the MPJ transverse plane during the middle and later periods of UGT (p = 0.04–0.026). Frontal plane MPJ-ankle coordination under AS during stimulus delay significantly decreased from 177.16 ± 27.41° to 157.75 ± 32.54° compared with under NAS (p = 0.026); however, the coordination pattern had not changed. Moreover, no significant difference was found in the coupling angle variability between NAS and AS in three planes during sub-phases of UGT (all p > 0.5). Conclusions: The detailed intrinsic characteristic of AS induced acute changes in lower extremity segment coordination in patients with mild flatfoot has been recorded. This dataset on foot-ankle coordination characteristics during UGT is essential for explaining foot function and injury prediction concerning AS manipulation. Further studies are expected to reflect lower limb inter-joint coordination during gait termination through the long-term effects of AS orthoses.

Biomechanical comparison among five mid/hindfoot arthrodeses procedures in treating flatfoot using a musculoskeletal multibody driven finite element model

BACKGROUND AND OBJECTIVE

Mid/hindfoot arthrodesis could modify the misalignment of adult-acquired flatfoot and attenuate pain. However, the long-term biomechanical effects of these surgical procedures remain unclear, and the quantitative evidence is scarce. Therefore, we aimed to investigate and quantify the influences of five mid/hindfoot arthrodeses on the internal foot biomechanics during walking stance.

METHODS

A young participant with flexible flatfoot was recruited for this study. We reconstructed a subject-specific musculoskeletal multibody driven-finite element (FE) foot model based on the foot magnetic resonance imaging. The severe flatfoot model was developed from the flexible flatfoot through the attenuation of ligaments and the unloading of the posterior tibial muscle. The five mid/hindfoot arthrodeses simulations (subtalar, talonavicular, calcaneocuboid, double, and triple arthrodeses) and a control condition (no arthrodesis) were performed simultaneously in the detailed foot multibody dynamics model and FE model. Muscle forces calculated by a detailed multi-segment foot model and ground reaction force were used to drive the foot FE model. The internal foot loadings were compared among control and these arthrodeses conditions at the first and second vertical ground reaction force (VGRF) peak and VGRF valley instants.

RESULTS

The results indicated that the navicular heights in double and triple arthrodeses were higher than other surgical procedures, while the subtalar arthrodesis had the smallest values. Five mid/hindfoot arthrodeses reduced the peak plantar fascia stress compared to control. However, double and triple arthrodeses increased the peak medial cuneo-navicular joint contact pressures and peak foot pressures as well as the metatarsal bones stresses.

CONCLUSION

Although mid/hindfoot arthrodesis generally reduced the collapse of medial longitudinal arch and plantar fascia loading during the stance phase, the increased loading in the adjacent unfused joint and metatarsal bones for double and triple arthrodeses should be noted. These findings could account for some symptoms experienced by flatfoot patients after surgery, which may facilitate the optimization of surgical protocols.

A Three-Dimensional Printed Foot Orthosis for Flexible Flatfoot: An Exploratory Biomechanical Study on Arch Support Reinforcement and Undercut

The advancement of 3D printing and scanning technology enables the digitalization and customization of foot orthosis with better accuracy. However, customized insoles require rectification to direct control and/or correct foot deformity, particularly flatfoot. In this exploratory study, we aimed at two design rectification features (arch stiffness and arch height) using three sets of customized 3D-printed arch support insoles (R+U+, R+U-, and R-U+). The arch support stiffness could be with or without reinforcement (R+/-) and the arch height may or may not have an additional elevation, undercutting (U+/-), which were compared to the control (no insole). Ten collegiate participants (four males and six females) with flexible flatfoot were recruited for gait analysis on foot kinematics, vertical ground reaction force, and plantar pressure parameters. A randomized crossover trial was conducted on the four conditions and analyzed using the Friedman test with pairwise Wilcoxon signed-rank test. Compared to the control, there were significant increases in peak ankle dorsiflexion and peak pressure at the medial midfoot region, accompanied by a significant reduction in peak pressure at the hindfoot region for the insole conditions. In addition, the insoles tended to control hindfoot eversion and forefoot abduction though the effects were not significant. An insole with stronger support features (R+U+) did not necessarily produce more favorable outcomes, probably due to over-cutting or impingement. The outcome of this study provides additional data to assist the design rectification process. Future studies should consider a larger sample size with stratified flatfoot features and covariating ankle flexibility while incorporating more design features, particularly medial insole postings.