Effect of 3D printed foot orthoses stiffness and design on foot kinematics and plantar pressures in healthy people

Exploring the relationship between the supination resistance test and the effects of foot orthoses on the foot and ankle biomechanics during walking

BACKGROUND

The effects of foot orthoses on lower limb biomechanics during walking have been studied extensively. However, the lack of knowledge regarding the effects of various foot orthoses models for the same population complicates model selection in clinical practice and research. Additionally, there is a critical need to enhance our ability to predict the outcomes of foot orthoses using clinical tests, such as the supination resistance test.

RESEARCH QUESTION

What are the effects of two commonly prescribed types of FO (thin-flexible and medially wedged) on lower limb biomechanics during gait? Is there a correlation on these effects with the results of the supination resistance test?

METHODS

Twenty-three participants with flat feet were enrolled in this cross-sectional descriptive study. Participants underwent walking trials under three conditions: shod, thin-flexible FOs and medially wedged FOs. Midfoot, ankle, knee and hip angles, moments were calculated. Repeated measure ANOVAs were employed for within-group comparison across conditions. Correlations between the effects of FOs on foot and ankle angles/moments and supination resistance were determined using regression analyses using a statistical parametric mapping approach.

RESULTS

Thin-flexible and medially wedged FOs reduced midfoot dorsiflexion angles and ankle inversion moments. Medially wedged FOs also decreased midfoot and ankle abduction angles, midfoot plantarflexion moments compared to thin-flexible FOs and shoes. Moderate to good correlations between the supination resistance test and the medially wedged FOs were observed for the frontal and transverse ankle angles and moments.

SIGNIFICANCE

Medially wedged FOs are more effective in modifying lower limb biomechanics during walking compared to thin-flexible FOs. Greater supination resistance was associated with more pronounced effects for medially wedged FOs on foot and ankle biomechanics. These findings hold promise for refining orthotic prescription strategies, potentially offering advantages to individuals with musculoskeletal disorders.

Flatfoot arch correction with generic 3D-printed orthoses at different body weight percentages

BACKGROUND

Flatfoot can be associated with foot pathologies and treated conservatively with foot orthoses to correct arch collapse and alleviate painful symptoms. Recently, 3D printing has become more popular and is widely used for medical device manufacturing, such as orthoses. This study aims at quantifying the effect of generic 3D-printed foot orthoses on flatfoot arch correction under different static loading conditions.

METHODS

Participants with normal and flatfeet were recruited for this cross-sectional study. Clinical evaluation included arch height, foot posture index, and Beighton flexibility score. Surface imaging was performed in different loading conditions: 1) 0% when sitting, 2) 50% when standing on both feet, and 3) 125% when standing on one foot with a weighted vest. For flatfoot participants, three configurations were tested: without an orthosis, with a soft generic 3D printed orthosis, and with a rigid 3D printed orthosis. Arch heights and medial arch angles were calculated and compared for the different loading conditions and with or without orthoses. The differences between groups, with and without orthoses, were analyzed with Kruskal-Wallis tests, and a p < 0.05 was considered significant.

RESULTS

A total of 10 normal feet and 10 flatfeet were analyzed. The 3D printed orthosis significantly increased arch height in all loading conditions, compared to flatfeet without orthosis. Wearing an orthosis reduced the medial arch angle, although not significantly. Our technique was found to have good to excellent intra and interclass correlation coefficients.

CONCLUSIONS

Generic 3D printed orthoses corrected arch collapse in static loading conditions, including 125% body weight to simulate functional tasks like walking. Our protocol was found to be reliable and easier to implement in a clinical setting compared to previously reported methods.

LEVEL OF EVIDENCE

II.

Medially wedged foot orthoses generate greater biomechanical effects than thin-flexible foot orthoses during a unilateral drop jump task on level and inclined surfaces

BACKGROUND

Foot orthoses are therapeutic insoles designed to induce various effects on lower limb biomechanics. However, conflicting findings in previous research, highlight the need to better understand how foot orthoses with different features affect lower limb biomechanics during challenging tasks, particularly during unilateral drop jump landings.

METHODS

Seventeen participants with flat feet were recruited to participate in this cross-sectional descriptive study that examined the effects of thin-flexible foot orthoses and medially wedged foot orthoses on lower limb biomechanics during unilateral drop jump landings on level and valgus inclined surfaces. Midfoot, ankle, knee, and hip angles and moments were calculated and compared across conditions with repeated measures ANOVAs, using a statistical parametric mapping approach.

FINDINGS

Medially wedged and thin-flexible foot orthoses reduced ankle pronation and arch flattening during unilateral drop jump landings on level and valgus inclined surfaces. Medially wedged foot orthoses further decreased midfoot dorsiflexion and ankle eversion angles compared to thin-flexible foot orthoses. Medially wedged foot orthoses also generated greater effects on ankle kinetics and hip kinematics during unilateral drop jump landings.

INTERPRETATION

Medially wedged foot orthoses are more effective than thin-flexible foot orthoses in optimizing lower limb biomechanics during unilateral drop jump landings. While the biomechanical effects did not increase on inclined surfaces, medially wedged foot orthoses generated greater effects on proximal joints, highlighting their potential to improve hip stability and enhance overall lower limb function. Personalized foot orthoses selection based on specific biomechanical profiles should be further explored to optimize orthotic interventions benefiting individuals with musculoskeletal conditions.

3D Printing of Individual Running Insoles - A Case Study

Purpose

The study's starting point is to find a low-cost and best-fit solution for comfortable movement for a recreational runner with knee pain using an orthopedic device. It is a case study. The research aims to apply digitization, CAD/CAM tools, and 3D printing to create an individual 3D running insole. The objective is to incorporate flexible shape optimization would provide comfort reductions in foot plantar pressures in one subject with knee pain while running. The test hypothesis was if it is possible to make it from one material. For this purpose, we created a new digital workflow based on the Decision Tree method and analyzed pain and comfort scores during user testing of prototypes.

Patient and Methods

The input data were obtained during a professional examination by a specialist doctor in the orthopedic outpatient clinic in the motion laboratory (DIERS 4D Motion Lab, Germany) with the output of data on the proband's complex movement stereotype. Surface and volumetric data were obtained in the biomedical laboratory with the 3D scanner. We modified the digital 3D foot models in 3D mesh software, developed the design in SW Gensole (Gyrobot, UK), and finally incorporated the internal structure and the surface layer of the insole data of the knowledge from the medical examination, comfort analyses, and scientific studies findings.

Results

Four complete 3D-printed prototypes (n=4) with differences in density and correction elements were designed. All of them were fabricated on a 3D printer (Prusa i3 MK3S, Czech Republic) with flexible TPU material suitable for skin contact. The Participant tested each of them five times in the field during a workout and final insoles three months on the routine training.

Conclusion

A novel workflow was created for designing, producing, and testing full 3D-printed insoles. The product is fit for immediate use.

No Effect of EVA and TPU Custom Foot Orthoses on Mechanical Asymmetries during Acute Intense Fatigue

This study examined the impact of custom foot orthoses made of ethyl-vinyl acetate (EVA) and expanded thermoplastic polyurethane (TPU) materials, both compared to a control condition (CON; shoes only), on mechanical asymmetries during repeated treadmill sprints. Eighteen well-trained male runners executed eight, 5-s sprints (rest: 25 s) on an instrumented motorized treadmill in three footwear conditions (EVA, TPU, and CON). We evaluated the group mean asymmetry scores using the ‘symmetry angle’ (SA) formula, which assigns a score of 0% for perfect symmetry and a score of 100% for perfect asymmetry. There was no condition (all p ≥ 0.053) or time (p ≥ 0.074) main effects, nor were there any significant time × condition interactions on SA scores for any variables (p ≥ 0.640). Mean vertical, horizontal, and total forces presented mean SA values (pooled values for the three conditions) of 2.6 ± 1.9%, 2.9 ± 1.6%, and 2.4 ± 1.8%, respectively. Mean SA scores were ~1–3% for contact time (1.5 ± 0.5%), flight time (3.0 ± 0.3%), step frequency (1.1 ± 0.5%), step length (1.9 ± 0.7%), vertical stiffness (2.1 ± 0.9%), and leg stiffness (2.4 ± 1.1%). Mean SA scores were ~2–6.5% for duration of braking (4.1 ± 1.6%) and propulsive (2.4 ± 1.0%) phases, and peak braking (6.2 ± 2.9%) and propulsive (2.1 ± 1.4%) forces. In well-trained runners facing intense fatigue, wearing custom foot orthoses did not modify the observed low-to-moderate natural stride mechanical asymmetries.

Thick shells and medially wedged posts increase foot orthoses medial longitudinal arch stiffness: an experimental study

BACKGROUND

Foot orthoses (FOs) are commonly prescribed devices to attenuate biomechanical deficits and improve physical function in patients with musculoskeletal disorders. It is postulated that FOs provide their effects through the production of reaction forces at the foot-FOs interface. An important parameter to provide these reaction forces is their medial arch stiffness. Preliminary results suggest that adding extrinsic additions to FOs (e.g., rearfoot posts) increases their medial arch stiffness. A better understanding of how FOs medial arch stiffness can be modulated by changing structural factors is necessary to better customise FOs for patients. The objectives of this study were to compare FOs stiffness and force required to lower the FOs medial arch in three thicknesses and two models (with and without medially wedged forefoot-rearfoot posts).

METHODS

Two models of FOs, 3D printed in Polynylon-11, were used: (1) without extrinsic additions (mFO), and (2) with forefoot-rearfoot posts and a 6^o medial wedge (FO6MW). For each model, three thicknesses (2.6 mm, 3.0 mm, and 3.4 mm) were manufactured. FOs were fixed to a compression plate and vertically loaded over the medial arch at a rate of 10 mm/minute. Two-way ANOVAs and Tukey post-hoc tests with Bonferroni corrections were used to compare medial arch stiffness and force required to lower the arch across conditions.

RESULTS

Regardless of the differing shell thicknesses, the overall stiffness was 3.4 times greater for FO6MW compared to mFO (p < 0.001). FOs with 3.4 mm and 3.0 mm thicknesses displayed 1.3- and 1.1- times greater stiffness than FOs with a thickness of 2.6 mm. FOs with a thickness of 3.4 mm also exhibited 1.1 times greater stiffness than FOs with a thickness of 3.0 mm. Overall, the force to lower the medial arch was up to 3.3 times greater for FO6MW than mFO and thicker FOs required greater force (p < 0.001).

CONCLUSIONS

An increased medial longitudinal arch stiffness is seen in FOs following the addition of 6^o medially inclined forefoot-rearfoot posts, and when the shell is thicker. Overall, adding forefoot-rearfoot posts to FOs is significantly more efficient than increasing shell thickness to enhance these variables should that be the therapeutic aim.

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.

Do different multi-segment foot models detect the same changes in kinematics when wearing foot orthoses?

Background

Different multi-segment foot models have been used to explore the effect of foot orthoses. Previous studies have compared the kinematic output of different multi-segment foot models, however, no study has explored if different multi-segment foot models detect similar kinematic changes when wearing a foot orthoses. The aim of this study was to compare the ability of two different multi-segment foot models to detect kinematic changes at the hindfoot and forefoot during the single and double support phases of gait when wearing a foot orthosis.

Methods

Foot kinematics were collected during walking from a sample of 32 individuals with and without a foot orthosis with a medial heel bar using an eight-camera motion capture system. The Oxford Foot Model (OFM) and a multi-segment foot model using the Calibrated Anatomical System Technique (CAST) were applied simultaneously. Vector field statistical analysis was used to explore the kinematic effects of a medial heel bar using the two models, and the ability of the models to detect any changes in kinematics was compared.

Results

For the hindfoot, both models showed very good agreement of the effect of the foot orthosis across all three anatomical planes during the single and double support phases. However, for the forefoot, the level of agreement between the models varied with both models showing good agreement of the effect in the coronal plane but poorer agreement in the transverse and sagittal planes.

Conclusions

This study showed that while consistency exists across both models for the hindfoot and forefoot in the coronal plane, the forefoot in the transverse and sagittal planes showed inconsistent responses to the foot orthoses. This should be considered when interpreting the efficacy of different interventions which aim to change foot biomechanics.

The biomechanical effects of 3D printed and traditionally made foot orthoses in individuals with unilateral plantar fasciopathy and flat feet

BACKGROUND

Foot orthoses (FOs) are used to manage foot pathologies such as plantar fasciopathy. 3D printed custom-made FOs are increasingly being manufactured. Although these 3D-printed FOs look like traditionally heat-moulded FOs, there are few studies comparing FOs made using these two different manufacturing processes.

RESEARCH QUESTION

How effective are 3D-printed FOs (3D-Print) compared to traditionally-made (Traditional) or no FOs (Control), in changing biomechanical parameters of flat-footed individuals with unilateral plantar fasciopathy?

METHODS

Thirteen participants with unilateral plantar fasciopathy walked with shoes under three conditions: Control, 3D-print, and Traditional. 2 × 3 repeated measures analysis of variance (ANOVAs) with Bonferroni post-hoc tests were used to compare discrete kinematic and kinetic variables between limbs and conditions. Waveform analyses were also conducted using statistical parametric mapping (SPM).

RESULTS

There was a significant condition main effect for arch height drop (p = 0.01; ηp² =0.54). There was 0.87 mm (95% CI [-1.84, -0.20]) less arch height drop in 3D-print compared to Traditional. The SPM analyses revealed condition main effects on ankle moment (p < 0.001) and ankle power (p < 0.001). There were significant differences between control condition and both 3D-print and Traditional conditions. For ankle moment and power, there were no differences between 3D-print and Traditional conditions.

SIGNIFICANCE

3D-printed FOs are more effective in reducing arch height drop, whist both FOs lowered ankle plantarflexion moment and power compared to no FOs. The results support the use of 3D-printed FOs as being equally effective as traditionally-made FOs in changing lower limb biomechanics for a population of flat-footed individuals with unilateral plantar fasciopathy.

Effect of 3D printed foot orthoses stiffness on muscle activity and plantar pressures in individuals with flexible flatfeet: A statistical non-parametric mapping study

BACKGROUND

The 3D printing technology allows to produce custom shapes and add functionalities to foot orthoses which offers better options for the treatment of flatfeet. This study aimed to assess the effect of 3D printed foot orthoses stiffness and/or a newly design posting on muscle activity, plantar pressures, and center of pressure displacement in individuals with flatfeet.

METHODS

Nineteen individuals with flatfeet took part in this study. Two pairs of foot orthoses with different stiffness were designed for each participant and 3D printed. In addition, the flexible foot orthoses could feature an innovative rearfoot posting. Muscle activity, plantar pressures, and center of pressure displacement were recorded during walking.

FINDINGS

Walking with foot orthoses did not alter muscle activity time histories. Regarding plantar pressures, the most notable changes were observed in the midfoot area, where peak pressures, mean pressures and contact area increased significantly during walking with foot orthoses. The latter was reinforced by increasing the stiffness. Concerning the center of pressure displacement, foot orthoses shifted the center of pressure forward and medially at early stance. At the end of the stance phase, a transition of the center of pressure in posterior direction was observed during the posting condition. No effect of stiffness was observed on center of pressure displacement.

INTERPRETATION

The foot orthoses stiffness and the addition of posting influenced plantar pressures during walking. The foot orthoses stiffness mainly altered the plantar pressures under the midfoot area. However, posting mainly acted on peak and mean pressures under the rearfoot area.

Understanding the role of foot biomechanics on regional foot orthosis deformation in flatfoot individuals during walking

BACKGROUND

Foot orthoses (FOs) are one of the most common interventions to restore normal foot mechanics in flatfoot individuals. New technologies have made it possible to deliver customized FOs with complex designs for potentially better functionalities. However, translating the individuals' biomechanical needs into the design of customized FOs is not yet fully understood.

RESEARCH QUESTION

Our objective was to identify whether the deformation of customized FOs is related to foot kinematics and plantar pressure during walking.

METHODS

The kinematics of multi-segment foot and FOs contour were recorded together with plantar pressure in 17 flatfoot individuals while walking with customized FOs. The deformation of FOs surface was predicted from its contour kinematics using an artificial neural network. Plantar pressure map and deformation were divided into five anatomically based regions defined by the corresponding foot segments. Forward stepwise linear mixed models were built for each of the four gait phases to determine the feet-FOs interaction.

RESULTS

It was observed that some associations existed between foot kinematics and pressure with regional FOs deformation. From heel-strike to foot-flat, longitudinal arch angle was associated with FOs deformation in forefoot. From foot-flat to midstance, rearfoot eversion accounted for variation in the deformation of medial FOs regions, and forefoot abduction for the lateral regions. From midstance to heel-off, rearfoot eversion, longitudinal arch angle, and plantar pressure played significant role in deformation. Finally, from heel-off to toe-off, forefoot adduction affected the deformation of forefoot and midfoot.

SIGNIFICANCE

This study provides guidelines for designing customized FOs. Flatfoot individuals with excessive rearfoot eversion or very flexible medial arches require more support on medial FOs regions, while the ones with excessive forefoot abduction need the support on lateral regions. However, a compromise should be made between the level of support and the level of increase in plantar pressure to avoid stress on foot structures.

Anti-pronator components are essential to effectively alter lower-limb kinematics and kinetics in individuals with flexible flatfeet

BACKGROUND

Foot orthoses are commonly used to correct for foot alterations and especially address excessive foot pronation in individuals with flatfeet. In recent years, 3D printing has taken a key place in orthotic manufacturing processes as it offers more options and can be patient specific. Hence, the purpose of this study was to evaluate whether stiffness of 3D printed foot orthoses and a newly designed rearfoot posting have an effect on lower limb kinematics and kinetics in individuals with flatfeet.

METHODS

Nineteen patients with flexible flatfeet were provided two pairs of customized 3D printed ¾ length orthotics. Foot orthoses were of different stiffness and could feature a rearfoot posting, consisting of 2-mm carbon fiber plate. Lower limb kinematics and kinetics were computed using a multi-segment foot model. One-way ANOVAs using statistical non-parametric mapping, refined by effect sizes, were performed to determine the magnitude of the effect between conditions.

FINDINGS

Foot orthoses stiffness had little effect on midfoot and forefoot biomechanics. Reductions in midfoot eversion and forefoot abduction were observed during short periods of stance with rigid foot orthoses. Adding the posting had notable effects on rearfoot kinematics and on the ankle and knee kinetics in the frontal plane; it significantly reduced the eversion angle and inversion moment at the ankle, and increased the knee abduction moment.

INTERPRETATION

Using an anti-pronator component is more effective than increasing foot orthoses stiffness to observe a beneficial impact of foot orthoses on the control of excessive foot pronation in individuals with flatfeet.