scholarly journals Novel Method to Evaluate Angular Stiffness of Prosthetic Feet From Linear Compression Tests

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Peter G Adamczyk ◽  
Michelle Roland ◽  
Michael E. Hahn
Keyword(s):  
Center Of Pressure ◽  
Linear Displacement ◽  
Rate Of Change ◽  
Compression Tests ◽  
Prosthetic Foot ◽  
Stiffness Properties ◽  
Prosthetic Feet ◽  
Predicted Values ◽  
Parametric Adjustment ◽  
Linear Compression

Lower limb amputee gait during stance phase is related to the angular stiffness of the prosthetic foot, which describes the dependence of ankle torque on angular progression of the shank. However, there is little data on angular stiffness of prosthetic feet, and no method to directly measure it has been described. The objective of this study was to derive and evaluate a method to estimate the angular stiffness of prosthetic feet using a simple linear compression test. Linear vertical compression tests were performed on nine configurations of an experimental multicomponent foot (with known component stiffness properties and geometry), which allowed for parametric adjustment of hindfoot and forefoot stiffness properties and geometries. Each configuration was loaded under displacement control at distinct pylon test angles. Angular stiffness was calculated as a function of the pylon angle, normal force, and center of pressure (COP) rate of change with respect to linear displacement. Population root mean square error (RMSE) between the measured and predicted angular stiffness values for each configuration of the multicomponent foot was calculated to be 4.1 N-m/deg, dominated by a bias of the estimated values above the predicted values of 3.8 ± 1.6 N-m/deg. The best-fit line to estimated values was approximately parallel to the prediction, with R2 = 0.95. This method should be accessible for a variety of laboratories to estimate angular stiffness of experimental and commercially available prosthetic feet with minimal equipment.

Parametric Evaluation of Hindfoot and Forefoot Properties and Their Effect on the Angular Stiffness of Prosthetic Feet

2012 ◽  
Author(s):  
Peter G. Adamczyk ◽  
Michelle Roland ◽  
Michael E. Hahn
Keyword(s):  
Stance Phase ◽  
Direct Calculation ◽  
Future Studies ◽  
Prosthetic Foot ◽  
Moment Arms ◽  
Walking Performance ◽  
Deformation Mechanics ◽  
Prosthetic Feet ◽  
Stiffness Characteristics ◽  
Parametric Adjustment

Prosthetic foot stiffness has been recognized as an important factor in optimizing the walking performance of amputees [1–3]. Commercial feet are available in a range of stiffness categories and geometries. The stiffness of linear displacements of the hindfoot and forefoot for several commercially available feet have been reported to be within a range of 27–68 N/mm [4] and 28–76 N/mm [5], respectively, but these values are most relevant only to the earliest and latest portions of stance phase, when linear compression or rebound naturally occur. In contrast, mid-stance kinetics are more related to the angular stiffness of the foot, which describes the ankle torque produced by angular progression of the lower limb over the foot during this phase. Little data is available regarding the angular stiffness of any commercially available feet. The variety of geometries between manufacturers and models of prosthetic feet makes a direct calculation of effective angular stiffness challenging due to changes in moment arms based on loading condition, intricacies of deformation mechanics of the structural components, and mechanical interaction between hindfoot and forefoot components. Thus, modeling the interaction between hindfoot stiffness, forefoot stiffness, and keel geometries and their combined effect on the angular stiffness of the foot may be a useful tool for correlating functional outcomes with stiffness characteristics of various feet. To understand how each of these factors affects angular stiffness, we developed a foot that can parametrically adjust each of these factors independently. The objective of this study was to mathematically model, design, and experimentally validate a prosthetic foot that has independent hindfoot and forefoot components, allowing for parametric adjustment of stiffness characteristics and keel geometry in future studies of amputee gait.

scholarly journals Analysis of Rollover Shape and Energy Storage and Return in Cantilever Beam-Type Prosthetic Feet

2014 ◽  
Author(s):  
Kathryn M. Olesnavage ◽  
Amos G. Winter
Keyword(s):  
Energy Storage ◽  
Cantilever Beam ◽  
Cross Section ◽  
Stance Phase ◽  
Center Of Pressure ◽  
Reaction Force ◽  
Heel Strike ◽  
Prosthetic Foot ◽  
Beam Type ◽  
Prosthetic Feet

This paper presents an analysis of the rollover shape and energy storage and return in a prosthetic foot made from a compliant cantilevered beam. The rollover shape of a prosthetic foot is defined as the path of the center of pressure along the bottom of the foot during stance phase of gait, from heel strike to toe off. This path is rotated into the reference frame of the ankle-knee segment of the leg, which is held fixed. In order to achieve correct limb loading and gait kinematics, it is important that a prosthetic foot both mimic the physiological rollover shape and maximize energy storage and return. The majority of prosthetic feet available on the market are cantilever beam-type feet that emulate ankle dorsiflexion through beam bending. In this study, we show analytically that a prosthetic foot consisting of a beam with constant or monotonically decreasing cross-section cannot replicate physiological rollover shape; the foot is either too stiff when the ground reaction force (GRF) acts near the ankle, or too compliant when the GRF acts near the toe. A rigid constraint is required to prevent the foot from over-deflecting. Using finite element analysis (FEA), we investigated how closely a cantilever beam with constrained maximum deflection could mimic physiological rollover shape and energy storage/return during stance phase. A constrained beam with constant cross-section is able to replicate physiological rollover shape with R2 = 0.86. The ratio of the strain energy stored and returned by the beam compared to the ideal energy storage and return is 0.504. This paper determines that there is a trade off between rollover shape and energy storage and return in cantilever beam-type prosthetic feet. The method and results presented in this paper demonstrate a useful tool in early stage prosthetic foot design that can be used to predict the rollover shape and energy storage of any type of prosthetic foot.

scholarly journals A reduced order computational model of a semi-active variable-stiffness foot prosthesis

2020 ◽  
Author(s):  
Michael McGeehan ◽  
Peter Adamczyk ◽  
Kieran Nichols ◽  
Michael Hahn
Keyword(s):  
Body Weight ◽  
Center Of Pressure ◽  
Reaction Force ◽  
Variable Stiffness ◽  
Performance Standard ◽  
Design Parameters ◽  
Compression Tests ◽  
Static Compression ◽  
Lumped Parameter ◽  
Contact Models

INTRODUCTION: Passive energy storage and return (ESR) feet are the current performance standard in lower limb prostheses. A recently developed semi-active variable-stiffness foot (VSF) prosthesis balances the simplicity of a passive ESR device with the adaptability of a powered design. The purpose of this study was to model and simulate the ESR properties of the VSF prosthesis. METHODS: The ESR properties of the VSF were modeled as a lumped parameter overhung beam. The overhung length is variable, allowing the model to exhibit variable ESR stiffness. Foot-ground contact was modeled using sphere-to-plane contact models. Contact parameters were optimized to represent the geometry and dynamics of the VSF and its foam base. Static compression tests and gait were simulated. Simulation outcomes were compared to corresponding experimental data. RESULTS: Stiffness of the model matched that of the physical VSF (R2: 0.98, RMSE: 1.37 N/mm). Model-predicted resultant ground reaction force (GRFR) matched well under optimized parameter conditions (R2: 0.98, RMSE: 5.3% body weight,) and unoptimized parameter conditions (R2: 0.90, mean RMSE: 13% body weight). Anterior-posterior center of pressure matched well with R2 > 0.94 and RMSE < 9.5% foot length in all conditions. CONCLUSIONS: The ESR properties of the VSF were accurately simulated under benchtop testing and dynamic gait conditions. These methods may be useful for predicting GRFR arising from gait with novel prostheses. Such data are useful to optimize prosthesis design parameters on a user-specific basis.

Characterizing adaptations of prosthetic feet in the frontal plane

2020 ◽  
Vol 44 (4) ◽  
pp. 225-233
Author(s):  
Michael Ernst ◽  
Björn Altenburg ◽  
Thomas Schmalz
Keyword(s):  
Energy Storage ◽  
Theoretical Model ◽  
Ankle Joint ◽  
Frontal Plane ◽  
Measured Data ◽  
Limb Amputation ◽  
Clinical Parameters ◽  
Mechanical Adaptation ◽  
Prosthetic Foot ◽  
Prosthetic Feet

Background: Energy-storage and return feet incorporate various design features including split toes. As a potential improvement, an energy-storage and return foot with a dedicated ankle joint was recently introduced allowing for easily accessible inversion/eversion movement. However, the adaptability of energy-storage and return feet to uneven ground and the effects on biomechanical and clinical parameters have not been investigated in detail. Objectives: To investigate the design-related ability of prosthetic feet to adapt to cross slopes and derive a theoretical model. Study design: Mechanical testing and characterization. Methods: Mechanical adaptation to cross slopes was investigated for six prosthetic feet measured by a motion capture system. A theoretical model linking the measured data with adaptations is proposed. Results: The type and degree of adaptation depends on the foot design, for example, stiffness, split toe or continuous carbon forefoot, and additional ankle joint. The model used shows high correlations with the measured data for all feet. Conclusions: The ability of prosthetic feet to adapt to uneven ground is design-dependent. The split-toe feet adapted better to cross slopes than those with continuous carbon forefeet. Joints enhance this further by allowing for additional inversion and eversion. The influence on biomechanical and clinical parameters should be assessed in future studies. Clinical relevance Knowing foot-specific ability to adapt to uneven ground may help in selecting an appropriate prosthetic foot for persons with a lower limb amputation. Faster and more comprehensive adaptations to uneven ground may lower the need for compensations and therefore increase user safety.

scholarly journals Conceptual Design of a New Multi-Component Test Bench for the Dynamic Characterization of Running Specific Prostheses

Proceedings ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 75 ◽  
Author(s):  
Nicola Petrone ◽  
Gianfabio Costa ◽  
Gianmario Foscan ◽  
Francesco Bettella ◽  
Gianluca Migliore ◽  
...  
Keyword(s):  
Test Bench ◽  
Reaction Force ◽  
Dynamic Characterization ◽  
Prosthetic Foot ◽  
Load Combination ◽  
Stiffness Properties ◽  
Component Test ◽  
Static And Dynamic Loads ◽  
Force Components

Stiffness properties of running specific prostheses (RSP) for Paralympic runners are fundamental in the selection of the optimal running prosthetic foot (RPF) for sprint and jump events, depending on the athlete’s anthropometry and characteristics. RPFs are J-shaped or C-shaped, clamped to the socket or the pylon of the prosthetic leg. The aim of this work was to develop a test bench suitable for the static and dynamic characterization of a running prosthetic feet (RPF). Based on the evidence that the ground reaction force components change their relative orientation to the pylon or socket during the stance, loads were resolved in the socket reference frame and a multi-component test bench was designed and constructed. Two perpendicular actuators can apply static and dynamic loads to the foot while contacting a surrogate ground inclined at different angles. The preliminary tests show how the alignment, load combination, and ground angle can affect RPF stiffness curves.

Influence of gait training and prosthetic foot category on external work symmetry during unilateral transtibial amputee gait

2013 ◽  
Vol 37 (5) ◽  
pp. 396-403 ◽  
Author(s):  
Vibhor Agrawal ◽  
Robert Gailey ◽  
Christopher O’Toole ◽  
Ignacio Gaunaurd ◽  
Adam Finnieston
Keyword(s):  
Repeated Measures ◽  
Gait Training ◽  
Third Party ◽  
External Work ◽  
Gait Dynamics ◽  
Prosthetic Foot ◽  
Negative Work ◽  
Level 3 ◽  
Prosthetic Feet ◽  
Level 2

Background:Prosthetic foot prescription guidelines lack scientific evidence and are concurrent with an amputee’s concurrent with an amputee’s Medicare Functional Classification Level (K-Level) and categorization of prosthetic feet.Objective:To evaluate the influence of gait training and four categories of prosthetic feet (K1, K2, K3, and microprocessor ankle/foot) on Symmetry in External Work for K-Level-2 and K-Level-3 unilateral transtibial amputees.Design:Randomized repeated-measures trial.Methods:Five K-Level-2 and five K-Level-3 subjects were tested in their existing prosthesis during Session 1 and again in Session 2, following 2 weeks of standardized gait training. In Sessions 3–6, subjects were tested using a study socket and one of four randomized test feet. There was an accommodation period of 10–14 days with each foot. Symmetry in External Work for positive and negative work was calculated at each session to determine symmetry of gait dynamics between limbs at self-selected walking speeds.Results:K-Level-2 subjects had significantly higher negative work symmetry with the K3 foot, compared to K1/K2 feet. For both subject groups, gait training had a greater impact on positive work symmetry than test feet.Conclusion:Higher work symmetry is possible for K-Level-2 amputees who are trained to take advantage of K3 prosthetic feet designs. There exists a need for an objective determinant for categorizing and prescribing prosthetic feet.Clinical relevanceFindings that gait training can influence symmetry of gait dynamics and that K-Level-2 amputees can achieve greater work symmetry with a K3 foot having a “J-shaped” ankle and heel-to-toe footplate could potentially impact prosthetic care and foot prescription by clinicians and reimbursement guidelines by third-party health-care payers.

Biomechanical Model Representing Energy Storing Prosthetic Feet

2010 ◽  
Author(s):  
Francy L. Sinatra ◽  
Stephanie L. Carey ◽  
Rajiv Dubey
Keyword(s):  
Motion Analysis ◽  
Lower Limb ◽  
Biomechanical Model ◽  
Body Segment ◽  
Prosthetic Foot ◽  
Biomechanical Models ◽  
Prosthetic Feet ◽  
Analysis System ◽  
Lower Limb Amputees ◽  
Metabolic Information

Previous studies have been conducted to develop a biomechanical model for a human’s lower limb. Amongst them, there have been several studies trying to quantify the kinetics and kinematics of lower-limb amputees through motion analysis [5, 10, 11]. Currently, there are various designs for lower-limb prosthetic feet such as the Solid Ankle Cushion Heel (SACH) from Otto Bock (Minneapolis) or the Flex Foot from Ossur (California). The latter is a prosthetic foot that allows for flexibility while walking and running. Special interest has been placed in recording the capabilities of these energy-storing prosthetic feet. This has been done through the creation of biomechanical models with motion analysis. In these previous studies the foot has been modeled as a single rigid-body segment, creating difficulties when trying to calculate the power dissipated by the foot [5, 20, 21]. This project studies prosthetic feet with energy-storing capabilities. The purpose is to develop an effective way of calculating power by using a biomechanical model. This was accomplished by collecting biomechanical data using an eight camera VICON (Colorado) motion analysis system including two AMTI (BP-400600, Massachusetts) force plates. The marker set that was used, models the foot using several segments, hence mimicking the motion the foot undergoes and potentially leading to greater accuracy. By developing this new marker set, it will be possible to combine the kinematic and kinetic profile gathered from it with previous studies that determined metabolic information. This information will allow for the better quantification and comparison of the energy storage and return (ES AR) feet and perhaps the development of new designs.

Effect of Walking Speed on Angular Stiffness and Roll-Over Shape of the Intact and Prosthetic Feet of Transtibial Amputees

2013 ◽  
Author(s):  
Michelle Roland ◽  
Peter G. Adamczyk ◽  
Michael E. Hahn
Keyword(s):  
Lower Limb ◽  
Stance Phase ◽  
Walking Speed ◽  
Plantar Flexor ◽  
Limb Function ◽  
Prosthetic Foot ◽  
Material Stiffness ◽  
Prosthetic Feet ◽  
Transtibial Amputees ◽  
Lower Limb Function

The calculated roll-over shape and respective radius of intact and prosthetic feet has been shown to be a useful measure of lower limb function during walking [1–2]. Hansen et al [3] reported that the roll-over radius, R, is constant over a range of speeds for the intact foot-ankle system. It may be assumed that the prosthetic foot R would also be constant with increased walking speed. Similarly, the angular stiffness of prosthetic feet is not likely to change with walking speed, as the material stiffness remains unchanged. However, the effective angular stiffness of the intact ankle may increase with the plantar flexor moment during the stance phase of gait, which typically increases in magnitude with walking speed.

scholarly journals Influence of Degradation Products on the Elastic Stiffness Properties of Porous Absorbable Scaffolds Made From Bioabsorbable Metals

2021 ◽  
Author(s):  
Jannik Bühring ◽  
Maximilian Voshage ◽  
Johannes Heinrich Schleifenbaum ◽  
Holger Jahr ◽  
Kai-Uwe Schröder
Keyword(s):  
Finite Element ◽  
Young’S Modulus ◽  
Degradation Products ◽  
Young's Modulus ◽  
Element Model ◽  
Elastic Stiffness ◽  
Porous Scaffolds ◽  
Compression Tests ◽  
Substrate Layer ◽  
Stiffness Properties

For orthopaedic applications, additive manufactured (AM) porous scaffolds made of absorbable metals like magnesium, zinc or iron are of particular interest. They do not only offer the potential to design and fabricate bio-mimetic or rather bone equivalent mechanical properties, they also do not need to be removed in further surgery. Located in a physiological environment, scaffolds made of absorbable metals show a decreasing Young’s modulus over time, due to product dissolution. For WE43 scaffolds, during the first days an increase of the smeared Young's modulus can be observed, which is mainly attributed to a forming substrate layer of degradation products on the struts surfaces. In this study the influence of degradation products on the stiffness properties of metallic scaffolds is investigated. For this, analytical calculations and finite element simulations are performed to study the influence of the substrate layer thickness and Young's modulus for single struts and for a new scaffold geometry with adapted polar f2cc,z unit cells. The finite element model is further validated by compression tests on AM scaffolds made from Zn1Mg. The results show, that even low thicknesses and Young's moduli of the substrate layer increases significantly the smeared Young's modulus under axial compression.

scholarly journals PCA-Based Identification of Built Environment Factors Reducing PM2.5 Pollution in Neighborhoods of Five Chinese Megacities

Atmosphere ◽  
2022 ◽  
Vol 13 (1) ◽  
pp. 115
Author(s):  
Ming Chen ◽  
Fei Dai
Keyword(s):  
Built Environment ◽  
Meteorological Factors ◽  
Principal Component ◽  
Rate Of Change ◽  
Key Factors ◽  
Environment Factors ◽  
Pollution Levels ◽  
Principal Factors ◽  
Predicted Values ◽  
The Relationship

Air pollution, especially PM2.5 pollution, still seriously endangers the health of urban residents in China. The built environment is an important factor affecting PM2.5; however, the key factors remain unclear. Based on 37 neighborhoods located in five Chinese megacities, three relative indicators (the range, duration, and rate of change in PM2.5 concentration) at four pollution levels were calculated as dependent variables to exclude the background levels of PM2.5 in different cities. Nineteen built environment factors extracted from green space and gray space and three meteorological factors were used as independent variables. Principal component analysis was adopted to reveal the relationship between built environment factors, meteorological factors, and PM2.5. Accordingly, 24 models were built using 32 training neighborhood samples. The results showed that the adj_R2 of most models was between 0.6 and 0.8, and the highest adj_R2 was 0.813. Four principal factors were the most important factors that significantly affected the growth and reduction of PM2.5, reflecting the differences in green and gray spaces, building height and its differences, relative humidity, openness, and other characteristics of the neighborhood. Furthermore, the relative error was used to test the error of the predicted values of five verification neighborhood samples, finding that these models had a high fitting degree and can better predict the growth and reduction of PM2.5 based on these built environment factors.

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