Design of Customized, 3D Printed Prosthetic Feet Using the Lower Leg Trajectory Error Metric

Abstract The walking pattern and comfort of a person with lower limb amputation are determined by the prosthetic foot’s diverse set of mechanical characteristics. However, most design methodologies are iterative and focus on individual parameters, preventing a holistic design of prosthetic feet for a user’s body size and walking preferences. Here we refined and evaluated the lower leg trajectory error (LLTE) framework, a novel quantitative and predictive design methodology that optimizes the mechanical function of a user’s prosthesis to encourage gait dynamics that match their body size and desired walking pattern. Five people with unilateral below-knee amputation walked over-ground at self-selected speeds using an LLTE-optimized foot made of Nylon 6/6, their daily-use foot, and a standardized commercial energy storage and return (ESR) foot. Using the LLTE feet, target able-bodied kinematics and kinetics were replicated to within 5.2% and 13.9%, respectively, 13.5% closer than with the commercial ESR foot. Additionally, energy return and center of mass propulsion work were 46% and 34% greater compared to the other two prostheses, which could lead to reduced walking effort. Similarly, peak limb loading and flexion moment on the intact leg were reduced by an average of 13.1%, lowering risk of long-term injuries. LLTE-feet were preferred over the commercial ESR foot across all users and preferred over the daily-use feet by two participants. These results suggest that the LLTE framework could be used to design customized, high performance ESR prostheses using low-cost Nylon 6/6 material.

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Design and Preliminary Testing of a Prototype for Evaluating Lower Leg Trajectory Error as an Optimization Metric for Prosthetic Feet

Volume 5A: 40th Mechanisms and Robotics Conference ◽

10.1115/detc2016-60565 ◽

2016 ◽

Cited By ~ 2

Author(s):

Kathryn M. Olesnavage ◽

Amos G. Winter

Keyword(s):

Lower Leg ◽

Clinical Testing ◽

Trajectory Error ◽

Preliminary Testing ◽

Rigid Structure ◽

Prosthetic Foot ◽

Constant Stiffness ◽

Prosthetic Feet ◽

Future Work ◽

Novel Design

This work presents the design and preliminary testing of a prosthetic foot prototype intended for evaluating a novel design objective for passive prosthetic feet, the Lower Leg Trajectory Error (LLTE). Thus far, all work regarding LLTE has been purely theoretical. The next step is to perform extensive clinical testing. An initial prototype consisting of rotational ankle and metatarsal joints with constant rotational stiffness was optimized and built, but at 2 kg it proved too heavy to use in clinical testing. A new conceptual foot architecture intended to reduce the weight of the final prototype is presented and optimized for LLTE. This foot consists of a rotational ankle joint with constant stiffness of 6.1 N·m/deg, a rigid structure extending 0.08 m from the ankle-knee axis, and a cantilever beam forefoot with bending stiffness 5.4 N·m2. A prototype was built using machined delrin for the rigid structure, three parallel extension springs offset along a constant radius cam from a pin joint ankle, and machined nylon as the beam forefoot. In preliminary testing, it was determined that, despite efforts to minimize weight and size, this particular design was still too heavy and bulky as a result of the extension springs to be used in extensive clinical testing. Future work will focus on reducing the weight further by replacing linear extension springs with flexural elements before commencing with the clinical study.

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Multi-Keel Passive Prosthetic Foot Design Optimization Using the Lower Leg Trajectory Error Framework

10.1115/detc2021-67673 ◽

2021 ◽

Author(s):

Victor Prost ◽

Heidi V. Peterson ◽

Amos G. Winter

Keyword(s):

Low Cost ◽

Lower Leg ◽

International Standards ◽

Limb Amputation ◽

Average Error ◽

Static Tests ◽

Prosthetic Devices ◽

Trajectory Error ◽

Prosthetic Foot ◽

Prosthetic Feet

Abstract People with lower-limb amputation in low- and middle-income countries (LMICs) lack access to adequate prosthetic devices that would restore their mobility and increase their quality of life. This is largely due to the cost and durability of existing devices. Single-keel energy storage and return (ESR) prosthetic feet have recently been developed to provide improved walking benefits at an affordable cost in LMICs. These low-cost single-keel ESR feet were created using a novel design methodology, the lower leg trajectory error (LLTE) framework. The LLTE framework enables the optimization of the stiffness and geometry of a user’s prosthesis to match a target walking pattern. However, these low-cost single-keel ESR prostheses do not provide the required durability to fulfill the international standards organization (ISO) testing, which prevents their widespread use and adoption. In this work, we developed a multi-keel prosthetic foot parametric model, and extended the LLTE framework to include this multi-keel architecture and the durability requirements. This extended LLTE framework enabled the design of durable and low-cost multi-keel ESR prosthetic feet made of Nylon 6/6. Multi-keel foot designs were shown to provide 76% improved walking performance (lower LLTE values) compared with single-keel ESR designs. Load testing of prototype multi-keel feet validated the multi-keel constitutive model predictions used in the LLTE framework. The measured deflections of the prototypes under load were accurately described with an average error of 0.6 ± 0.4 mm (5.7 ± 4.2%). These multi-keel feet designed using the extended LLTE framework withstood ISO fatigue and static tests, validating their durability. Given their single-part 2D extruded geometries, multi-keel feet designed with the extended LLTE framework could be cost-effectively manufactured, providing affordable and durable high-performance prostheses that improves the mobility of LMIC users.

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Experimental Demonstration of the Lower Leg Trajectory Error Framework Using Physiological Data as Inputs

Journal of Biomechanical Engineering ◽

10.1115/1.4048643 ◽

2020 ◽

Vol 143 (3) ◽

Author(s):

Kathryn M. Olesnavage ◽

Victor Prost ◽

William Brett Johnson ◽

Matthew J. Major ◽

Amos G. Winter

Keyword(s):

Mechanical Design ◽

Lower Leg ◽

Physiological Data ◽

Vertical Position ◽

Trajectory Error ◽

Ankle Stiffness ◽

Rms Error ◽

Prosthetic Feet ◽

The Relationship ◽

Error Testing

Abstract While many studies have attempted to characterize the mechanical behavior of passive prosthetic feet to understand their influence on amputee gait, the relationship between mechanical design and biomechanical performance has not yet been fully articulated from a fundamental physics perspective. A novel framework, called lower leg trajectory error (LLTE) framework, presents a means of quantitatively optimizing the constitutive model of prosthetic feet to match a reference kinematic and kinetic dataset. This framework can be used to predict the required stiffness and geometry of a prosthesis to yield a desired biomechanical response. A passive prototype foot with adjustable ankle stiffness was tested by a unilateral transtibial amputee to evaluate this framework. The foot condition with LLTE-optimal ankle stiffness enabled the user to replicate the physiological target dataset within 16% root-mean-square (RMS) error. Specifically, the measured kinematic variables matched the target kinematics within 4% RMS error. Testing a range of ankle stiffness conditions from 1.5 to 24.4 N·m/deg with the same user indicated that conditions with lower LLTE values deviated the least from the target kinematic data. Across all conditions, the framework predicted the horizontal/vertical position, and angular orientation of the lower leg during midstance within 1.0 cm, 0.3 cm, and 1.5 deg, respectively. This initial testing suggests that prosthetic feet designed with low LLTE values could offer benefits to users. The LLTE framework is agnostic to specific foot designs and kinematic/kinetic user targets, and could be used to design and customize prosthetic feet.

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Design and Testing of a Prosthetic Foot With Interchangeable Custom Springs for Evaluating Lower Leg Trajectory Error, an Optimization Metric for Prosthetic Feet

Journal of Mechanisms and Robotics ◽

10.1115/1.4039342 ◽

2018 ◽

Vol 10 (2) ◽

Cited By ~ 1

Author(s):

Victor Prost ◽

Kathryn M. Olesnavage ◽

W. Brett Johnson ◽

Matthew J. Major ◽

Amos G. Winter

Keyword(s):

Range Of Motion ◽

Ankle Joint ◽

Large Scale ◽

Joint Stiffness ◽

Lower Leg ◽

Trajectory Error ◽

Prosthetic Foot ◽

Design Variables ◽

Prosthetic Feet

An experimental prosthetic foot intended for evaluating a novel design objective is presented. This objective, called the lower leg trajectory error (LLTE), enables the optimization of passive prosthetic feet by modeling the trajectory of the shank during single support for a given prosthetic foot and selecting design variables that minimize the error between this trajectory and able-bodied kinematics. A light-weight, fully characterized test foot with variable ankle joint stiffness was designed to evaluate the LLTE. The test foot can replicate the range of motion of a physiological ankle over a range of different ankle joint stiffnesses. The test foot consists of a rotational ankle joint machined from acetal resin, interchangeable U-shaped nylon springs that range from 1.5 N · m/deg to 24 N · m/deg, and a flexible nylon forefoot with a bending stiffness of 16 N · m2. The U-shaped springs were designed to support a constant moment along their length to maximize strain energy density; this feature was critical in creating a high-stiffness and high-range of motion ankle. The design performed as predicted during mechanical and in vivo testing, and its modularity allowed us to rapidly vary the ankle joint stiffness. Qualitative feedback from preliminary testing showed that this design is ready for use in large scale clinical trials to further evaluate the use of the LLTE as an optimization objective for passive prosthetic feet.

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Lower Leg Trajectory Error: A novel optimization parameter for designing passive prosthetic feet

2015 IEEE International Conference on Rehabilitation Robotics (ICORR) ◽

10.1109/icorr.2015.7281211 ◽

2015 ◽

Cited By ~ 3

Author(s):

Kathryn M. Olesnavage ◽

Amos G. Winter

Keyword(s):

Lower Leg ◽

Trajectory Error ◽

Optimization Parameter ◽

Prosthetic Feet

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Design and Testing of a Prosthetic Foot Prototype With Interchangeable Custom Rotational Springs to Adjust Ankle Stiffness for Evaluating Lower Leg Trajectory Error, an Optimization Metric for Prosthetic Feet

Volume 5B: 41st Mechanisms and Robotics Conference ◽

10.1115/detc2017-67820 ◽

2017 ◽

Author(s):

Victor Prost ◽

Kathryn M. Olesnavage ◽

Amos G. Winter

Keyword(s):

Optimization Method ◽

Lower Leg ◽

Trajectory Error ◽

Preliminary Testing ◽

Design Objective ◽

Rigid Structure ◽

Prosthetic Foot ◽

Constant Stiffness ◽

Ankle Stiffness ◽

Prosthetic Feet

A prosthetic foot prototype intended for evaluating a novel design objective for passive prosthetic feet, the Lower Leg Trajectory Error (LLTE), is presented. This metric enables the optimization of prosthetic feet by modeling the trajectory of the lower leg segment throughout a step for a given prosthetic foot and selecting design variables to minimize the error between this trajectory and target physiological lower leg kinematics. Thus far, previous work on the LLTE has mainly focused on optimizing conceptual foot architectures. To further study this metric, extensive clinical testing on prototypes optimized using this method has to be performed. Initial prototypes replicating the LLTE-optimal designs in previous work were optimized and built, but at 1.3 to 2.1 kg they proved too heavy and bulky to be considered for testing. A new, fully-characterized foot design reducing the weight of the final prototype while enabling ankle stiffness to be varied is presented and optimized for LLTE. The novel merits of this foot are that it can replicate a similar quasi-stiffness and range of motion of a physiological ankle, and be tested with variable ankle stiffnesses to test their effect on LLTE. The foot consists of a rotational ankle joint with interchangeable U-shaped constant stiffness springs ranging from 1.5 Nm/deg to 16 Nm/deg, a rigid structure extending 0.093 m from the ankle-knee axis, and a cantilever beam forefoot with a bending stiffness of 16 Nm2. The prototype was built using machined acetal resin for the rigid structure, custom nylon springs for the ankle, and a nylon beam forefoot. In preliminary testing, this design performed as predicted and its modularity allowed us to rapidly change the springs to vary the ankle stiffness of the foot. Qualitative feedback from preliminary testing showed that this design is ready to be used in larger-scale studies. In future work, extensive clinical studies with testing different ankle stiffnesses will be conducted to validate the optimization method using the LLTE as a design objective.

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Passive Prosthetic Foot Shape and Size Optimization Using Lower Leg Trajectory Error

Journal of Mechanical Design ◽

10.1115/1.4040779 ◽

2018 ◽

Vol 140 (10) ◽

Author(s):

Kathryn M. Olesnavage ◽

Victor Prost ◽

William Brett Johnson ◽

Amos G. Winter

Keyword(s):

Mechanical Design ◽

Three Dimensional ◽

Field Trials ◽

Lower Leg ◽

Element Analysis ◽

Trajectory Error ◽

Design Objective ◽

Prosthetic Foot ◽

Single Part ◽

Shape And Size

A method is presented to optimize the shape and size of a passive, energy-storing prosthetic foot using the lower leg trajectory error (LLTE) as the design objective. The LLTE is defined as the root-mean-square error between the lower leg trajectory calculated for a given prosthetic foot's deformed shape under typical ground reaction forces (GRFs), and a target physiological lower leg trajectory obtained from published gait data for able-bodied walking. Using the LLTE as a design objective creates a quantitative connection between the mechanical design of a prosthetic foot (stiffness and geometry) and its anticipated biomechanical performance. The authors' prior work has shown that feet with optimized, low LLTE values can accurately replicate physiological kinematics and kinetics. The size and shape of a single-part compliant prosthetic foot made out of nylon 6/6 were optimized for minimum LLTE using a wide Bezier curve to describe its geometry, with constraints to produce only shapes that could fit within a physiological foot's geometric envelope. Given its single part architecture, the foot could be cost effectively manufactured with injection molding, extrusion, or three-dimensional printing. Load testing of the foot showed that its maximum deflection was within 0.3 cm (9%) of finite element analysis (FEA) predictions, ensuring the constitutive behavior was accurately characterized. Prototypes were tested on six below-knee amputees in India—the target users for this technology—to obtain qualitative feedback, which was overall positive and confirmed the foot is ready for extended field trials.

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