A more compliant prosthetic foot better accommodates added load while walking among Servicemembers with transtibial limb loss

A Review of Natural Fiber-Reinforced Composites for Lower-Limb Prosthetic Designs

This paper presents a comprehensive review of natural fiber-reinforced composites (NFRCs) for lower-limb prosthetic designs. It covers the characteristics, types, and properties of natural fiber-reinforced composites as well as their advantages and drawbacks in prosthetic designs. This review also discusses successful prosthetic designs that incorporate NFRCs and the factors that make them effective. Additionally, this study explores the use of computational biomechanical models to evaluate the effectiveness of prosthetic devices and the key factors that are considered. Overall, this document provides a valuable resource for anyone interested in using NFRCs for lower-limb prosthetic designs.

A Passive Three Degree of Freedom Transtibial Prosthesis With Adjustable Coronal Compliance and Independent Toe Joint

The effects of including lateral compliance or a toe joint in transtibial prostheses have been studied independently, showing the potential to improve the gait biomechanics in terms of stability, walking speed, and metabolic cost. However, both of these features are not commonly found in commercial prostheses despite their importance in human gait. In this work, we present a multi-axis passive transtibial prosthesis with three degrees of freedom (DOF). The prosthesis includes a compliant and adjustable coronal articulation using beam springs, an independent 3D-printed flexible forefoot as a toe joint, and sagittal dorsiflexion-plantarflexion stiffness using a helicoidal spring. We mechanically characterize each degree of freedom in terms of the provided stiffness. The measured stiffness values were 3.26Nm/deg, 4.94, or 5.63 Nm/deg in the sagittal plane (with different springs), and 2.54 Nm/deg, 2.79 Nm/deg, 2.94 Nm/deg, or 3.72 Nm/deg in the coronal plane (by adjusting the mechanism). Finally, the effect of different types of infill and infill levels for the 3D printed toes were explored, showing stiffness varying from 2.05 N/mm to 350 N/mm. The obtained sagittal stiffness is beneath the ones found in able-bodied persons; in contrast, the lateral stiffness values are comparatively higher than that of the able-bodied persons. However, the current design is simple to rearrange and modify the stiffness values. Lastly, the wide range of stiffness achievable in the 3D printed toes can be useful to achieve proper torque requirements in the forefoot for a broad range of users.

Biomechanical characterization of the foot-ground interaction among Service members with unilateral transtibial limb loss performing unconstrained drop-landings: Effects of drop height and added mass

There exist limited data to guide the development of methodologies for evaluating impact resilience of prosthetic ankle-foot systems, particularly regarding human-device interaction in ecologically valid scenarios. The purpose of this study was to biomechanically characterize foot-ground interactions during drop-landings among Service members with and without unilateral transtibial limb loss. Seven males with, and seven males without, unilateral transtibial limb loss completed six drop-landing conditions consisting of all combinations of three heights (20 cm, 40 cm, 60 cm) and two loads (with and without a 22.2 kg weighted vest). Peak ground reaction forces (GRF), vertical GRF loading rate and impulse, as well as ankle-foot, knee, and hip joint negative (absorption) powers and work were compared across groups (i.e., contralateral side and prosthetic side vs. uninjured controls) by height and load conditions. Loading occurred primarily in the vertical direction, and increased with increasing drop height and/or with added load. Vertical GRFs were overall ~ 15% smaller on the prosthetic side (vs. controls) with similar loading rates across limbs/groups. From the most challenging condition (i.e., 60 cm with 22 kg load), ankle-foot absorption energies on the prosthetic side were 64.6 (7.2) J; corresponding values were 187.4 (8.9) J for the contralateral limb and 161.2 (6.7) J among uninjured controls. Better understanding biomechanical responses to drop-landings in ecological scenarios will help inform future iterations of mechanical testing methodologies for evaluating impact resilience of prosthetic ankle-foot systems (enhancing prescription criteria and return-to-activity considerations) as well as identifying and mitigating risk factors for long-term secondary complications within the contralateral limb (e.g., joint degeneration).

Reducing stiffness of shock-absorbing pylon amplifies prosthesis energy loss and redistributes joint mechanical work during walking

BACKGROUND

A shock-absorbing pylon (SAP) is a modular prosthetic component designed to attenuate impact forces, which unlike traditional pylons that are rigid, can compress to absorb, return, or dissipate energy. Previous studies found that walking with a SAP improved lower-limb prosthesis users' comfort and residual limb pain. While longitudinal stiffness of a SAP has been shown to affect gait kinematics, kinetics, and work done by the entire lower limb, the energetic contributions from the prosthesis and the intact joints have not been examined. The purpose of this study was to determine the effects of SAP stiffness and walking speed on the mechanical work contributions of the prosthesis (i.e., all components distal to socket), knee, and hip in individuals with a transtibial amputation.

METHODS

Twelve participants with unilateral transtibial amputation walked overground at their customary (1.22 ± 0.18 ms^-1) and fast speeds (1.53 ± 0.29 ms^-1) under four different levels of SAP stiffness. Power and mechanical work profiles of the leg joints and components distal to the socket were quantified. The effects of SAP stiffness and walking speed on positive and negative work were analyzed using two-factor (stiffness and speed) repeated-measure ANOVAs (α = 0.05).

RESULTS

Faster walking significantly increased mechanical work from the SAP-integrated prosthesis (p < 0.001). Reducing SAP stiffness increased the magnitude of prosthesis negative work (energy absorption) during early stance (p = 0.045) by as much as 0.027 Jkg^-1, without affecting the positive work (energy return) during late stance (p = 0.159), suggesting a damping effect. This energy loss was partially offset by an increase in residual hip positive work (as much as 0.012 Jkg^-1) during late stance (p = 0.045). Reducing SAP stiffness also reduced the magnitude of negative work on the contralateral sound limb during early stance by 11-17% (p = 0.001).

CONCLUSIONS

Reducing SAP stiffness and faster walking amplified the prostheses damping effect, which redistributed the mechanical work, both in magnitude and timing, within the residual joints and sound limb. With its capacity to absorb and dissipate energy, future studies are warranted to determine whether SAPs can provide additional user benefit for locomotor tasks that require greater attenuation of impact forces (e.g., load carriage) or energy dissipation (e.g., downhill walking).

Speed Adaptable Prosthetic Foot: Concept Description, Prototyping and Initial User Testing

This article presents a novel design of a prosthetic foot that features adaptable stiffness that changes according to the speed of ankle motion. The motivation is the natural graduation in stiffness of a biological ankle over a range of ambulation tasks. The device stiffness depends on rate of movement, ranging from a dissipating support at very slow walking speed, to efficient energy storage and return at normal walking speed. The objective here is to design a prosthetic foot that provides a compliant support for slow ambulation, without sacrificing the spring-like energy return beneficial in normal walking. The design is a modification of a commercially available foot and employs material properties to provide a change in stiffness. The velocity dependent properties of a non-Newtonian working fluid provide the rate adaptability. Material properties of components allow for a geometry shift that results in a coupling action, affecting the stiffness of the overall system. The function of an adaptive coupling was tested in linear motion. A prototype prosthetic foot was built, and the speed dependent stiffness measured mechanically. Furthermore, the prototype was tested by a user and body kinematics measured in gait analysis for varying walking speed, comparing the prototype to the original foot model (non-modified). Mechanical evaluation of stiffness shows increase in stiffness of about 60% over the test range and 10% increase between slow and normal walking speed in user testing.