Longitudinal kinematic and kinetic adaptations to obstacle crossing in recent lower limb amputees

A Review of Current State-of-the-Art Control Methods for Lower-Limb Powered Prostheses

Lower-limb prostheses aim to restore ambulatory function for individuals with lower-limb amputations. While the design of lower-limb prostheses is important, this paper focuses on the complementary challenge - the control of lower-limb prostheses. Specifically, we focus on powered prostheses, a subset of lower-limb prostheses, which utilize actuators to inject mechanical power into the walking gait of a human user. In this paper, we present a review of existing control strategies for lower-limb powered prostheses, including the control objectives, sensing capabilities, and control methodologies. We separate the various control methods into three main tiers of prosthesis control: high-level control for task and gait phase estimation, mid-level control for desired torque computation (both with and without the use of reference trajectories), and low-level control for enforcing the computed torque commands on the prosthesis. In particular, we focus on the high- and mid-level control approaches in this review. Additionally, we outline existing methods for customizing the prosthetic behavior for individual human users. Finally, we conclude with a discussion on future research directions for powered lower-limb prostheses based on the potential of current control methods and open problems in the field.

Toward Safe Wearer-Prosthesis Interaction: Evaluation of Gait Stability and Human Compensation Strategy Under Faults in Robotic Transfemoral Prostheses

Although advanced wearable robots can assist human wearers, their internal faults (i.e., sensors or control errors) also pose a challenge. To ensure safe wearer-robot interactions, how internal errors by the prosthesis limb affect the stability of the user-prosthesis system, and how users react and compensate for the instability elicited by internal errors are imperative. The goals of this study were to 1) systematically investigate the biomechanics of a wearer-robot system reacting to internal errors induced by a powered knee prosthesis (PKP), and 2) quantify the error tolerable bound that does not affect the user's gait stability. Eight non-disabled participants and two unilateral transfemoral amputees walked on a pathway wearing a PKP, as the controller randomly switched the control parameters to disturbance parameters to mimic the errors caused by locomotion mode misrecognition. The size of prosthesis control errors was systematically varied to determine the error tolerable bound that disrupted gait stability. The effect of the error was quantified based on the 1) mechanical change described by the angular impulse applied by the PKP, and 2) overall gait instability quantified using human perception, angular momentum, and compensatory stepping. The results showed that the error tolerable bound is dependent on the gait phase and the direction of torque change. Two balance recovery strategies were also observed to allow participants to successful respond to the induced errors. The outcomes of this study may assist the future design of an auto-tuning algorithm, volitionally-controlled powered prosthetic legs, and training of gait stability.

Validity of measures for life space mobility and physical activity in older adults with lower-limb amputation

BACKGROUND

Older adults with lower-limb amputations (LLAs) often experience lack of confidence and poor balance, which limits their mobility. There are few validated measures for assessing these outcomes in the LLA population.

OBJECTIVES

To assess the validity of the Life Space Assessment (LSA) and the Physical Activity Scale for the Elderly (PASE) for older adults with LLA.

STUDY DESIGN

Secondary analyses of cross-sectional data.

METHODS

Sixty-eight older adults with LLA across Canada were recruited to complete the LSA and the PASE. Validity was assessed via correlations with the Activities-specific Balance Confidence (ABC), Four-Square Step Test (FSST), and Two-Minute Walk Test (2-MWT).

RESULTS

As hypothesized, the LSA was positively correlated with the ABC (ρ = 0.36, 95% confidence interval [CI] [0.17, 0.62]) and 2-MWT (r = 0.49, 95% CI [0.27, 0.70]) and negatively correlated with FSST (ρ = -0.39, 95% CI [-0.56, -0.10]). The PASE was positively correlated with the ABC (ρ = 0.34, 95% CI [0.10, 0.56]) and 2-MWT (ρ = 0.32, 95% CI [0.05, 0.52]), and negatively correlated with FSST (ρ = -0.36, 95% CI [-0.53, -0.07]).

CONCLUSIONS

The LSA has validity in measuring life space mobility. The PASE captures the physical activity with weaker support of validity in older adults with LLA.

CLINICAL RELEVANCE

The LSA and PASE are quick low-cost tools for clinicians to assess mobility-related functional health and physical activity, respectively, in older adults with LLA. However, the PASE may contain activities that are not common among older adults with LLA.

Inter-limb weight transfer strategy during walking after unilateral transfemoral amputation

Although weight transfer is an important component of gait rehabilitation, the biomechanical strategy underlying the vertical ground reaction force loading/unloading in individuals with unilateral transfemoral amputation between intact and prosthetic limbs remains unclear. We investigated weight transfer between limbs at different walking speeds in 15 individuals with unilateral transfemoral amputation and 15 individuals without amputation as controls, who walked on an instrumented treadmill. The normalized unloading and loading rates were calculated as the slope of decay and rise phase of the vertical ground reaction force, respectively. We performed linear regression analyses for trailing limb's unloading rate and leading limb's loading rate between the prosthetic, intact, and control limbs. While loading rate increased with walking speed in all three limbs, the greatest increase was observed in the intact limb. In contrast to the other limbs, the prosthetic limb unloading rate was relatively insensitive to speed changes. Consequently, the regression line between trailing prosthetic and leading intact limbs deviated from other relationships. These results suggest that weight transfer is varied whether the leading or trailing limb is the prosthetic or intact side, and the loading rate of the leading limb is partially affected by the unloading rate of the contralateral trailing limb.

Longitudinal changes in transtibial amputee gait characteristics when negotiating a change in surface height during continuous gait

BACKGROUND

Negotiating a raised surface during continuous gait is an important activity of daily living and is a potentially hazardous task with regards to trips, falls and fall-related injury. However, it is not known how recent transtibial amputees adapt to performing stepping gait tasks in the 6-month period following discharge from rehabilitation.

METHODS

Recent transtibial amputees performed continuous gait trials, stepping onto and from a raised surface walkway representing the height of a street kerb, whilst kinematic and kinetic data were recorded at one, three and six months post-discharge from rehabilitation.

FINDINGS

Walking speed increased when stepping down (p=0.04) and was invariant across the study period when stepping up. At one month post-discharge, participants displayed an affected lead limb preference (90.8%) when stepping down and an intact lead limb preference (70.0%) when stepping up, although these lead limb preferences diminished over time. Participants spent more time in stance on the intact limb compared to the affected limb in both stepping down (trail limb) (p=0.01) and stepping up (lead and trail limbs) (p=0.05). Participants displayed significantly greater joint mobility and power bursts in the intact trail limb when stepping down and in the intact lead limb when stepping up.

INTERPRETATION

Transtibial amputees prefer to exploit intact limb function to a greater extent, although over time, the means by which this occurs changes which affects the initial lead limb preferences. The results from the current study enable future evidence-based therapeutic and prosthetic interventions to be designed that improve transtibial amputee stepping gait.