The influence of orthosis options on walking parameters in spinal cord-injured patients: a literature review

Design of a Quasi-Passive Ankle-Foot Orthosis with Customizable, Variable Stiffness

Most commercial ankle-foot orthoses (AFOs) are passive structures that cannot modulate stiffness to assist with a diverse range of activities, such as stairs and ramps. It is sometimes possible to change the stiffness of passive AFOs through reassembly or benchtop adjustment, but they cannot change stiffness during use. Passive AFOs are also limited in their ankle mechanics and cannot replicate a biomimetic, nonlinear torque-angle relationship. Many research labs have developed ankle exoskeletons that show promise as viable alternatives to passive AFOs, but they face challenges with reliability, mass, and cost. Consequently, commercial translation has largely failed to date. Here we introduce the Variable Stiffness Orthosis (VSO), a quasi-passive variable stiffness ankle-foot orthosis that strikes a balance between powered and passive systems, in terms of mass, complexity, and onboard intelligence. The VSO has customizable torque-angle relationships via a cam transmission, and can make step-to-step stiffness adjustments via motorized reconfiguration of a spring support along a lead-screw. In this work, we introduce two versions: a nominal and a stiff prototype, which differ primarily in their mass and available stiffness levels. The available torque-angle relationships are measured on a custom dynamometer and closely match model predictions. The experimental results showed that the prototypes are capable of producing ankle stiffness coefficients between 9 - 330 Nm/rad.

Systematic Reviews of Clinical Benefits of Exoskeleton Use for Gait and Mobility in Neurologic Disorders: A Tertiary Study

OBJECTIVE

To describe systematic reviews (SRs) of the use of exoskeletons for gait and mobility by persons with neurologic disorders and to evaluate their quality as guidance for research and clinical practice.

DATA SOURCES

PubMed, EMBASE, Web of Science, CINAHL Complete, PsycINFO, Cochrane Database of Systematic Reviews, PEDro, and Google Scholar were searched from database inception to January 23, 2018.

STUDY SELECTION

A total of 331 deduplicated abstracts from bibliographic database and ancestor searching were independently screened by 2 reviewers, resulting in 109 articles for which full text was obtained. Independent screening of those 109 articles by 2 reviewers resulted in a final selection of 17 SRs.

DATA EXTRACTION

Data were extracted by 1 reviewer using a pretested Excel form with 158 fields and checked by a second reviewer. Key data included the purpose of the SR, methods used, outcome measures presented, and conclusions. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses and A MeaSurement Tool to Assess Systematic Reviews version 2 were used to evaluate reporting and methodological quality, respectively, of the SRs.

DATA SYNTHESIS

The SRs generally were of poor methodological and reporting quality. They failed to report some information on patients (eg, height, weight, baseline ambulatory status) and interventions (eg, treatment hours or sessions planned and delivered) that clinicians and other stakeholders might want to have, and often failed to notice that the primary studies duplicated subjects.

CONCLUSIONS

Published SRs on exoskeletons have many weaknesses in design and execution; clinicians, researchers, and other stakeholders should be cautious in relying on them to make decisions on the use of this technology. Future primary and secondary studies need to address the multiple methodological limitations.

The impact of ankle-foot orthosis stiffness on gait: A systematic literature review

BACKGROUND

Ankle-foot orthoses (AFOs) are commonly prescribed to provide ankle support during walking. Current prescription standards provide general guidelines for choosing between AFO types, but are limited in terms of guiding specific design parameter choices. These design parameters affect the ankle stiffness of the AFO.

RESEARCH QUESTION

The aim of this review was to investigate the impact of AFO stiffness on walking mechanics.

METHODS

A literature search was conducted using three databases: Pubmed, Engineering Village, and Web of Science.

RESULTS

After applying the exclusion criteria, 25 of 287 potential articles were included. The included papers tested a range of stiffnesses (0.02-8.17 Nm/deg), a variety of populations (e.g. healthy, post-stroke, cerebral palsy) and various gait outcome measures. Ankle kinematics were the most frequently reported measures and the most consistently affected by stiffness variations. Greater stiffnesses generally resulted in reduced peak ankle plantarflexion, dorsiflexion, and total range of motion, as well as increased dorsiflexion at initial contact. At the knee, a few studies reported increased flexion at initial contact, and decreased peak extension and increased peak flexion during stance when stiffness was increased. Stiffness did not affect hip kinetics and there was low evidence for its effects on hip or pelvis kinematics, ankle and knee kinetics, muscle activity, metabolic cost, ground reaction forces and spatiotemporal parameters. There were no generalizable trends for the impact of stiffness on user preference.

SIGNIFICANCE

AFO stiffness is a key factor influencing ankle movement. Clear reporting standards for AFO design parameters, as well as additional high quality research is needed with larger sample sizes and different clinical populations to ascertain the true effect of stiffness on gait.