Custom Passive Dynamic Ankle-Foot Orthoses Can Improve Walking Economy and Speed Post-Stroke

Background Introduction

Stroke is one of the leading causes of long-term disability, affecting over 795,000 individuals annually in the United States. A common post-stroke issue is plantar flexor weakness in the affected limb, impacting the ability to control forward limb rotation during mid-stance to terminal stance phases and forward propulsion during the push-off phase. Impaired plantar flexor function can lead to excessive ankle dorsiflexion during mid-stance or persistent knee hyperextension, which subsequently causes reduced gait speed, asymmetric stride length, and increased walking metabolic cost. These issues diminish stroke survivors’ mobility and participation in daily activities, further affecting their physical and mental health.

Passive-dynamic ankle–foot orthoses (PD-AFOs), with their spring-like bending stiffness, provide resistance during ankle dorsiflexion and store mechanical energy, releasing this energy during the push-off phase to simulate the function of healthy plantar flexors. However, despite some studies indicating positive effects of PD-AFOs on gait and metabolic costs, the lack of standardized objective prescription guidelines makes it difficult to customize PD-AFOs for individual needs.

Paper Source

This paper is written by Jacob T. Skigen and his team, involving researchers from the University of Delaware, the University of Iowa, and other institutions. It was published in the Journal of NeuroEngineering and Rehabilitation (2024, Vol. 21, No. 126). The paper is open access and co-authored by multiple researchers.

Research Process

Study Subjects and Experimental Design

Researchers selected 32 eligible long-term hemiplegic post-stroke patients. These patients had previously been prescribed AFOs by doctors and exhibited plantar flexor weakness in the affected limb. All participants attended three laboratory visits, each testing conditions including no AFO, a standard care (SOC) AFO, and a customized PD-AFO.

Visit 1: Initial Assessment and Data Collection

During the first visit, the research team used instrumented gait analysis and a 10-meter walk test to record participants’ self-selected walking speed (SSWS). Additionally, the geometric data of each participant’s non-affected limb were recorded to provide baseline data for customizing the PD-AFO.

PD-AFO Customization Process

Using Visual 3D software, the peak net plantar flexion moment of each participant was calculated and determined to customize the PD-AFO. Carbon fiber pre-impregnated materials were used to fabricate the PD-AFO, ensuring that the bending stiffness of each prosthesis precisely matched the patient’s needs.

Visit 2: SOC-AFO Testing

During the second visit, participants wore the SOC-AFO for laboratory gait analysis and retook the 10-meter walk test while completing the Orthotics and Prosthetics Users’ Survey (OPUS) and the Quebec User Evaluation of Satisfaction with Assistive Technology (QUEST) questionnaire.

Visit 3: Custom PD-AFO Testing

Participants wore their customized PD-AFO and were allowed sufficient time to adapt to walking with it. After adaptation, they underwent laboratory gait analysis and the 10-meter walk test again, and completed the OPUS and QUEST questionnaires to evaluate their satisfaction with the customized PD-AFO.

Data Analysis

Various statistical analysis methods were used to compare participants’ gait performance under different conditions. Repeated measures ANOVA or Friedman tests were conducted for group analysis, and simulation modeling analysis (SMA) was used for individual-level analysis. Key analysis variables included the cost of transport (COT), SSWS, peak ankle dorsiflexion, and plantar flexion moments.

Research Results

Group-Level Results

In both the experimental and control groups, wearing the customized PD-AFO significantly reduced mechanical COT and increased SSWS. Specific data are as follows: 1. Significant reduction in COT: The COT for the no-AFO and SOC-AFO groups were 2.64 and 2.51 J/kg/m, respectively, while the PD-AFO group was 2.28 J/kg/m. 2. Significant increase in SSWS: The SSWS for the no-AFO and SOC-AFO groups were 0.62 and 0.64 m/s, respectively, while the PD-AFO group was 0.73 m/s. 3. Satisfaction evaluation: The OPUS and QUEST questionnaire scores for the PD-AFO group were significantly higher than those for the SOC-AFO group.

Individual-Level Results

Individual-level analysis showed significant variation in responses among different participants. Some participants significantly reduced their COT after wearing the PD-AFO, while others did not show significant changes. Additionally, gait biomechanical parameters did not show consistent improvements. This indicates that due to the heterogeneity of post-stroke gait, different participants might adopt different gait adaptation strategies, thereby affecting the results.

Conclusion and Significance

This study is the first to verify that customized PD-AFOs can effectively reduce mechanical COT and increase walking speed based on the degree of individual plantar flexor weakness. Although consistent improvements in gait biomechanical parameters were not achieved, the overall functional and satisfaction improvements with customized PD-AFOs still hold significant clinical value. Future research should explore the specific applicable populations and optimal customization methods for PD-AFOs to further optimize post-stroke rehabilitation treatment.

This study provides preliminary evidence for developing objective prescription guidelines for PD-AFOs and lays the foundation for future clinical applications. Next steps in research should focus on identifying patient characteristics suitable for PD-AFOs, uncovering the mechanisms behind COT and SSWS reduction, and further validating the effects after a longer adaptation period.