Comparison of five different methodologies for evaluating ankle-foot orthosis stiffness

Area of Science:

• Biomechanics
• Orthotics and Prosthetics Engineering

Background:

• Ankle-foot orthosis (AFO) mechanical properties significantly influence user gait mechanics.
• Current methodologies for evaluating AFO mechanical properties lack standardization.

Purpose of the Study:

• To compare the outcomes of five distinct evaluation frameworks for assessing AFO stiffness.
• To highlight the impact of non-standardized testing on AFO mechanical property measurements.

Main Methods:

• Five different testing methods were employed to evaluate 13 carbon composite AFOs.
• Four methods used custom test fixtures for dorsiflexion in the sagittal plane; one involved quasi-static deflection via hanging weights.
• Rotational stiffness was calculated, and differences between methods were statistically analyzed.

Main Results:

• Significant differences in measured AFO stiffness were observed across the five methods.
• Methods with less constrained motion (e.g., hanging weights) yielded lower stiffness values.
• The relative difference in stiffness measurements between methods ranged from 13% to 156%.

Conclusions:

• The study underscores the critical need for standardized mechanical testing protocols for AFOs.
• Methodological variations lead to substantial discrepancies in stiffness measurements, potentially limiting clinical application.
• Standardization is essential for reliable AFO stiffness metrics in clinical prescription and research.