Researchers, noting that an AFO’s sagittal plane rotational stiffness can affect gait kinematics, evaluated the influence of rotational speed on AFO’s stiffness properties near the ankle.
For the study, the researchers tested a sample of one thermoplastic off-the-shelf AFO and two 3D-printed carbon fiber enforced nylon AFOs. Each AFO’s dynamic resistance torque was measured as it was flexed at five speeds using a custom-built measurement apparatus. They compared loading stiffness, neutral angle, and energy dissipation parameters for each AFO across speeds.
The data indicated that parameter values were generally greater at higher speeds, and the effects were statistically significant for all AFOs. However, differences in AFO stiffness and neutral angle across speeds were quite small (< 0.6 Nm/° and < 2.2°). Changes in the thermoplastic AFO's stiffness was lower than the minimum detectable difference. Energy dissipation, as indicated by hysteresis area, increased by up to 6.3 J (about 250 percent) at the highest speed.
This demonstrates that AFO flexion speed can influence the properties of different AFOs over the range typically achieved in human walking, according to the study. Future work should assess whether the observed small variations of stiffness and neutral angle have a clinically meaningful impact on user performance, as well as explore effects of angular speed on a variety of AFO materials and designs, the authors concluded.
The study, “The effect of rotational speed on ankle-foot orthosis properties,” was published in the Journal of Biomechanics.
