Differential and Adjustable Stiffness Leaf Spring Ankle Foot Orthoses Enhance Gait Propulsion and Task Versatility in Cerebral Palsy

Abstract

Purpose

This study explored the effectiveness of a novel differential and adjustable stiffness leaf spring AFO (DAS-AFO) during standing, walking, and sit-to-stand tasks among individuals with cerebral palsy.

Methods

Eleven individuals with cerebral palsy, ages 12–41, completed treadmill walking trials with the DAS-AFO, a solid (i.e., rigid) AFO, and without an assistive device (shod). We quantified metabolic cost, muscle activity of the soleus and vastus lateralis, and lower body kinetics and kinematics. Participants also performed overground walking, sit-to-stand, and stable standing tasks while wearing the DAS-AFO and reported their preferred stiffness setting for each task. Additionally, we quantified center of pressure during the stable standing task.

Results

Walking with the DAS-AFO resulted in an average 24% increase in ankle push-off power when compared to the solid AFO (p = .003). Both AFO conditions resulted in an average 16% reduction in soleus activity compared to shod (p < .040); only the DAS-AFO reduced vastus lateralis activity compared to shod (13% average reduction, p = .015). Over half of the participants preferred a different AFO stiffness for at least one of the tasks of daily living. No stiffness setting was universally preferred for a single task. During the stable standing task, the high stiffness setting increased average anterior–posterior center of pressure excursion (p = .022) and velocity (p = .001) compared to shod.

Conclusion

Our findings highlight potential benefits of the DAS-AFO design over solid AFOs, including improved ankle joint motions and push-off power during walking. Customizability of the DAS-AFO positively influenced participant preference and task performance.