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Exploratory Assessment of Robotic Ankle Foot Orthosis Stiffness and Neutral Angle on Stair Ambulation in Individuals
Samuel Hopkins1, Connor Gaudette2, Maria Jose Silvetti2
1Department of Mechanical Engineering, Northern Arizona University, Sanghi College of Engineering, Flagstaff, AZ, USA. ssh252@nau.edu.
Purpose:
Individuals who wear Ankle Foot Orthoses (AFOs) express a desire for adaptability and improved stair ambulation. This exploratory study examined how the stiffness and neutral angle of a robotic AFO influence stair ambulation and preference in spastic cerebral palsy (CP) and compared robotic AFOs, solid AFOs, and shoes alone.
Methods:
Seven individuals with spastic CP completed modified Timed-Up-and-Down-Stairs (TUDS) tests under nine robotic AFO stiffness-neutral angle configurations, solid AFOs, and shoes alone. Outcomes included TUDS time, ankle kinematics, soleus and vastus lateralis activity, exertion, balance confidence, trunk instability, stiffness preference, and device power and torque. Mixed effects modeling assessed the effects of stiffness and neutral angle. Stiffness preference was evaluated during level walking, stair ascent, and descent. Repeated measures ANOVA compared robotic AFOs, solid AFOs, and shoes alone.
Results:
Increased stiffness and more plantarflexed neutral angles decreased peak dorsiflexion (p < 0.05) and increased peak torque (p < 0.05). Few other outcomes were affected. Four of seven participants preferred low stiffness across all tasks. Robotic AFOs performed better than solid AFOs, by decreasing TUDs time (- 27%, d = - 0.66, p < 0.05) and increasing confidence (49%, d = 0.92, p < 0.05) in descent, but not better than shoes alone. During stair ascent, the only difference between the AFOs and shoes was a reduction in soleus activity between solid AFOs and shoes alone.
Conclusion:
Robotic AFO configuration influences stair descent and may improve descent speed and confidence over solid AFOs in a limited sample of spastic CP.
