Stiffness of the arizona ankle-foot orthosis before and after modification for gait analysis

The purpose of this project was to measure the stiffness of the Arizona ankle-foot orthosis (AFO) before and after it was modified for gait analysis with a foot specific marker set. Five Arizona AFOs were tested in the intact condition in a custom testing device in the sagittal and coronal planes. After testing in the intact condition, 2.5-cm diameter holes were drilled in the malleoli and the medial, lateral, and posterior aspects of the calcaneus. Three cycles of loading in each plane were averaged for analysis. The slope of the load-displacement curve was calculated to determine the brace stiffness. The coefficient of repeatability was 0.17 Nm per degree in plantarflexion, 0.16 Nm per degree in dorsiflexion, 0.38 Nm per degree in inversion, and 0.18 Nm per degree in eversion. The stiffness decreased significantly in plantarflexion and dorsiflexion but not in the coronal plane motions. The change in stiffness in plantarflexion increased with an increase in the height of the medial malleolus holes. This relationship was significant, as determined by the Hotellings t test (p 0.04), which suggests that the Arizona AFO should be reinforced on the medial side before it can be used in gait analysis studies. (J Prosthet Orthot. 2009;21:204‐207.) KEY INDEXING TERMS: Arizona AFO, stiffness, biomechanics, gait analysis