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 P osterior tibial tendon dysfunction (PTTD) is the most common cause of adult acquired flatfoot deformity. The majority of articles on PTTD focus on describing methods for operative treatment of this disorder. There are few studies quantifying the effects of nonoperative treatment. Nonoperative treatments for PTTD include ready-made orthotics and braces or custom-made orthotics, including the Arizona ankle-foot orthosis (AFO), articulated AFOs, and the University of California Biomechanics Laboratory (UCBL) orthosis. The effects of the Arizona AFO were evaluated in patients with PTTD using three clinical measures, the American Orthopaedic Foot and Ankle Society hindfoot score, the Foot Function index, and the SF-36. Significant improvements were seen in all three indices after treatment. Additionally, patients who were dependent on pain medication decreased or eliminated the use of medication for pain. Alvarez et al. evaluated the use of shortarticulated AFO with an instep wrap and full-length toe plate and a three-quarter length thermoplastic elastomer foot orthosis with high medial and lateral trim lines in combination with an aggressive therapy program in 47 patients. After treatment, foot and ankle pain decreased significantly, 83% of patients could perform a single heel rise with no pain, and there was a significant increase in eccentric and concentric ankle strength. The effects of nonoperative treatment have been quantified in vitro by examining changes in midfoot and hindfoot kinematics and plantar pressures before and after creating a flatfoot deformity. The Arizona AFO, the UCBL, a molded AFO, and various off-the-shelf ankle braces were tested. The off-the-shelf braces had little effect on the restoration of kinematics, the UCBL orthosis partially restored kinematics at the arch and hindfoot and the Arizona AFO restored midfoot height. Although this study provided insight into the effects of different nonoperative treatment on the hindfoot and midfoot kinematics, the tests were completed with static loading during one portion of the gait cycle. To properly evaluate the effects of nonoperative treatment on PTTD, it is necessary to perform a quantitative gait analysis in vivo. Holes must be placed in the orthotic to measure ankle kinematics, using a lower limb marker set, such as the Helen Hayes marker set. These modifications may include holes over the malleoli and calcaneus. Therefore, braces, such as the Arizona AFO (Arizona AFO, Inc., Mesa, AZ), must be modified to allow for placement of the markers. The purpose of this study was 1) to determine the stiffness of the Arizona AFO in the sagittal and coronal planes before and after it is modified for gait analysis and 2) to determine whether the brace should be modified to function as designed.