Mechanical Adaptations In Walking Performance Using Ankle Foot Orthoses For Patients With Peripheral Artery Disease

Abstract

PURPOSE: Part of the limited success of community-based walking programs for people with peripheral artery disease (PAD) and intermittent claudication (IC) in the calf is a lack of strategies to manage pain during exercise. Carbon fiber ankle foot orthoses (AFO) could delay the onset of IC as they store elastic energy during stance that assists the calf muscles during gait propulsion. Clinical dogma may limit AFO implementation as many practitioners believe that AFO will reduce muscle recruitment during gait with a decline in function over time. Our purpose was to determine the gait adaptions in ankle mechanics, walking speed, and calf muscle recruitment when using AFOs to supplement a community walking program. METHODS: Fifteen patients with PAD (Age=67±12 yrs) were fitted with bilateral AFO. An initial 3D gait analysis with plantar flexor electromyography data was completed 1 week after fitting. We used a within-session comparison of walking with/without the AFO. Patients were then given standard advise to walk at home using the devices ad libitum for 12 weeks. Twelve patients completed follow up testing after 12 weeks. Differences between conditions and test times were analyzed using paired t-tests. RESULTS: The AFO reduced peak ankle plantar flexion power during the propulsion phase of walking at initial testing (mean±SE with AFO=1.5 ± 0.2 W · kg-1, without AFO=2.6 ± 0.3, p < 0.001). Reduced propulsion power was coupled with 4.5° less dorsiflexion during the terminal phase of stance (with AFO=8.6 ± 0.7°, without AFO=13.6 ± 0.9°, p < 0.001). Peak ankle plantar flexion moment and calf muscle recruitment did not change between conditions (p>0.05). The same pattern of results occurred at 12 weeks with no change in the variables over time (p>0.05). Gait speed was constant between conditions and over time (p>0.05; pooled initial=1.09 m · sec-1, pooled 12 weeks=1.06 m · sec-1). CONCLUSIONS: Maintenance of calf muscle recruitment when using the AFO was an unexpected, but favorable finding that contradicts conventional wisdom. Patients maintained normal values of ankle motion using AFO and sustained their gait velocity over time. The AFO reduces power demands on the calf muscle which has potential to reduce IC while still maintaining muscle integrity and walking function. Funding: Pilot and Mini-grants from NIH NIGMS 5U54GM104944.