The impact of ankle-foot-orthosis (AFO) use on the compensatory stepping response required to avoid a fall during trip-like perturbations in young adults: Implications for AFO prescription and design

Ankle-foot-orthoses (AFOs) are commonly prescribed to treat foot drop and enhance walking in fall-prone individuals (e.g. stroke). AFOs improve static balance but AFO-users are still at high fall risk. To our knowledge, no one has studied the biomechanical effect of AFO-use on the compensatory stepping response required to avoid falling during dynamic conditions such as trip, the leading cause of falls. The objective of this study is to evaluate the impact of a semi-rigid thermoplastic AFO on the compensatory stepping response in young healthy individuals following trip-like treadmill perturbations. We found that the AFO on the stepping leg (AFO-step) decreased trunk stability (increased trunk angle and angular velocity), shortened the compensatory step length, and reduced dynamic stability (smaller COM-BOS). AFO on the support leg (AFO-support) was only marginally different from the No-AFO condition. Detrimental changes in compensatory stepping response (e.g. decreased trunk stability) were linearly correlated to diminished propulsive impulse of the step. In summary, AFO-use on the stepping leg is associated with impaired compensatory stepping response (e.g. reduced trunk stability) and decreased propulsive impulse in young adults. It is important to note that AFO-use enhances static stability and decreases the probability of a trip/stumble occurring indicating they are important for fall prevention. Still, our results suggest that AFO-use may impair the compensatory stepping response after a trip/stumble has occurred and may suggest that preserving plantarflexion function may support the compensatory stepping response. Further study of these devices and their impact on compensatory stepping response in fall-prone individuals is warranted.