The Effect of Backward Perturbation on Fall Outcomes in Ankle Foot Orthosis (AFO) and Functional Electrical Stimulator (FES) Users with Chronic Stroke

Between 20%-30% of stroke survivors have foot drop. Foot drop is characterized by inadequate dorsiflexion required to clear the foot of the ground during the swing phase of gait, increasing the risk of stumbles and falls (Pouwels et al. 2009; Hartholt et al. 2011). External postural perturbations such as trips and slips are associated with high rate of falls in individuals with stroke (Forster et al. 1995). Falls often results in head, hip, and wrist injuries (Hedlund et al 1987; Parkkari et al. 1999). A critical response necessary to recover one’s balance and prevent a fall is the ability to evoke a compensatory step (Maki et al. 2003; Mansfield et al. 2013). This is the step taken to restore one’s balance and prevent a fall. However, this is difficult for stroke survivors with foot drop as normal gait is impaired and this translates to difficulty in evoking a compensatory step. To address both foot drop and poor compensatory stepping response, assistive devices such as the ankle-foot-orthosis (AFO) and functional electrical stimulator (FES) are generally prescribed to stroke survivors (Kluding et al. 2013; S. Whiteside et al. 2015). The use of these assistive devices improves walking speed, foot clearance, cadence, and step length of its users (Bethoux et al. 2014; Abe et al. 2009; Everaert et al. 2013; Alam et al. 2014). However, their impact on fall outcome in individuals with stroke in not well evaluated (Weerdesteyn et al. 2008). A recent study (Masood Nevisipour et al. 2019) where stroke survivors experienced a forward treadmill perturbation, mimicking a trip, reports that the impaired compensatory stepping response in stroke survivors in not due to the use of the assistive devices but to severe ankle impairments which these devices do not fully address. However, falls can also occur because of a slip. Slips constitute 40% of outdoor falls (Luukinen et al. 2000). In this study, results for fall rate and compensatory stepping response when subjects experience backward perturbations, mimicking slips, reveal that these devices do not impair the compensatory stepping response of its users.