Modulation of anticipatory postural adjustments using a powered ankle orthosis in people with Parkinson's disease and freezing of gait

Background: Freezing of gait (FOG) during gait initiation in people with Parkinson's disease (PD) may be related to a diminished ability to generate anticipatory postural adjustments (APAs). Externally applied perturbations that mimic the desired motion of the body during an APA have been demonstrated to shorten and amplify APAs; however, no portable device has been tested. In this study, a portable powered ankle-foot orthosis (PPAFO) testbed was utilized to investigate the effect of mechanical assistance, provided at the ankle joint, on the APAs during gait initiation. Research question: Does mechanical assistance provided at the ankle joint improve APAs during gait initiation in people with PD and FOG? Methods: Thirteen participants with PD and FOG initiated gait across five test conditions: two self-initiated (uncued) conditions in walking shoes [Baseline-Shoes], and the PPAFO in unpowered passive mode [Baseline-PPAFO(passive)]; three go cued conditions that included an acoustic tone with the PPAFO in unpowered passive mode [Acoustic + PPAFO(passive)], the mechanical assistance from the PPAFO [PPAFO(Acti)(ve)], and the acoustic tone paired with mechanical assistance [Acoustic + PPAFO (Acti)(ve)]. A warning-cue preceded the imperative go cue for all the cued trials. Peak amplitudes and timings of the vertical ground reaction forces (GRFs) and center of pressure (COP) shifts from onset to toe-off were compared across conditions. Results: Mechanical assistance significantly increased the peak amplitudes of the GRFs and COP shifts, reduced APA variability, and decreased the time to toe-off relative to the passive conditions. Significance: These findings demonstrate the potential utility of mechanical assistance at the ankle joint (with or without an acoustic cue) as a method to generate more consistent, shortened, and amplified APAs in people with PD and FOG.