The Effect of Moderate Parkinson's Disease on the Biomechanics of Compensatory Backwards Stepping

Abstract

Postural instability leading to falls is one of the major unmet needs in the treatment of Parkinson's disease (PD). The progression of postural instability is not well understood, and a better understanding of the biomechanics underlying the progression of postural instability may be instrumental in the development of more sensitive clinical measures of postural instability and fall risk in PD. The biomechanical analysis of the response to a balance perturbation provides an opportunity to better understand postural instability in PD. This study examined the compensatory stepping response to a backwards pull in participants with moderate PD compared to age-range matched healthy controls. The first study investigated the overall response to a balance disturbance in moderate PD, and found that patients with moderate PD utilized more steps to regain balance, had a longer weight shift time, and used a base-width neutral step as a strategy to regain balance, compared to controls. The second study further investigated the compensatory response by focusing on the preparation phase and found that participants with moderate PD used multiple anticipatory postural adjustments (APAs), resulting in longer liftoff times and significantly different movement in the center of pressure prior to liftoff compared to healthy controls. The third study investigated the effects of PD and step strategy (single step, multiple steps, and a base-width neutral step) on balance recovery and found that participants with moderate PD took significantly longer to recover balance, and that the type of strategy used to respond to the disturbance significantly impacted recovery time. Additionally, the use of a base-width neutral step as the first step in the response emerged as a strategy that has not been previously documented and significantly delays balance recovery. These results suggest that moderate PD significantly impairs the compensatory response to a backwards pull. Furthermore, this impairment could be attributed to a delay in the preparation phase of the step response. This delay was associated with the use of multiple anticipatory postural adjustments and/or the use of a base-width neutral step as the first step in the response. Further study should examine the progression of impairment in these compensatory responses across PD severity levels, and the correlation with fall risk.