Obstacle crossing in Parkinson's disease: Mediolateral sway of the centre of mass during level-ground walking and obstacle crossing

Highlights

• Some people with PD sway sideways abnormally far and fast when walking.

• Obstacle crossing can exacerbate abnormal sideways sway in people with PD.

• People with more severe PD sway faster when crossing obstacles.

Abstract

Background

Falls are common in idiopathic Parkinson's disease (PD) and frequently occur when walking and crossing obstacles.

Objective

To determine whether people with mild to moderately severe PD have abnormal centre of mass (CoM) motion in response to the perturbations of level-ground walking and obstacle crossing.

Method

Mediolateral excursion and velocity of the CoM were measured using three-dimensional motion analysis and force platforms in 20 people with mild to moderately severe PD at the peak dose of their PD medication, and 20 age and sex matched healthy control participants.

Results

People with PD had greater sideways sway than healthy older adults when walking, particularly when walking over obstacles. People with PD also maintained their CoM more medial to their stance foot throughout the swing phase of gait compared to controls. The severity of motor symptoms in people with PD, measured using the UPDRS-III, was associated with faster sideways CoM motion but not increased CoM excursions.

Conclusions

Environmental hazards, such as ground-based obstacles, may accentuate postural instability in people with PD. Increased mediolateral sway might be due to impaired postural responses or kinematic compensations to increase foot clearance. Fall prevention programs could benefit from inclusion of components educating people with PD about the risks associated with obstacle crossing when walking.

Introduction

Postural instability during level-ground walking and obstacle crossing is common and disabling in people with PD. As well as predisposing people with PD to tripping, it can also be associated with a fear of falling and loss of confidence in walking [1], [2]. Falls occur in up to 60% of people with PD [3] and sideways falls are a leading cause of lateral hip fractures in older adults [4]. Sideways falls are also associated with high mortality rates [5]. Investigating mediolateral balance in people with PD is important because evidence from posturography studies indicates that people with moderate-severe PD do not control their balance as well as healthy older adults [6], [7], [8], [9].

Several gait studies have shown that people with PD have postural instability during walking and in particular during obstacle crossing [6], [10], [11], [12]. Parkinson's disease is associated with reduced harmonic ratios of head acceleration during gait, suggesting that people with PD have a less rhythmic gait and less stable gait than unimpaired people of the same age [11]. Adkin et al. [6] also showed that people with moderately severe PD had abnormal trunk sway during a range of clinical and gait tasks. These tasks included self-paced walking, standing up from a chair and responding to a push or pull.

Our previous work has shown that people with PD walk slowly with short steps during level-ground walking [13] and obstacle crossing [10]. In one sample people with PD were found to widen their steps and spend more time in double limb support when they were required to walk over an obstacle. These gait changes were argued to be a compensatory mechanism to allow the person to gain greater stability in order to prevent falls [10].

It is unclear how PD affects mediolateral stability of centre of mass (CoM) motion in challenging tasks such as walking over obstacles. It also remains to be seen whether postural abnormalities when walking over obstacles are related to the severity of motor symptoms in people with PD. In line with the findings that PD usually results in a poverty of movement [13], [14], this study tested the hypothesis that people with PD have reduced and slower mediolateral CoM motion than controls during both level-ground walking and obstacle crossing. It was also hypothesised that increased severity of PD motor symptoms would be associated with reduced speed and size of mediolateral CoM motion during both level-ground walking and obstacle crossing.