Dynamics of turning sharpness influences freezing of gait in Parkinson's disease.

Background: Despite the strong association between turning and Freezing of gait (FOG) in Parkinson's disease (PD), there has been little research to evaluate the specific turn characteristics (i.e. turn angles) that might contribute to freezing. Therefore, the purpose of the present study has three

Aims: examine the turning gait kinematics in freezers, evaluate the prevalence of FOG at different turn angles, and characterize whether the specific turning strategies employed by PD patients might be associated with turning deficits.

Methods: 20 PD participants (10 freezers, 10 non-freezers) and 10 healthy controls walked down a 6-m pathway and completed randomized trials of 0°, 90°, 120°, and 180° turns. Spatiotemporal gait kinematics were analysed using motion capture, while presence of FOG and classification of turn types (step out, crossover, or mixed strategy) were identified by two independent raters using video analysis.

Results: Freezers significantly increased step time variability and elicited more freezing episodes at sharper turns. Healthy controls consistently implemented a crossover turning strategy for all turning angles, while freezers tended to use a step out and mixed strategy especially during 180° turns. This strategy in freezers was associated with a failure to increase step width (as healthy controls do). Additionally, in contrast to healthy controls and non-freezers, a dramatic decrease in velocity was identified in freezers for all turning angles.

Conclusions: Freezing episodes are associated with a deficit in controlling gait timing. Additionally, freezers fail to increase step width despite employing a safer turn strategy.