Abstract
Postural instability, in particular at gait initiation (GI), and resulting falls are a major determinant of poor quality of life in subjects with Parkinson’s disease (PD). Still, the contribution of the basal ganglia and dopamine on the feedforward postural control associated with this motor task is poorly known. In addition, the influence of anthropometric measures (AM) and initial stance condition on GI has never been consistently assessed. The biomechanical resultants of anticipatory postural adjustments contributing to GI [imbalance (IMB), unloading (UNL), and stepping phase) were studied in 26 unmedicated subjects with idiopathic PD and in 27 healthy subjects. A subset of 13 patients was analyzed under standardized medication conditions and the striatal dopaminergic innervation was studied in 22 patients using FP-CIT and SPECT. People with PD showed a significant reduction in center of pressure (CoP) displacement and velocity during the IMB phase, reduced first step length and velocity, and decreased velocity and acceleration of the center of mass (CoM) at toe off of the stance foot. All these measurements correlated with the dopaminergic innervation of the putamen and substantially improved with levodopa. These results were not influenced by anthropometric parameters or by the initial stance condition. In contrast, most of the measurements of the UNL phase were influenced by the foot placement and did not correlate with putaminal dopaminergic innervation. Our results suggest a significant role of dopamine and the putamen particularly in the elaboration of the IMB phase of anticipatory postural adjustments and in the execution of the first step. The basal ganglia circuitry may contribute to defining the optimal referent body configuration for a proper initiation of gait and possibly gait adaptation to the environment.
Highlights
In the case of Parkinson’s disease (PD), locomotion is one of the functionally relevant daily acts that can be severely affected, especially at the initiation of movement
We first described disease-specific biomechanical abnormalities comparing PD patients with age- and gendermatched healthy subjects; we further showed the effect of a dopaminergic therapy and compared kinematic resultants of anticipatory postural adjustments (APA) with putaminal dopamine reuptake transporters (DAT) binding values
A preliminary but fundamental aim of this work was to investigate which measurements of the gait initiation (GI) motor performance are influenced by anthropometric measures (AM) and base of support (BoS)
Summary
In the case of Parkinson’s disease (PD), locomotion is one of the functionally relevant daily acts that can be severely affected, especially at the initiation of movement. Gait initiation (GI) greatly challenges the balance control system as the subject moves from a stable balance condition to unstable single limb support during locomotion This motor task can be impaired in parkinsonian patients due to start hesitation or gait freezing, leading to falls, injuries, fear of falling, and restriction of activities (Peterson and Horak, 2016). The UNL phase is the subsequent displacement of the CoP toward the stance foot, prominently in the mediolateral (ML) direction, needed to transfer the load onto the supporting foot and to allow the swing foot to clear the ground and make a step (Crenna and Frigo, 1991; Crenna et al, 2006)
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