Virtual Pivot Point Model Predicts Instability in Parkinsonian Gaits

The fear of falling due to changes in gait leads to a decrease in quality of life in Parkinson's patients. Also, Parkinson's patients require medical treatment due to falling each year. However, the reasons for the changed walking style still remain unknown. The goal of this study is the evaluation of possible reasons for the changed walking pattern in Parkinson's disease. A pilot study is conducted, which includes patient experiments, data analysis, and biomechanical modeling. Differences between Parkinsonian and healthy gait are detected and replicated by the model. The model represents simplified body dynamics and is optimized for healthy and Parkinsonian gait, respectively. Comparison measures are ground reaction forces, joint torques, and the virtual pivot point (VPP) location. The VPP is the intersection point of all forces throughout the gait cycle and is closely correlated to human balancing and stability. Parkinsonian gait showed different force and torque curves compared to healthy walking and a VPP below the center of mass location (negative VPP). The model represents healthy walking well. Specific Parkinsonian behavior can be explained by the changed modulation of the model. However, a negative VPP location turns the model unstable as, after two steps, the trunk tilts more than 90 degrees forward. Our modeling with negative VPP shows instability effects observed in Parkinson's patients walking who struggle with frequent stumbles and falls. Such modeling approaches could be used for developing new rehabilitation techniques and gait assistance devices.