Quantifying the variability of a complex motor task specifically studying the gait of dyskinetic CP children

Lately, more and more interest has been directed towards the variability of complex motor tasks and its diagnostic value in motion disorders. However, there is no standardized way of quantifying variability of motion. In this respect, the purpose of this study is to explore the usefulness of variability computations derived from three-dimensional (3D) motion trajectories. A mathematical and computational algorithm was defined to first extract and overlay the 3D data for the trajectories. As an example for the application, the trajectories of the ankle marker representing the motion during swing were chosen. The method was used to determine the variability during swing for CP children with and without dyskinesia (n=31). A group of healthy adult normals served as control (n=8). The results were validated against the visual rating of swing variability by experienced clinical observers. The calculated values were superior to the previously used pelvic span/ankle spread ratio. The proposed method of quantifying the variability of a complex, repetitive motor task proved to be valid and useful. It has no limitation with regard to reprocessing previously collected data, or as to which equipment is used to gather the 3D coordinates during the motion.