Dynamic gait stability for powered gait orthosis

Abstract

In human walking, the dynamic stability is achived by the automatic control using the body segments to prevent the falling, but PGO may not be sufficient to control the dynamic stability. Therefore, the quantitative approach would be required to evaluate the dynamic stability of paraplegic patients with PGO. Analysis of CoM and CoP is the classical method for human walking. D.A Winter first proposed a CoM analysis method, which is widely used. The movement of CoM and CoP contains a lot of information about stability. However, the previous CoM method is not a quantitative analysis about whether the distance between the CoM and the CoP can be used to determine a falling. It means that the CoM movement is only considered in a static analysis, thus the CoM analysis may not be good for the stability assessment. In this study, the dynamic stability for PGO gait was determined by using a ZMP method. Ten paraplegic patients participated in the experiment to determine the kinematics of PGO. The dynamic stability in PGO gait was compared with that in the normal gait.The characteristics of CoM and ZMP were investigated during normal and PGO gait. On sagittal plane, the ZMP and the CoM in PGO gait was dynamically stable, and 78.9% of the ZMP position was located in the SP during a gait cycle. On frontal plane, the ZMP was dynamically stable in double-limb-support phase, but not in single-limb-support phase. The propulsion force for the forward movement was from the deviation between the ZMP and the center of SP, and it could be calculated. This can be explained by results of the previous study that the propulsion force resulted from the deviation between the stance foot and the CoM in terminal stance phase. The CoM and the ZMP should move to the left foot and right foot in single-limb-support phase, but ZMP did not go into the SP in PGO gait. As the results, double-limb-support phase increased three times, and then gait stability might be secured. 90.5% of the ZMP position was located in the SP during a gait cycle.In this study, the PGO was designed to control the dynamic stability for paraplegic walking. As the experimental results, the energy consumption with PGO decreased significantly compared with RGO. The ZMP can be used as a dynamic stability parameter for paraplegic walking.