Analysis of trunk movement in orthotic gait of paraplegics

In an orthotic gait of paraplegics, a leg restriction and motor paralysis result in a significant loading. In this study, we address to quantify a relationship between the loading, leg restriction and motor paralysis, and analyze lumbar joint trajectories in the orthotic gait of paraplegic subjects and the ordinary and orthotic gaits of a normal subject using an inverted pendulum model. For the leg restriction, the trajectories are located anterior to an equilibrium point of the inverted pendulum, and the loading is higher due to the influence of gravity moment. Comparing the orthotic gait kinematics of paraplegic with that of normal in the horizontal plane, the lumbar joint trajectory in the paraplegic subjects was rectilinear shape, while that in the normal subject was curved in the direction to the equilibrium point. The loading is lower in the curved trajectory than in the straight trajectory because of the trade-off between gravity and inertia. These results suggest that the leg restriction and motor paralysis lead to the increase of the distance between the trunk movement and the equilibrium point of an inverted pendulum, which causes significant loading in the orthotic gate of paraplegics.