Hemiplegic patients sometimes show three-dimensional abnormal movements during gait. This study focused on detecting abnormal gait movements of hemiplegic subjects with an inertial sensor. First, the estimation accuracy of the three-dimensional vector calculated from signals measured with the inertial sensor was evaluated using a metallic structure. As a result, adequate estimation accuracy was obtained. Then, using the estimated vector, the three-dimensional thigh movements of four hemiplegic subjects were compared with those of 12 healthy subjects. The average values of the range of vector components in the lateral direction of the three hemiplegic subjects were larger than those of healthy subjects. This suggests the circumduction movement of hemiplegic subjects. Therefore, the estimated thigh vector from inertial sensor signals is considered useful for detecting three-dimensional abnormality during hemiplegic gait. Further studies are required to develop a practical evaluation index.
