A system for the continuous measurement of ankle joint moment in hemiplegic patients wearing ankle-foot orthoses.

Plastic ankle-foot orthoses (PAFOs) are now commonly used in clinical practice to supplement the gait disabilities of hemiplegic patients. However, few biomechanical investigation have been performed to analyze the corrective functions of PAFOs. In this paper, a measuring system was developed to assess the effect of dorsi/plantar flexibility of a PAFO on patient's gait. First, a mathematical model of gait with a PAFO was established so that the overall ankle joint moment can be separated into the muscle moment and the corrective moment generated by a PAFO. An experimental AFO, which simulates PAFOs, was specially designed and fabricated to continuously measure the corrective moment of the experimental AFO during gait. A device was also developed to continuously measure the overall ankle joint moment, so that the muscle moment can be estimated from the data obtained by the two devices. The measurement accuracy of the device was evaluated using gait data of eight healthy subjects who simulated hemiplegic gait. The range of the mean +/- 1 SD of the errors, calculated for the eight subjects, fell within +/- 5 Nm, which well compares with the error of commonly used comprehensive gait analysis systems.