抄録
Desirable characteristics of ankle-foot orthoses (AFOs) for hemiplegic patients were clarified by the authors' previous studies. The most important mechanical characteristics of AFOs are the magnitude of the dorsiflexion assist moment and the initial ankle angle. It is necessary to adjust these characteristics to the individual hemiplegic patient. It was also found that the plantar flexion assist moment generated by conventional AFOs is not necessary, but rather is injurious to the hemiplegic gait. An AFO called DACS AFO, which means Dorsiflexion Assist Controlled by Spring AFO, was developed to incorporate these characteristics. The DACS AFO consists of two plastic parts, the foot and the shank, connected at the ankle joint. An assist device that generates the dorsiflexion assist moment is set at the rear of the shank. When the ankle joint rotates into plantar flexion, a piston compresses the spring and the assist device generates an assist moment proportional to the plantar flexion angle. The dorsiflexion assist moment can be changed easily by using four different kinds of springs. When the ankle joint rotates into dorsiflexion, it rotates freely because a slider in the piston can move without friction. The initial ankle angle can be changed by altering the length of the assist device. The weight of the assist device is 70 grams. The gait of hemiplegic patients with DACS AFOs, with conventional posterior AFOs, and without any AFOs were measured by a three-dimensional motion analysis system (Oxford Metrics VICON 370 and force plates). Before the gait analysis, the characteristics of the DACS AFO were adjusted to the condition of each patient through observation of the gait. The gait cycle decreased and walking velocity increased when patients walked with DACS AFOs. The maximum magnitude of the plantar flexion ankle joint moment increased when the patients walked with DACS AFOs although the DACS AFOs did not generate any plantar flexion assist moment. This result means that the ankle joint moment generated by the plantar flexors increases because of the smooth propulsion of the center of gravity of the body during the mid to late stance. The performance of the DACS AFO was assessed through daily use by approximately 70 hemiplegic patients. The acceptance by patients was good but some defects were clarified, such as weight, appearance, and noise during gait.We intend to improve them and to put the DACS AFO on the market.
