Abstract
In paraplegic standing using functional electrical stimulation (FES), closed-loop control systems have been studied to maintain knee joint in extended position with least muscle contractile force. In this case, the selection of the controlled variable is important. Muscle force is considered to be useful as a controlled variable. However, there is no clinical method of directly measuring muscle force during motion. Hence, we used the tension of the patellar ligament as a controlled variable which reflects the contractile force of the knee extensor (the quadriceps femoris). In this study, a new method is proposed to estimate the tension of the patellar ligament. We estimated the tension of the patellar ligament by measuring the patellar ligament reaction force (PLRF) using the force transducer pushing the patellar ligament through skin. The following results were obtained in paraplegic experiments. The linear relationship existed between PLRF and the knee extension torque, and the transient response of the PLRF was similar to that of the knee extension torque. The PLRF had the good reproducibility, after a few prior stimulation to the muscle. The closed-loop control using PLRF maintained the knee extension torque above the desired value.
