Design of a Portable Functional Electrical System for Foot Drop Patients

Abstract

A portable functional electrical stimulation system has been designed using embedded systems technology. The system, which was applied to patients suffering from foot drop, uses sensors to monitor foot movement and orientation in a unique way, uses sophisticated algorithms for feedback, and drives an array of surface electrodes for stimulation. A new technique was invented based on using the twitch response of muscles to optimize the configuration of the electrode array. This reduces the setup time in the clinic. The feedback is used from the sensors and the optimum configuration of electrodes is chosen to produce correct stimulation and movement in real time. The instrument presents the patient with a ranked list of electrode combinations that are likely to be optimum, the patient can then choose a combination that is both effective and comfortable. The system can change the pattern of electrodes and also the stimulation signal during the process of stimulation. This may enable some problems associated with fatigue and skin irritation to be reduced. Trials were carried on 10 controls and 2 patients to test the instrument and study and develop the system optimization and control algorithms. These preliminary clinical trials showed that control of the stimulation during walking, based on the optimization algorithms developed in this work, gives high quality correction of foot drop. This was shown by gait assessment analysis by the physiotherapists earlier in the project. These trials prove that the concept of using the electrode array for stimulation has advantages over using a conventional 2- electrode system. The system has been designed and developed for the mentioned problem and has been tested for its efficacy.