Design of an active orthosis controlling spasticity and contractures

Abstract During the project ACTOR an active orthosis to control spasticity and prevent contractures at the elbow joint in patients with stroke is developed. With an annual incidence of 200 to 300 per 100.000 inhabitants, stroke is the commonest cause of severe disability in Western countries.1 80% to 95% of patients with stroke do not show complete functional recovery of the hemiplegic arm and 38% of the patients develop spasticity in the first year.2,3 In addition to pain and contractures, spasticity is a major barrier for efficient rehabilitation and has an unfavourable impact on numerous activities of daily life. The increasing amount of patients and the relative decrease of therapists create a need for technological innovations compensating this imbalance and resulting in an increase in therapy time, repetitions and task specificity.4 The project ACTOR examines how an active assisted angular mobilisation therapy can be performed in an autonomous working system. EMG signals from m. biceps brachii and m. triceps brachii are used as input signals for the actuator control algorithm to guide the elbow flexion and extension movement, respectively. For each patient, an EMG threshold is defined that has to be exceeded during the whole range of motion (ROM) in order that the device assists the movement at a constant speed (10°/sec). In this way, active training of the patient can be ensured and, by increasing the threshold, training progression can be made. The ROM during this therapy is based on the passive ROM measured by a therapist. After proving the feasibility, the effectiveness of the device will be assessed by means of a clinical trial in which the effect on spasticity, active and passive ROM, muscle force and functional activities is investigated. This project will lead to a prototype preceding the development of a user-friendly, comfortable, safe and affordable rehabilitation device. Future potential can lie in the possibility to become a complement to traditional, labour- and time-intensive neurological rehabilitation to achieve a faster functional recovery of patients with stroke.status: publishe