FES and spasticity

A model of hemiplegic spasticity based on parameters measured during passive muscle stretching is presented. Two components of spasticity can be distinguished: phasic and tonic. The classification depends on the pattern of stretch reflex activity which can be either phasic or tonic as well as on the muscle stretch/tension characteristic. Stretch reflex, as a control loop, is in phasic spasticity characterized by increased sensitivity to velocity stretching. In tonic spasticity, sensitivity to length of stretching is increased. After the injury, phasic spasticity appears first and invokes monosynaptic reflex pathways. The intensity of tonic spasticity increases with the duration of disability and hence causes changes in muscle fiber biomechanical properties. The model has been used to evaluate the effects of FES on spasticity. Hemiplegic patients with the implanted peroneal nerve stimulator for gait correction were observed for one year starting a week before implantation. Long-term use of FES resulted in decrease of tonic spasticity in both ankle joint antagonistic muscle groups.