FES and spasticity.

A model of hemiplegic spasticity based on electromyographical and biomechanical parameters measured during passive muscle stretching is presented. Two components of spasticity can be distinguished--phasic and tonic. This 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 of 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 mentioned above has been used to evaluate the effects of FES on spasticity. Hemiplegic patients with implanted peroneal nerve stimulator for gait correction were followed up 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. In stimulated tibialis anterior muscle, the phasic type of spasticity increased. To obtain the correlation between changes in spasticity and functional abilities of patients, the maximal voluntary isometric contraction of both muscle groups was also measured. An improvement in voluntary strength was also observed. This can be taken as additional evidence that tonic spasticity is of greater physiological and clinical significance than phasic spasticity. It may be concluded that use of FES can decrease tonic spasticity and, if applied early after the injury, can prevent the appearance of tonic spasticity.