Muscle stretch receptor hypersensitization in spasticity. Inapproprioception, Part III.
Am J Phys Med, 57 (1):
16--28 (February 1978)Abstract
The author's concept of Inapproprioception, which accounts for athetoid movements in terms of defective proprioceptive feedback (i.e., distortion of afferent signals representing limb position) is extended here to explain spasticity in cerebral palsy was well. Descending activation of gamma efferents supplying hypertonic muscles may be excessive, leading to hypersensitization of stretch receptors in those muscles (the exact distribution of muscles affected varying with the individual). The result is exaggerated reflex activation of alpha motoneurons in response to the slightest muscle stretch. Even passive tension due to gravitational forces, which is inescapable, results in excessive impulse discharge from sensitized stretch afferents and thus leads to reflex contractions simply in response to shifts in body position. The affected muscles shorten to a length corresponding to the elevated level of reflexly originating motoneuron discharge, manifesting excessive tone even in the contracted state. The distribution of hypertonicity thus induced usually follows a predictable pattern and can be modified using slow passive stretch of hypertonic muscles to relax them, followed by facilitated voluntary contraction to strengthen weak antagonists, and progressing to functional reciprocal usage of agonists and antagonists to achieve proper muscle balance. Application of this procedure leads to improved posture, balance and ambulation in subjects with spastic cerebral palsy.