Equilibrium point model of knee joint spasticity

Spasticity is a highly complex phenomenon, which has not been defined in precise and quantifiable terms. Although the muscle stretch reflex is thought to play an important role in spasticity generation, the pathophysiologic basis of spasticity is not completely understood. Utilizing Wartenberg´s pendulum knee test, this research demonstrates that spasticity can be modeled as a disorder of equilibrium point control. The Equilibrium Point Hypothesis of motor control theorizes that the central nervous system (CNS) provides a virtual trajectory of joint motion, representing space and timing. A mathematical model has been developed that can reproduces kinematic data through the use of dynamic optimization techniques. The results of this study support the concept that spasticity may be part a disorder in which the virtual trajectory specified by the CNS is distorted.