Spasticity

As has been said of certain forms of art, spasticity is difficult to define, but "You know it when you see it." After upper motoneuron damage due to spinal cord injury, spinal circuitry receives unbalanced input from peripheral afferent fibers and segmental interneuronal circuits relative to descending supraspinal pathways. This results in a mostly detrimental clinical syndrome of distorted motor control that contributes as much as frank weakness does to hindering execution of activities of daily living. In this chapter, we elaborate on our current understanding of the physiological mechanisms underlying post-SCI spasticity in humans, its evolution, its assessment, and a spectrum of clinical interventions. We end by discussing future directions of investigation that could position clinicians to help patients reestablish volitional control over the altered circuitry that underlies spasticity.