Department of Biomedical Engineering
McGill University
Supervisor: Dr. R. Kearney
Abstract - Spasticity is defined as the abnormal muscle tone encountered when a muscle is passively stretched and is a common abnormality present after a stroke. Despite the prevalence of spasticity, the nature and origin of abnormal muscle tone giving rise to this joint stiffness is controversial. The major reason for this controversy is the difficulty in distinguishing the mechanical consequences of reflex activity from those due to passive tissues and active muscles. The purpose of this study was to describe ankle stiffness in stroke patients using system identification, which is an objective method of separating the reflex and intrinsic stiffness components.
We studied stroke patients with clinical evidence of ankle spasticity and compared them with gender- and age-matched controls. Subjects lay supine with their foot attached to an electro-hydraulic actuator by a custom-fitted boot. Series of pseudo-random binary sequences of 0.03 rads amplitude were used to rotate the ankle at different initial positions. The reflex and intrinsic contributions were separated with the parallel-cascade system identification method.
The results of this study showed that ankle stiffness was increased in stroke patients, and was mostly due to the reflex stiffness component. Furthermore, the changes in reflex stiffness varied with position, and stroke subjects demonstrated more stiffness as the ankle was dorsiflexed. The reflex gain was the parameter that explained the increase in the reflex stiffness in stroke patients.