OBJECTIVES—Increasedresistance to stretch of muscles after stroke may be the result ofcentrally mediated neural factors such as spasticity or local,peripheral factors such as muscle contracture or thixotropy. The aimwas to investigate evidence for an abnormal thixotropic response andcompare this with two other factors—contracture and spasticity—whichcould potentially contribute to muscle stiffness after stroke. METHODS—Thirtypatients with stroke whose calf muscles were assessed clinically asstiff and 10 neurologically normal subjects were recruited. To measurethixotropy, their calf muscles were stretched through two cycles aftertwo prestretch conditions: one in which the muscles were maintained ina shortened position and one in which they were maintained in alengthened position. Spasticity was defined as the presence of tonicstretch reflexes in relaxed muscles. Contracture was defined as beingpresent when maximum passive ankle dorsiflexion fell at least 2 SDbelow the mean value of the control subjects. RESULTS—Both controlsand patients with stroke exhibited a thixotropic response but this wasno greater in the patients than the controls. About one third of thepatients displayed muscle contracture and most exhibited spasticity.Contracture made a significant contribution (p=0.006) to the clinical measure of calfmuscle stiffness while spasticity made a significant contribution(p=0.004) to the laboratory measure of calfmuscle stiffness. CONCLUSIONS—Measuringthixotropy at the level of joint movement was sufficiently sensitive todetermine the thixotropic response in both neurologically normalsubjects and patients impaired after stroke. The thixotropic responsewas not higher than normal after stroke, suggesting that whereasthixotropy may produce enough immediate resistance to impede movementin those who are very weak, it is not a substantial contributor to longterm muscle stiffness. Contracture did significantly contribute tomuscle stiffness, supporting the importance of prevention ofcontracture after stroke. Spasticity contributed to muscle stiffnessonly when the limb was moved quickly.
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