Contribution of thixotropy, spasticity, and contracture to ankle stiffness after stroke. J Neurol Neurosurg Psychiatry 2000; 69

Objectives—Increased resistance to stretch of muscles after stroke may be the result of centrally mediated neural factors such as spasticity or local, peripheral fac-tors such as muscle contracture or thixot-ropy. The aim was to investigate evidence for an abnormal thixotropic response and compare this with two other factors— contracture and spasticity—which could potentially contribute to muscle stiVness after stroke. Methods—Thirty patients with stroke whose calf muscles were assessed clini-cally as stiV and 10 neurologically normal subjects were recruited. To measure thix-otropy, their calf muscles were stretched through two cycles after two prestretch conditions: one in which the muscles were maintained in a shortened position and one in which they were maintained in a lengthened position. Spasticity was de-fined as the presence of tonic stretch reflexes in relaxed muscles. Contracture was defined as being present when maxi-mum passive ankle dorsiflexion fell at least 2 SD below the mean value of the control subjects. Results—Both controls and patients with stroke exhibited a thixotropic response but this was no greater in the patients than the controls. About one third of the patients displayed muscle contracture and most exhibited spasticity. Contracture made a significant contribution (p=0.006) to the clinical measure of calf muscle stiV-ness while spasticity made a significant contribution (p=0.004) to the laboratory measure of calf muscle stiVness. Conclusions—Measuring thixotropy at the level of joint movement was suY-ciently sensitive to determine the thixo-tropic response in both neurologically normal subjects and patients impaired after stroke. The thixotropic response was not higher than normal after stroke, suggesting that whereas thixotropy may produce enough immediate resistance to impede movement in those who are very weak, it is not a substantial contributor to long term muscle stiVness. Contracture did significantly contribute to muscle stiVness, supporting the importance of prevention of contracture after stroke. Spasticity contributed to muscle stiVness only when the limb was moved quickly