Contribution of thixotropy, spasticity, and contracture to ankle stiffness after stroke

OBJECTIVES—Increased resistance to stretch of muscles after stroke may be the result of centrally mediated neural factors such as spasticity or local, peripheral factors such as muscle contracture or thixotropy. 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 stiffness after stroke.
METHODS—Thirty patients with stroke whose calf muscles were assessed clinically as stiff and 10 neurologically normal subjects were recruited. To measure thixotropy, 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 defined as the presence of tonic stretch reflexes in relaxed muscles. Contracture was defined as being present when maximum 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 stiffness while spasticity made a significant contribution (p=0.004) to the laboratory measure of calf muscle stiffness.
CONCLUSIONS—Measuring thixotropy at the level of joint movement was sufficiently sensitive to determine the thixotropic 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 stiffness. Contracture did significantly contribute to muscle stiffness, supporting the importance of prevention of contracture after stroke. Spasticity contributed to muscle stiffness only when the limb was moved quickly.


In vivo muscle morphology comparison in post-stroke survivors using ultrasonography and diffusion tensor imaging.

Skeletal muscle architecture significantly influences the performance capacity of a muscle. A DTI-based method has been recently considered as a new reference standard to validate measurement of muscle structure in vivo. This study sought to quantify muscle architecture parameters such as fascicle length (FL), pennation angle (PA) and muscle thickness (tm) in post-stroke patients using diffusion tensor imaging (DTI) and to quantitatively compare the differences with 2D ultrasonography (US) and DTI. Muscle fascicles were reconstructed to examine the anatomy of the medial gastrocnemius, posterior soleus and tibialis anterior in seven stroke survivors using US- and DTI-based techniques, respectively. By aligning the US and DTI coordinate system, DTI reconstructed muscle fascicles at the same scanning plane of the US data can be identified. The architecture parameters estimated based on two imaging modalities were further compared. Significant differences were observed for PA and tm between two methods. Although mean FL was not significantly different, there were considerable intra-individual differences in FL and PA. On the individual level, parameters measured by US agreed poorly with those from DTI in both deep and superficial muscles. The significant differences in muscle parameters we observed suggested that the DTI-based method seems to be a better method to quantify muscle architecture parameters which can provide important information for treatment planning and to personalize a computational muscle model

Evaluating the contribution of a neural component of ankle joint resistive torque in patients with stroke using a manual device

Primary objective: to investigate the methodology using a manual ankle joint resistive torque measurement device to evaluate the contribution of the neural component of ankle joint resistive torque in patients with stroke. Research design: Within-subject comparison to compare the ankle joint resistive torque between fast and slow stretching conditions. Methods and procedures: Ten patients with stroke participated in this study. The incremental ratio of ankle joint resistive torque at the ankle angular position of 5°° dorsiflexion under the fast stretching condition in comparison to the slow one was calculated in each patient. Main outcomes and results: A significant increase ( p < 0.01) in the ankle joint resistive torque was demonstrated under the fast stretching condition in comparison to the slow one in all patients and the mean ankle joint resistive torque was 4.6 (SD == 1.7) Nm under the slow stretching condition, while it was 8.4 (SD == 4.1) Nm under the fast stretching condition at the ankle angular position of 5°° dorsiflexion. The incremental ratio ranged from 9.4--139.3%% among the patients. Conclusions: The results of this study demonstrated the potential advantage of the device to evaluate the contribution of the neural component of ankle joint resistive torque