Distinguishing active from passive components of ankle plantar flexor stiffness in stroke, spinal cord injury and multiple sclerosis

Lorentzen, Jakob, Grey, Michael J, Crone, Clarissa, Mazevet, Dominique, Biering-Sørensen, Fin and Nielsen, Jens B (2010) Distinguishing active from passive components of ankle plantar flexor stiffness in stroke, spinal cord injury and multiple sclerosis. Clinical Neurophysiology, 121 (11). pp. 1939-1951. ISSN 1388-2457

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Abstract

Objective: Spasticity is a common manifestation of lesion of central motor pathways. It is essential for correct anti-spastic treatment that passive and active contributions to increased muscle stiffness are distinguished. Here, we combined biomechanical and electrophysiological evaluation to distinguish the contribution of active reflex mechanisms from passive muscle properties to ankle joint stiffness in 31 healthy, 10 stroke, 30 multiple sclerosis and 16 spinal cord injured participants. The results were compared to routine clinical evaluation of spasticity. Methods: A computer-controlled robotic device applied stretches to the ankle plantar flexor muscles at different velocities (8–200 deg/s; amplitude 6°). The reflex threshold was determined by soleus EMG. Torque and EMG data were normalized to the maximal torque and EMG evoked by supramaximal stimulation of the tibial nerve. Passive resistance (the torque response to stretches) was confirmed to be a good representation of the passive stiffness also at higher velocities when transmission in the tibial nerve was blocked by ischemia. Results: Passive torque tended to be larger in the neurological than in the healthy participants, but it did not reach statistical significance, except in the stroke group (p < 0.05). Following normalization to the maximal stimulus-evoked torque, the passive torque was found to be significantly larger in neurological participants identified with spasticity than in non-spastic participants (p < 0.01). There was no significant difference in the reflex threshold between the healthy and the neurological participants. The reflex evoked torque and EMG were significantly larger in all neurological groups than in the healthy group (p < 0.001). Twenty three participants with evidence of hypertonia in the plantar flexors (Ashworth score ⩾ 1) showed normal reflex torque without normalization. With normalization this was only the case in 11 participants. Increased reflex mediated stiffness was detected in only 64% participants during clinical examination. Conclusion: The findings confirm that the clinical diagnosis of spasticity includes changes in both active and passive muscle properties and the two can hardly be distinguished based on routine clinical examination. Significance: The data suggest that evaluation techniques which are more efficient in distinguishing active and passive contributions to muscle stiffness than routine clinical examination should be considered before anti-spastic treatment is initiated.

Item Type: Article
Additional Information: Copyright © 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.
Uncontrolled Keywords: stretch reflexes,spasticity
Faculty \ School: Faculty of Medicine and Health Sciences > School of Health Sciences
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Depositing User: Pure Connector
Date Deposited: 27 Jun 2017 05:06
Last Modified: 31 Oct 2019 15:12
URI: https://ueaeprints.uea.ac.uk/id/eprint/63858
DOI: 10.1016/j.clinph.2010.02.167

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