Measuring mechanical properties of spastic muscles after stroke. Does muscle position during assessment really matter?

Abstract

Objective: To investigate the influence of muscle position (relaxed vs stretched) on muscle mechanical properties and the ability of myotonometry to detect differences between sides, groups, and sites of testing in patients with stroke. We also analyzed the association between myotonometry and clinical measures of spasticity. Design: Cross-sectional study. Setting: Outpatient rehabilitation units including private and public centers. Participants: Seventy-one participants (20 subacute stroke, 20 chronic stroke, 31 controls) were recruited (N=71). Intervention: Muscle mechanical properties were measured bilaterally with a MyotonPRO at muscle belly and musculotendinous sites during 2 protocols (muscle relaxed or in maximal bearable stretched position). Main Outcome Measures: Muscle tone and stiffness of the biceps brachii and gastrocnemius. Poststroke spasticity was evaluated with the Modified Tardieu Scale (MTS). A mixed-model analysis of variance was used to detect differences in the outcome measures. Results: The analysis of variance showed a significant effect of muscle position on muscle mechanical properties (higher tone and stiffness with the muscle assessed in stretched position). Measurements with the stretched muscle could help discriminate between spastic and nonspastic sides, but only at the biceps brachii. Overall, there was a significant increase in tone and stiffness in the chronic stroke group and in myotendinous sites compared with muscle belly sites (all, P<.05). No correlations were found between myotonometry and the MTS. Conclusions: Myotonometry assessment of mechanical properties with the muscle stretched improves the ability of myotonometry to discriminate between sides in patients after stroke and between people with and without stroke