Shear-wave elastography for assessment of trapezius muscle stiffness: Reliability and association with low-level muscle activity.

Žiga Kozinc,Nejc Šarabon,Dragan Mirkov

doi:10.1371/journal.pone.0234359

Abstract

PurposeShear-wave elastography has been recognized a useful tool for quantifying muscle stiffness, commonly reported as shear modulus, however the reports on reliability are often limited to test-retest correlations. In this study, we explored the reliability of shear-wave elastography for assessment of the trapezius muscle stiffness and its relationship with low-level muscle activity.MethodsTwenty participants were included in a two-session experiment. Measurements of shear modulus and muscle activity were performed at rest and during low-level activity, induced by shoulder abduction without additional external resistance.ResultsGood to excellent intra-session repeatability (ICC > 0.80) and moderate inter-rater and inter-session reproducibility (ICC = 0.66–0.74) were observed. Typical errors were acceptable (7.6% of the mean value) only for intra-session measurements in resting conditions, but not acceptable for all conditions with low-level muscle activity (10.2–16.6% of the mean value). Inverse relationships between shear modulus and muscle activity at 40° and 60° of shoulder abduction (r = -0.53 and -0.57) were observed on a group level. We also found higher shear modulus in males compared to females, for the parallel probe position compared to the perpendicular position (in relation to muscle fiber orientation), and for the dominant side of the body compared to the non-dominant side.ConclusionsThis study showed an inverse relationship between muscle activity in low-level range and shear modulus on a group level, suggesting inherent passive stiffness could account for a larger portion of the variance (compared to muscle activity) in shear modulus when the muscle activity is low. Our results imply that shear-wave elastography can be used in research exploring muscle stiffness, however, caution is needed since only intra-session examination in resting conditions showed acceptable within-participant typical errors. The secondary analyses of the study showed higher shear modulus for males, for the non-dominant side of the body and for the parallel orientation of the ultrasound probe.

Highlights

Shear-wave elastography (SWE) is a relatively novel ultrasound method for assessing mechanical properties of body tissues [1,2]
We found higher shear modulus in males compared to females, for the parallel probe position compared to the perpendicular position, and for the dominant side of the body compared to the non-dominant side
Strong withinindividual associations were shown between shear modulus values and muscle activity or muscle force [9,12,15]

Summary

Introduction

Shear-wave elastography (SWE) is a relatively novel ultrasound method for assessing mechanical properties of body tissues [1,2]. In addition to real-time imaging, modern ultrasound devices that utilize SWE technique enable quantification of tissue stiffness, expressed as shear modulus (kPa). A growing body of literature demonstrates the utility of SWE method for assessing muscle stiffness [3,4,5,6,7,8,9,10,11,12]. The shear modulus obtained with SWE has been validated for assessing muscle stiffnes, by using isolated meat speciments and comparing it to direct mechanical stiffness measures. Strong withinindividual associations were shown between shear modulus values and muscle activity or muscle force [9,12,15]

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