Reliability of ultrasound imaging measures of soft tissue stiffness using elastography in the posterior aspect of the leg

Abstract

Objectives: To evaluate the intra- operator and inter- operator reliability of ultrasound elastography (UES) imaging in obtaining stiffness measurements of subcutaneous tissue, lateral gastrocnemius, and soleus muscles at rest.

Design: Single-group, repeated-measures, reliability study.

Participants: A convenience sample of 12 healthy adults (n=3 males, n=9 females, mean ± SD age = 28.9 ± 5.8 yrs, height = 169.6 ± 9.17 cm, weight = 69.6 ± 13.35 kg. Physical activity = 9 of the 12 failed to meet the definition of being ‘sufficiently active’) were enrolled in the study and examined in a single session by three operators: two novice UES operators with minimal previous experience, and an experienced operator with > 20 years of experience in musculoskeletal sonography.

Methods: UES imaging (acoustic radiation force impulse) was used to acquire elastograms of the subcutaneous tissue, lateral gastrocnemius and soleus muscle with participants lying prone with the ankle in neutral. Three examiners acquired images from all participants during a single session.

Main Outcome Measures: Mean colour-hue histograms were generated as a proxy measure of stiffness for the subcutaneous tissue, lateral gastrocnemius, and soleus muscle. Intraclass correlation coefficients (ICC, model 2, 1) and coefficients of variation (CV) were used to estimate reliability. Standard error of measurement and minimal detectable change were calculated to aid interpretation.

Results: Point estimates for intra-operator reliability were ‘high’ to ‘very high’ (ICC ranging from 0.59 to 0.85 across all tissues). All three operators demonstrated similar levels of intra-operator reliability. Inter-operator reliability estimates ranged between ‘trivial’ and ‘very high’ (ICC range: -0.07 to 0.87 across all tissues). The inter-operator values for subcutaneous tissue had the lowest test-retest reliability in comparison to gastrocnemius and soleus muscle.

Conclusions: Operators in this study demonstrated acceptable intra-operator reliability of UES measures, for stiffness of the subcutaneous tissue, lateral gastrocnemius and soleus muscle in healthy participants, however, inter-operator reliability ranged widely. Therefore, we suggest that UES (acoustic radiation force impulse) can be useful for clinical assessment when applied by both novice or/and experienced operators, when following our specific protocol. These findings indicate this technique could be potentially useful as a non-invasive measure of muscle stiffness in clinical and research settings.