A Procedure for Measuring Anterior Scalene Morphology and Quality with Ultrasound Imaging: An Intra- and Inter-rater Reliability Study

Objective: Ultrasound (US) imaging is an essential tool for clinicians because of its cost-effectiveness and accessi-bility for assessing multiple muscle metrics including muscle quality, size and shape. Although previous studies highlighted the importance of the anterior scalene muscle (AS) in patients with neck pain, studies analyzing the reliability of US measurements for this muscle are lacking. This study aimed to develop a protocol for assessing AS muscle shape and quality measured with US and investigating its intra-and inter-examiner reliability.Methods: Through use of a linear transducer, B-mode images of the anterolateral neck region at the C7 level were acquired in 28 healthy volunteers by two examiners (one experienced and one novel). Cross-sectional area, perim-eter, shape descriptors and mean echo-intensity were measured twice by each examiner in randomized order. Intra-class correlation coefficients (ICCs), standard errors of measurement and minimal detectable changes were calculated.Results: Results indicated no muscle side-to-side asymmetries (p > 0.05). Gender differences were found for mus-cle size (p < 0.01), but muscle shape and brightness were comparable (p > 0.05). Intra-examiner reliability was good to excellent for all metrics for the experienced and (ICC >0.846) and novel (ICC >780) examiners. Although inter-examiner reliability was good for most of the metrics (ICC >0.709), the estimates for assessing solidity and circularity were unacceptable (ICC <0.70).Conclusion: This study found that the described ultrasound procedure for locating and measuring anterior scalene muscle morphology and quality is highly reliable in asymptomatic individuals.