Ultrasound imaging of quadriceps muscle in patients with knee osteoarthritis: The test-retest and inter-rater reliability and concurrent validity of echo intensity measurement

Background: Echo intensity(EI) on ultrasonography images of skeletal muscle reflects muscle composition. Objectives: The primary aim of the study was to investigate the inter-rater and test-retest reliability of EI using grayscale histogram analysis of the cross-sectional area of quadriceps femoris(QF) muscle in patients with knee osteoarthritis(KOA). The secondary aim of the study was to determine the concurrent validity of the Free Hand Tool(FHT) when compared to Rectangular Marquee Tool(RMT) for calculating the region of interest(ROI) in ImageJ. Methods: This study included thirty patients with KOA. Echogenicity of the QF muscle were performed by two different raters. The reliability analysis was applied using intraclass correlation coefficient(ICC), standard error of measurement(SEM) and coefficient of variation(CV). Spearman rank correlation coefficients were calculated for assessing concurrent validity of the FHT to RMT. The Bland-Altman plots was used to show disagreement between tools. Wilcoxon signed-rank test was used for differences in assessments between test/retest sessions, raters, tools. Results: The inter-rater and test-retest reliability of the EI using FHT and RMT was found to be excellent (ICCFHT = 0.91-0.95, 0.98-0.99, ICCRMT = 0.91-0.98, 0.91-0.99,respectively). Bland-Altman analysis demonstrated a slight bias when region ROI calculations were collected from RMT or FHT (bias ranging from 2.75 to 2.40 a. u). There were no significant differences between test/retest sessions, raters and tools(p > 0.05). Spearman correlation coefficient showed excellent correlation between tools used for echogenicity assessment of QF muscle(p < 0.001). Conclusion: EI assessment using ultrasonography in the QF muscle showed excellent reliability. Evaluating muscle echogenicity using both FHT and RMT appears to be reliable and validity for monitoring muscle changes due to KOA.