Intermachine Variation of Ultrasound Strain Elastographic Measures of the Quadriceps and Patellar Tendons in Healthy Participants

OBJECTIVES: To evaluate intermachine variation and compare intraoperator and interoperator agreement and repeatability characteristics of 2 ultrasound (US) systems for measurements of quadriceps and patellar tendons by strain elastography (SE). METHODS: Forty tendons from 20 healthy participants were investigated by operators with different experience (operator 1, 12 years of US experience and >50 SE examinations; operator 2, no US experience and 1 day of SE training). Repeated measures were performed on GE Healthcare (Waukesha, WI) and Esaote (Genoa, Italy) US systems. The percentage of agreement, Cohen kappa, intraclass correlation coefficient, and correlation tests assessed agreement, repeatability, and associations of SE measures. A paired t test and Wilcoxon signed rank test assessed differences in SE measures. RESULTS: The study participants included 5 male and 15 female volunteers (mean [range] age, 29.3 [21-39] years). Better agreement and repeatability characteristics were observed for the patellar compared to the quadriceps tendon and the color score (CS) method over the elasticity ratio (ER). Intraoperator agreement was better for the experienced operator. Intraoperator repeatability was achieved in 55% of ER (intraclass correlation coefficient, 0.40-0.91; P .5) patellar ER measures were observed. Seventy-four percent to 75% mean agreement (kappa = 0-0.5) for CS measures comparable across both US systems was observed. Intermachine ER associations were poor (r = -0.39-0.13; P > .05), whereas greater than 70% agreement (kappa = -0.87-0.53) for the CS was achieved. CONCLUSIONS: The reproducibility of knee tendon SE measurements is influenced by the operator experience, US system, and tendon site.