Reliability and Agreement of Ultrasonographic Thickness Measurements of the Common Lateral Extensors of the Elbow

In individuals with lateral elbow tendinopathy, the thickness of the common lateral extensors tendon can be evaluated by musculoskeletal ultrasonography (MSU) for diagnostic and evaluative purposes. The reproducibility of these thickness measurements should be established before integrating it into daily practice. A test-retest design was used to determine the reproducibility of these measurements in the longitudinal and transverse planes. Seventy-three healthy participants were measured two times by two raters. Intra-class correlation coefficient values for inter-rater reliability for the longitudinal and transverse planes were 0.67 and 0.49. Intra-class correlation coefficient values for intra-rater reliability varied between 0.73 and 0.92. The smallest detectable change ranged from 0.50 to 0.78 mm and comprised 9.8%-16.3% of the mean thickness. MSU thickness measurement of the common lateral extensors tendon of the elbow has fair to excellent intra- and inter-rater reliability. Additionally, agreement is acceptable, which makes MSU a valuable tool for the evaluation of tendon thickness over time.