Reproducibility of ultrasonographic thickness measurements of the common lateral extensors of the elbow

Abstract

Background: In individuals with clinical appearances of lateral elbow tendinopathy, the thickness of the common lateral extensors tendon is commonly evaluated by musculoskeletal ultrasonography. To date, the inter- and intra-rater reliability and intra-rater agreement of objective thickness measurements, in longitudinal as well as in transversal plane, are unknown. The reproducibility of these thickness measurement, by a standardized measurement protocol, should be established before it can be integrated into daily practice and study protocols. Objective: To determine the inter- and intra-rater reliability and intra-rater agreement of musculoskeletal ultrasound thickness measurements of the common lateral extensors tendon of the elbow in the longitudinal and transversal plane in healthy adults. Study design: A test-retest design. Methods: The thickness of the common lateral extensors tendon was measured by ultrasonography in the longitudinal and transversal plane. Each participant was measured two times by rater 1 and rater 2, using a standardized protocol. Reproducibility was assessed by the intraclass correlation coefficient (ICC) and the smallest detectable change (SDC). Results: Seventy-three healthy individuals participated in the study (44% females) with a mean ± SD age of 35.7 ± 14.9 years. Inter-rater reliability for both the longitudinal and transversal plane were fair to good (ICC of 0.67 and 0.49 respectively). ICC values for intra-rater reliability varied between fair to good and excellent (ICC of 0.73-0.92). P-values were < 0.05 in all cases. The SDC for both raters, as well as for the longitudinal and transversal plane, ranged from 0.50 to 0.78 mm and comprised 9.8-16.3% of the mean thickness. Conclusion: Objective musculoskeletal ultrasonographic thickness measurement of the common lateral extensors tendon of the elbow has fair to excellent intra- and inter-rater reliability. In addition, agreement is acceptable, which makes musculoskeletal ultrasound a valuable tool for the evaluation of treatment effects on tendon thickness over time.