Relative and absolute reliability of ultrasound measurements for the thickness of the soft tissue around the shoulder joint of young normal subjects

[Purpose] The purpose of this study was to examine the reliability of ultrasound measurements by analyzing the relative reliability and absolute reliability when measuring soft tissue thickness around the shoulder joint. [Subjects and Methods] Eleven healthy young adults (22 shoulders) participated in this study. Thickness of the supraspinatus tendon, subacromial bursa, and biceps tendon was measured on both shoulders. This protocol was performed twice in the same day. The relative reliability of ultrasound measurement was evaluated using the intraclass correlation coefficient for determining the degree of consistency and agreement between two measures. The absolute reliability of the ultrasound measurement was evaluated using the standard error of measurement, minimum detectable change, and Bland-Altman analysis. [Results] Ultrasound measurements exhibited high relative reliability: intraclass correlation coefficients for the supraspinatus tendon, subacromial bursa, and biceps tendon thickness were demonstrated to be 0.91, 0.82, and 0.90, respectively. Bland-Altman analyses revealed no significant systematic bias between the repeated measurements for the supraspinatus tendon, subacromial bursa, and biceps tendon thickness. [Conclusion] These findings suggest that ultrasound measurement for the supraspinatus tendon, subacromial bursa, and biceps tendon thickness exhibited good relative reliability and no systematic errors were detected regarding their absolute reliability.