Reliability and agreement of speckle-tracking ultrasonography for assessing muscle function of the rotator cuff in patients with subacromial pain syndrome

Objective Shoulder pain mainly originates from subacromial pain syndrome (SAPS), with the supraspinatus (SS) and infraspinatus (IS) muscles most often affected. Speckle-tracking ultrasonography (STU) is a non-invasive method to quantify muscle deformation. However, reliability and agreement with software post-processing procedures (inter-rater) and symptom-related variance (test-retest) for the same rater are unknown. This study aimed to assess the inter-rater reliability and agreement of STU post-processing procedures and the test-retest reliability and agreement of STU for evaluating SS and IS muscle function in patients with SAPS and a healthy control group Methods Twenty-four SAPS patients were assessed for inter-rater and test-retest (+1 week) variability, with the addition of 22 matched (age/gender) controls for the test-retest analysis. STU recordings were post-processed using EchoPAC software. Reliability was assessed using the intra-class correlation coefficient (ICC) and minimal detectable change (MDC). Agreement was evaluated using Bland-Altman plots Results Inter-rater reliability for SAPS shoulders was good–excellent (ranges: ICC 0.87–0.97; MDC 1.4–2.2% strain) and test-retest poor–moderate (ranges: ICC 0.16–0.59; MDC 3.5–8.9% strain). For the controls, test-retest showed good–excellent reliability (ranges: ICC 0.83–0.96; MDC 1.8–3% strain). Agreement was high for SAPS shoulders between raters. Test-retest agreement was moderate for the controls and low for SAPS shoulders Conclusion STU showed excellent inter-rater reliability for post-processing strain measurements of the SS and IS muscles. However, test-retest reliability was low in SAPS patients, likely due to symptom-related variability. While STU shows promise for assessing muscle function, its clinical applicability and feasibility remain unexplored.