Intra-rater and inter-rater reliability of the standardized ultrasound protocol for assessing subacromial structures

Background: US-examinations related to shoulder impingement (SI) often vary due to methodological differences, examiner positions, transducers, and recording parameters. Reliable US protocols for examination of different structures related to shoulder impingement are therefore needed. Objectives: To investigate the intra- and inter-rater reliability of the existing ultrasound (US) examinations of the subacromial space, the subacromial-subdeltoid bursa, and the supraspinatus tendon. Method: In a three-phased design, two physiotherapists using a standardized US protocol examined the thickness of the supraspinatus tendon (SUPRA) and subacromial subdeltoid (SASD) bursa in two imaging positions, and the acromial humeral distance (AHD) in one position. Additionally, agreement on dynamic impingement (DI) examination was performed. The intra- and inter-rater reliability was carried out on the same day. Participants: Forty-six sports active participants with a mean age of 37years (range 18-57) participated. Twenty-two had SI and pain within previous week and 24 did not have SI or pain within previous week. Results: Intra- and inter-rater reliability ICC (2,3) models were all above 0.80 (range 0.82-0.99) with no systematic bias (Bland Altman plots). For the DI examination, the overall agreement was 98% and 93%, with Kappa of 0.96 and 0.82, for intra- and inter-rater reliability, respectively. Conclusion: The reliability of the current standardized protocol for US examination of SI was excellent and considered feasible for clinical practice.