Subacromial space measured by ultrasound imaging in asymptomatic subjects and patients with subacromial shoulder pain: an inter-rater reliability study.

BACKGROUND: Acromiohumeral distance (AHD) and supraspinatus tendon thickness (STT) measured by ultrasound (US) can be combined in the occupation ratio (OR). Inter-rater reliability on these subacromial measures depends on the US experience of raters and on the subject status, differing between asymptomatic or patients with subacromial shoulder pain (SSP). OBJECTIVE: To evaluate inter-rater reliability between two raters with different US experience (experienced examiner and novice examiner). METHODS: In total, 20 asymptomatic subjects (controls) and 21 patients with SSP were examined on one shoulder. Inter-rater reliability was evaluated with intraclass correlation coefficient (ICC). RESULTS: ICC for controls was good for AHD at rest and at 60° (0.76-0.77), moderate for STT and AHD at 60° with weights (0.53-0.72), while OR was poorly reliable (below 0.44). ICC for SSP was moderate for AHD at rest and at 60°, STT, OR at rest and at 60° (0.52-0.74) and poor for AHD at 60° with weights and OR at 60° with weights (0.33-0.36). Bland-Altman plots showed systematic bias. CONCLUSION: Inter-rater reliability varied largely from poor to good between two examiners with different US experience. Clinicians might use the US as additional tool for detecting the subacromial structures, but a structured training including also symptomatic subjects is suggested. Researchers may further investigate the OR in matched case-control studies, and an overall agreement phase is recommended before starting the inter-rater reliability phase.