Comparison of changes in supraspinatus muscle thickness in persons with subacromial impingement syndrome and asymptomatic adults

PURPOSE: To compare changes in supraspinatus muscle thickness in persons with subacromial impingement syndrome (SAIS) and asymptomatic adults and to determine the reliability of the ultrasound imaging (USI) protocol. SUBJECTS: Twenty-two persons with SAIS and 22 age- and gender-matched asymptomatic controls. METHODS: Ultrasound images of supraspinatus muscle thickness at rest and at 0°, 30°, 60°, and 90° of arm elevation were captured and measured. To determine same-day intratester reliability, one examiner imaged the same subject twice and two examiners took turns capturing images in order to determine same-day intertester reliability. SUBJECTS were asked to return for between-day intratester reliability. RESULTS: Statistical analyses revealed a larger mean supraspinatus thickness in the SAIS group at the 0° condition than in the asymptomatic group (p < 0.05). Same-day intratester and intertester reliability was good with ICC(2,3) = 0.73-0.96 for asymptomatic controls and ICC(2,3) = 0.61-0.94 for persons with SAIS. Overall, between-day intratester reliability was fair to good for most conditions [ICC(2,3) = 0.31-0.90]. CONCLUSIONS: The thicker supraspinatus muscles at 0° in the SAIS group may indicate a protective spasm. The USI protocol used in the study demonstrated good same-day intratester and intertester reliability for both groups.