Reliability of scapular kinematics estimated with three-dimensional motion analysis during shoulder elevation and flexion

BACKGROUND
Knowing the reliability of three-dimensional motion analysis to evaluate scapular kinematics during upper limb movements is essential to plan further research dedicated to understanding scapulothoracic joint movements relative to the global shoulder motion.

RESEARCH QUESTION
The aim of this study was to assess the intra-subject as well as intra- and interrater reliability of scapulothoracic joint angles during shoulder elevation in scapular plane and shoulder flexion.

METHODS
Twenty healthy participants (26.6 ± 3.5 years) were asked to perform maximum shoulder elevation in scapular plane as well as shoulder flexion. Reliability was assessed using the intraclass correlation coefficient (ICC) and its 95% confidence interval of scapular kinematics (rotation, tilting, pro-retraction) at each degree of global motion (shoulder elevation or shoulder flexion) between 0° to 150°.

RESULTS
ICCs above 0.60 were accepted as good indicators for reliability. Intra-subject reliability was found to be very high (>0.9 for most part) for all scapulothoracic joint angles during both movements. Intra- and interrater reliability also showed good reliability being above 0.60 for the most part (except scapula tilting during shoulder elevation). Scapular kinematics showed low reliability during the respective first 10° and 20° of shoulder elevation and shoulder flexion. Furthermore, decreasing reliability was found above 120° of shoulder elevation or flexion.