Precision of 3D scapular kinematic measurements for analytic arm movements and activities of daily living

Electromagnetic devices allow the non invasive and accurate measurement of 3D scapula kinematics. The acromial method allows continuous dynamic measurement using a skin surface sensor fixed to the acromion. Inter-session intra and inter-observer repeatability of 3D scapular kinematics have only been partially assessed for analytical movements and never for functional tasks. Inter-session intra and inter-observer repeatability of 3D scapular kinematics were assessed for arm elevation in the sagittal and frontal planes and for two activities of daily living (ADL), hair combing and back washing, in both shoulders of 15 healthy subjects, using the intraclass correlation coefficient (ICC), the standard error of measurement (SEM), the small real difference (SRD) and the Bland and Altman's graphical method. Intra-observer repeatability was good to excellent for every scapular rotation for both arm elevation in isolated planes and ADL (ICC ranged from 0.64 to 0.95). Inter-observer repeatability of scapular rotations was fair to excellent for arm elevation in isolated planes (ICC ranged from 0.49 to 0.92) and poor to excellent for ADL (ICC ranged from 0.35 to 0.89). Inter-observer repeatability of scapular protraction/retraction had the lowest ICC. For both inter-session intra and inter-observer reliability, the SEM and SRD remained low and Bland and Altman's graphical method showed a good repeatability of the measurement method. Longitudinal monitoring of a subject's scapular kinematics by a trained observer is reliable. The inter-observer repeatability of scapular protraction/retraction must be improved.