Intra- and inter- reliability of an inertia-based motion analysis system: testing shoulder function in healthy, young adults

Abstract

Objective: To assess intra- and inter-rater reliability of an inertia-based motion analysis system (Xsens-MTw), used by untrained operators to measure range of movement at the shoulder, in order to determine whether inertial systems are a consistent objective measure for shoulder movements in physiotherapy practice. Design: Flexion, Abduction, External Rotation and Internal Rotation movements at the glenohumeral joint were measured with two sensors, strapped to the arm above the elbow and wrist. Participants: 15 asymptomatic subjects with a mean age of 23 (standard deviation 2.1) years. Results: Good reliability and low standard error was found for Abduction; both intra-rater (ICC (r)= 0.90, SEM = 4.5º) and inter-rater (r= 0.94, SEM= 3.6º). External Rotation reliability was similar with good intra-rater (r= 0.92, SEM= 12.9º) and inter-rater (r= 0.90, SEM= 13.3º), but the SEM was greater. Flexion movements had moderate reliability (r= 0.58, SEM= 7.5º for intra-rater; r= 0.61, SEM= 6.5º for inter-rater). Internal Rotation movements (measured via a movement combining more than one dimension) also had moderate reliability, intra-rater (r= 0.79, SEM= 52.8º) and inter-rater (r= 0.68, SEM= 59.2º), but the SEM was much greater for these movements. Conclusion: This inertia-based motion analysis system has moderate to high intra- and inter-rater reliability when measuring simple movements at the shoulder, but more complex movements are not as reliable between operators. Based on the findings from this study, Xsens-MTw has the potential to be used as a quantifying measure of range of movement at the shoulder in physiotherapy practice.