[Purpose] The aim of this study was to evaluate the reliability of upper quadrant posture analysis using an ultrasound-based three-dimensional motion analyzer. [Subjects] Subjects were 72 healthy young adults. [Methods] Neck inclination angle formed by a line connecting C7 and the tragus with a horizontal line, angle of the shoulder formed by a line connecting C7 and the acromial angle with a horizontal line, and cranial rotation angle formed by a line connecting the tragus and corner of the eye with a horizontal line were measured using an ultrasound-based three-dimensional motion analyzer. Intra- and inter-rater reliabilities of two testers, standard error of measurements, minimal detectable change at the 95% confidence level, and systematic bias were evaluated. [Results] Intra-class correlation coefficients (1,1) were 0.65 to 0.82. Intra-class correlation coefficients (2,1) were 0.76 to 0.82. High measurement error was found in the cranial rotation angle. Fixed bias was found for the angle of the shoulder in the inter-rater reliability. [Conclusion] Posture analysis using an ultrasound-based three-dimensional motion analyzer appears useful for assessing neck inclination angle and the angle of the shoulder in individuals, and cranial rotation angle in patient groups.
Keywords: Reliability; Systematic bias; Ultrasound-based three-dimensional motion analyzer.