Tracking scapular movement

Abstract

Measuring the three-dimensional movement of the scapula provides vital information in the analysis and treatment of shoulder clinical disorders and contributes to our understanding of its complex kinematics. However, the thick layer of skin overlying the scapular region means that all skin-based techniques inaccurately determine the scapular kinematics. The scapula locator makes use of a palpation technique in order to reduce the problem of skin deformation. At present, the scapula locator is the most accurate noninvasive method of measuring scapular movements, but to date the method has only been used to measure the scapula position statically. Here, a new method was developed to measure the scapula movements dynamically; the method makes use of the scapula locator and feedback from pressure-sensors attached to the locator probes to track the scapula during movement. The reliability of the method after short-term practise as well as the intra-observer and inter-observer variations and the inter-session repeatability were tested and quantified in a series of studies. The method was found to be able to measure dynamic scapular movements in slow to medium paced arm movements to a good degree of accuracy as well as provide scapulothoracic measurements of high reliability compared to using the scapula locator on its own and to previously reported results in the literature. Finally, the new locator method was used to calibrate the acromial tracker in order to improve the accuracy of the device and facilitate its use as an alternative to the scapula locator in clinical studies involving fast (higher than functional velocities) dynamic activities. The new scapula locator method and the calibrated acromial tracker method present significant improvements on the available scapular measurement techniques particularly in measuring subtle scapular rotations of clinical importance, such as the scapular tilt. The methods described will be used in future clinical and sport-related studies.