Measurement of three-dimensional shoulder movement by an electromagnetic sensor

As a consequence of the difficulty in the measurement of three-dimensional motion in the clinical setting, the assessment of the shoulder joint is performed using movements about a single axis, for example, abduction, flexion and humeral rotation. The development of the Isotrak, an electromagnetic movement sensor, has made the measurement of spatial motion possible; this instrurhent has been used to measure movement at the shoulder joint. In addition to the difficulty of measurement, there is the problem of representing three-dimensional movements graphically. This paper demonstrates the inadequacy of the traditional system of clinical angles and shows that a system of spherical polar coordinates is better suited to display complex movement. Isotrak is therefore thought to be suitable for the clinical assessment of shoulder movement and this system allows for the graphical description of complex movements which have previously been difficult to define, despite the fact that it may be less easy, initially, to interpret than the traditional system.