FACTORS INFLUENCING ACCURACY OF SCREW DISPLACEMENT AXIS DETECTION WITH A DC-BASED ELECTROMAGNETIC TRACKING SYSTEM

Recent technical improvements and cost reductions in electromagnetic m otion tracking systems invite their application to motion axis determi nation in the surgical setting. After evaluation of the accuracy of a state-of-the-art D.C. electromagnetic tracking system, which generates complete three-dimensional kinematic outputs from just a single recei ver we calculated screw displacement axes (SDA's) from its source data . The accuracy of SDA determination from such source data was evaluate d for various rotational increment sizes around a revolute joint. A no vel smoothing procedure, customized for this type of source data, was developed enabling SDA detection from incremental rotations of less th an 1 deg, at an accuracy appropriate for intra-operative measurement o f human joint motion. Examples of SDA determination are given for moti on tracking of a ball joint and of the elbow articulation.