DETERMINATION OF THE PROXIMITY TOLERANCE FOR MEASUREMENT OF SURFACE-CONTACT AREAS USING A MAGNETIC TRACKING DEVICE

Undisrupted joint contact areas can be determined based on surface pro ximity from combined surface geometry and bony kinematics measured wit h a magnetic tracking device. This technique is useful for evaluating the apparent region of contact in the normal joint. After disruption o f the supporting structures or other simulated pathology, the location s and size of the contact region can be compared with the normal condi tion. However, the contact results may be highly sensitive to measurem ent errors. In this study, the accuracy of this method was evaluated f or three simple geometric objects: (1) a hat plate, (2) a cylinder, an d (3) a sphere, all in contact with a flat surface. The results indica ted the contact can be determined within an average proximity of 0.16 +/- 0.01 mm (mean +/- standard error) with the flat plate, 0.07 +/- 0. 02 mm with the cylinder, and 0.06 +/- 9.08 mm with the sphere. The pro ximity values are nearly the same as the translational accuracy of the equipment, and might be used as thresholds for in vitro studies.