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 proximity from combined surface geometry and bony kinematics measured with a magnetic tracking device. This technique is useful for evaluating the apparent region of contact in the normal joint. After disruption of the supporting structures or other simulated pathology, the locations and size of the contact region can be compared with the normal condition. However, the contact results may be highly sensitive to measurement errors. In this study, the accuracy of this method was evaluated for three simple geometric objects: (1) a flat plate, (2) a cylinder, and (3) a sphere, all in contact with a flat surface. The results indicated 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 +/- 0.08 mm with the sphere. The proximity values are nearly the same as the translational accuracy of the equipment, and might be used as thresholds for in vitro studies.