There is described a device for use with a position sensing system to register position and orientation in a reference-coordinate system, the device comprising a set of at least three base units removably and non-invasively attachable to a skin surface covering a bone, each of the base units having a...http://www.google.fr/patents/US8152726?utm_source=gb-gplus-shareBrevet US8152726 - Non-invasive tracking of bones for surgery
