Patent ID: 6928742

Claim:
A method of finding the position of a mechanical axis running in the longitudinal direction through a limb, the limb rotatably supported by a first end via a movable and inaccessible center of rotation for the mechanical determination of coordinates, comprising: providing an optical coordinate-measurement device with at least one multi-point indicator to signal measurement-point coordinates in a rotational position of the limb; rigidly attaching said multi point indicator near a second end of the limb; detecting several measurement-point coordinates (P 11 , P 21 , P 31 , P n1 ) per rotational position of the limb; recording said measurement-point coordinates; selecting from measurement-point-coordinate sets (P 11 -P n1 , P 12 -P n2 , P 1m -P nm ) at least one group; assigning said at least one group to a same site of the center of rotation; and calculating the position of the first end of the limb and a mechanical axis running through the first and second ends using the measurement-point-coordinate sets (P 11 -P n1 , P 12 -P n2 , P 1m -P nm ) assigned to said site of the center of rotation without piercing a skin of the limb above said second end.