Method and device for checking a marking element for displacement
View Patent ↗To make available a method for checking a marking element for displacement in relation to a holding structure, in particular a bone, on which this marking element is fixed, said marking element being used for determining position in navigational surgery, and said marking element functioning with the greatest possible precision, it is proposed to choose a point of orientation which is in a unique relationship to the holding structure and to monitor the position of the point of orientation in a reference system of the marking element.
1. A method for checking a marking element for displacement in relation to a holding structure, in particular a bone, on which this marking element is fixed, said marking element being used for determining position in navigational surgery, said method comprising:
choosing a point of orientation which is in a unique relationship to the holding structure, and
monitoring a position of the point of orientation in a reference system of the marking element.
2. The method of claim 1 , wherein the point of orientation is in a unique geometric relationship to the holding structure.
3. The method of claim 1 , wherein the point of orientation is an anatomical point of orientation.
4. The method of claim 1 , wherein the point of orientation is in a unique kinematic relationship to the holding structure.
5. The method of claim 1 , wherein the point of orientation is chosen by means of a pin element which has a mark whose position is invariable relative to rotation of the pin element about a pin axis, and which is fixed in a unique relationship to the holding structure.
6. The method of claim 1 , wherein the marking element comprises a screw for fixing on a bone.
7. The method of claim 6 , wherein the marking element and the screw are calibrated such that a position of a screw axis in the reference system of the marking element is known.
8. The method of claim 7 , wherein a base vector of the reference system of the marking element is offset parallel to the screw axis.
9. The method of claim 1 , wherein, in order to check the marking element for displacement, the position of the point of orientation relative to a comparison point of orientation is checked.
10. The method of claim 9 , wherein a distance between the detected point of orientation and the comparison point of orientation is determined.
11. The method of claim 9 , wherein an orthogonal distance between the detected point of orientation and the marking element is determined.
12. The method of claim 11 , wherein a warning signal is output if a difference of an orthogonal distance of the detected point of orientation and of the comparison point of orientation is different than zero.
13. The method of claim 11 , wherein a displacement angle is indicated if a difference of the orthogonal distance of the detected point of orientation and of an orthogonal distance of the comparison point is determined as zero and an angle difference in a plane perpendicular to the axis of the marking element between the detected point of orientation and the comparison point of orientation is different than zero.
14. The method of claim 9 , wherein a distance between a projection of the detected point of orientation onto an axis of the marking element and a projection of the comparison point of orientation on this axis is determined.
15. The method of claim 12 , wherein a displacement length is indicated if a difference of an orthogonal distance of the detected point of orientation and of the comparison point of orientation is determined as zero and the distance of the projections onto an axis of the marking element is different than zero.
16. The method of claim 9 , wherein an angle between the detected point of orientation and the comparison point of orientation in a plane perpendicular to an axis of the marking element is determined.
17. An apparatus for checking a marking element for displacement in relation to a holding structure, in particular a bone, on which the marking element is fixed, said marking element being used for determining position in navigational surgery, said device comprising:
a navigation device for determining the position of the marking element in space;
a device for establishing and/or determining a point of orientation which is in a unique relationship to the holding structure;
a device which determines a position of the point of orientation in a reference system of the marking element, and
a detection device for checking the marking element for displacement by checking the point of orientation for positional displacement.
18. The apparatus of claim 17 , wherein the marking element sits or is formed on a bone screw.
19. The apparatus of claim 18 , wherein the marking element and the screw are calibrated such that a position of a screw axis in the reference system of the marking element is known.
20. The apparatus of claim 17 , wherein the detection device determines at least one of:
an orthogonal distance between the detected point of orientation and the marking element;
a distance between the detected point of orientation and a comparison point of orientation;
a distance between a projection of the detected point of orientation onto the marking element and a projection of a comparison point of orientation onto the marking element, and
an angle difference between the detected point of orientation and a comparison point of orientation in a plane perpendicular to axis of the marking element.
21. The apparatus of claim 17 , wherein a pin element is used for setting the point of orientation.
22. The apparatus of claim 21 , wherein the pin element has a mark which lies coaxial to a pin axis.