ACQUIRING CONTACT POSITION PARAMETERS AND DETECTING CONTACT OF A JOINT

1 . A data processing method of determining a transformation for the relative positions of two body parts which are connected to each other by a joint, the method comprising the following steps:

a) acquiring first body part position transformation data comprising first body part position transformation information describing a first body part position transformation for the position of a first body part of the two body parts relative to a first reference structure assigned to the first body part;

b) acquiring second body part position transformation data comprising second body part position transformation information describing a second body part position transformation for the position of a second other body part of the two body parts relative to a second other reference structure assigned to the second body part;

c) acquiring reference structure position transformation data comprising reference structure position transformation information describing a reference structure position transformation for the position of the first reference structure relative to the second reference structure for at least two movement states of the joint;

d) determining, based on the first body part position transformation data and the second body part position transformation data and the reference structure position transformation data, joint position transformation data comprising joint position transformation information describing a joint position transformation for the position of the first body part relative to the second body part for the at least two movement states; and

e) determining, based on the joint position transformation data, contact condition data comprising contact condition information describing whether the joint position transformation represents a position of the first and second body parts which is close or is not close to a contact position, wherein the contact position data is determined based on acquiring a data set of parameters including: a mediolateral (ml) parameter, an anterioposterior (ap) parameter, a proximodistal (pd) parameter, internal/external rotation (ie) angle parameter, a flexion angle parameter, and a varus-valgus (vv) angle parameter, wherein the data set of parameters describes the joint position transformation information, decomposing the joint position transformation based on acquiring a subset of n of the parameters that includes at least one of the ml parameter, the ap parameter, the pd parameter, and the flex parameter as an input parameter data set, wherein n is an integer in a range of one to five describing a number of predetermined parameters, determining modelled 6-n free parameters based on proximodistal modelled values and varus-valgus modelled values of the joint position transformation information and determining a model joint position transformation based on changing the joint position transformation information according to the modelled 6-n free parameters;

wherein the contact position data is determined further based on determining whether a deviation of measured values for the 6-n free parameters is within a predetermined limit from the modelled values of the modelled 6-n free parameters and on determining that the joint position transformation describes a contact position of the first and second body parts if the deviation is within the predetermined limit.

2 . The method according to claim 1 , wherein the first reference structure has a predetermined position relative to the first body part, and wherein the second reference structure has a predetermined position relative to the second body part.

3 . The method according to claim 1 , wherein step c) comprises moving first and second body parts relative to one another.

4 . The method according to claim 3 , wherein at least one of the first and second body parts is moved manually or by a driving unit.

5 . The method according to claim 1 , wherein the joint is an artificial knee joint, the first body part is the femur component of the artificial knee joint, and the second body part is the tibia component of the artificial knee joint.

6 . The method according to claim 1 , wherein determining the joint position transformation data comprises determining position parameters comprising at least one rotation parameter and at least one translation parameter between the coordinate system that is assigned to the first body part and the coordinate system that is assigned to the second body part.

7 . The method according to claim 6 , wherein the first body part and the second body part are in physical contact with one another in each of the at least two movement states and wherein contact position transformation data is determined comprising contact position transformation information.

8 . The method according to claim 7 , comprising:

acquiring position parameter grid data comprising position parameter grid information describing a grid of the position parameters for at least four degrees of freedom, wherein the nodes of the grid represent independent translations and/or independent rotations of the joint position transformation;

acquiring node assignment condition data comprising node assignment condition information describing at least one condition for the at least one determined position parameters to be fulfilled for assigning the determined at least one position parameters to a node of the grid;

determining, based on the position parameter grid data and the node assignment condition data, whether the at least one determined position parameters fulfil a condition to be assigned to the node, and if they fulfil the condition, assigning the at least one determined position parameters to that node.

9 . The method according to claim 7 , wherein if the at least one determined position parameters are assigned to a node, it is determined that the movement stage of the joint in which the position parameters were determined includes a contact position.

10 . (canceled)

11 . (canceled)

12 . The method according to claim 1 comprising outputting guidance data comprising guidance information to an operator which describes a desired direction of movement of the first and second body parts relative to one another, wherein the first body part and the second body part are in physical contact with one another in each of the at least two movement states and wherein contact position transformation data is determined comprising contact position transformation information.

13 . A computer program which, when running on a computer or when loaded onto a computer, causes the computer to digital

a) acquire first body part position transformation data comprising first body part position transformation information describing a first body part position transformation for the position of a first body part of the two body parts relative to a first reference structure assigned to the first body part;

b) acquire second body part position transformation data comprising second body part position transformation information describing a second body part position transformation for the position of a second other body part of the two body parts relative to a second other reference structure assigned to the second body part;

c) acquire reference structure position transformation data comprising reference structure position transformation information describing a reference structure position transformation for the position of the first reference structure relative to the second reference structure for at least two movement states of the joint;

d) determine, based on the first body part position transformation data and the second body part position transformation data and the reference structure position transformation data, joint position transformation data comprising joint position transformation information describing a joint position transformation for the position of the first body part relative to the second body part for the at least two movement states; and

e) determine, based on the joint position transformation data, contact condition data comprising contact condition information describing whether the joint position transformation represents a position of the first and second body parts which is close or is not close to a contact position, wherein the contact position data is determined based on acquiring a data set of parameters including: a mediolateral (ml) parameter, an anterioposterior (ap) parameter, a proximodistal (pd) parameter, internal/external rotation (ie) angle parameter, a flexion angle parameter, and a varus-valgus (vv) angle parameter, wherein the data set of parameters describes the joint position transformation information, decomposing the joint position transformation based on acquiring a subset n of the parameters that includes at least one of the ml parameter, the ap parameter, the pd parameter, and the flex parameter as an input parameter data set, wherein n is an integer in a range of one to five describing a number of predetermined parameters, determining modelled 6-n free parameters based on proximodistal modelled values and varus-valgus modelled values of the joint position transformation information and determining a model joint position transformation based on changing the joint position transformation information according to the modelled 6-n free parameters;

wherein the contact position data is determined further based on determining whether a deviation of measured values for the 6-n free parameters is within a predetermined limit from the modelled values of the modelled 6-n free parameters and on determining that the joint position transformation describes a contact position of the first and second body parts if the deviation is within the predetermined limit.

14 . A navigation system for computer-assisted surgery, comprising: a computer executing the computer program of claim 13 , for processing the first body part position transformation data, the second body part position transformation data and the reference structure position transformation data;

a detection device for detecting the position of the first and second reference structures;

a data interface for receiving data comprising information describing the position of the first and second reference structure and for supplying that data to the computer; and

a user interface for receiving data from the computer in order to provide information to a user, wherein the received data are generated by the computer on the basis of the results of the processing performed by the computer.