Method for determining contact position parameters of a joint connecting two bones

Patent metadata

Field	Value
Publication number	US-9865095-B2
Application number	US-201214362988-A
Country	US
Kind code	B2
Filing date	Jun 20, 2012
Priority date	Dec 9, 2011
Publication date	Jan 9, 2018
Grant date	Jan 9, 2018

Abstract

A data processing method for determining six parameters, corresponding to six degrees of freedom, of a contact position of a joint which connects two bones, comprising the steps of acquiring a 3D model of each bone, acquiring four of the six parameters as given parameters, selecting initial values for the two remaining parameters and varying the two remaining parameters virtually in order to achieve a virtual relative position between the two 3D models such that they are in contact with each other.

First claim

The invention claimed is:

1. A data processing method for determining six parameters corresponding to six degrees of freedom of a contact position of a joint which connects two bones and supports a range of relative movement between the two bones, the method comprising:
acquiring a 3D model of each bone of the two bones;
acquiring four of the six parameters as fixed parameters;
selecting initial values for the two remaining parameters of the six parameters, wherein the two remaining parameters comprise a translational parameter and a rotational parameter;
varying the two remaining parameters of the six parameters from the selected initial values virtually in order to achieve a virtual relative position between the 3D models of each bone such that they are in contact with each other, wherein the 3D models of each bone are considered as being in contact with each other if the rotational parameter and the translational parameter are selected such that a minimum possible distance between the 3D models of each bone in a direction of the translational parameter is minimized; and
calculating the rotational parameter for which the minimum possible distance is minimized by:
(a) defining a range of values for the rotational parameter;
(b) calculating a first value lying in the middle of the range of values;
(c) calculating a second value lying in the middle between the lower boundary of the range of values and the first value;
(d) calculating a third value lying in the middle between the upper boundary of the range of values and the first value;
(e) determining a first minimum possible distance for the first value of the rotational parameter, a second minimum possible distance for the second value of the rotational parameter and a third minimum possible distance for the third value of the rotational parameter;
(f) repeating steps (b) to (e) for a predetermined number of iterations with a new range of values, the new range of values having half the width of the current range of values and being centered about the one of the first, second or third values which results in the smallest of the first, second and third minimum possible distances; and
(g) selecting the one of the first, second or third values which results in the smallest of the first, second and third minimum possible distance for the rotational parameter.

2. The method of claim 1 , further comprising selecting the initial values for the remaining parameters such that the 3D models of each bone are not in contact with each other.

3. The method according to claim 1 , wherein an axis of rotation of the rotational parameter is perpendicular to a direction of the translational parameter.

4. The method according to claim 1 , wherein:
the 3D models of each bone are moved virtually towards each other along a direction of the translational parameter until there is a first contact point between surfaces of the two 3D models;
the virtual movement is continued until there is a second contact point between the surfaces of the 3D models; and
the rotational parameter is then calculated such that the two 3D models of the two bones are in contact at two contact points.

5. The method according to claim 4 , wherein:
the rotational parameter is changed such that a difference of distances by which the first contact point and the second contact point are moved in the direction of the translational parameter by changing the rotational parameter equals the distance by which the 3D models are moved virtually towards each other in the direction of the translational parameter between reaching the first contact point and the second contact point, and
the translational parameter is amended such that the movement of the second contact point in the direction of the translational parameter, caused by the rotation about the rotational parameter, is compensated.

6. The method according to claim 4 , wherein the varying the two remaining parameters is repeated in a further iteration, with the value which was determined in the preceding iteration being selected as the initial value of the rotational parameter.

7. The method according to claim 1 , wherein when the 3D models of each bone touch over an area and not at a single contact point, the center of this area is chosen as a contact point.

8. The method of claim 1 , further comprising defining a plurality of parameter sets for the four fixed parameters, and determining a contact position for each of the parameter sets.

9. The method according to claim 8 , further comprising varying each fixed parameter in the parameter sets in steps within a given range.

10. The method according to claim 1 , further comprising using collision detection techniques to determine whether there is a contact between the surfaces of the 3D models of each bone.

11. The method according to claim 1 , wherein the acquiring the four of the six parameters comprises four of:
acquiring a parameter defining a translational shift in a proximodistal (pd) direction between the first and second bones;
acquiring a parameter defining a translational shift in a anterioposterior (ap) direction between the first and second bones;
acquiring a parameter defining a translational shift in a mediolateral (ml) direction between the first and second bones;
acquiring a parameter defining a rotational shift in a flexion/extension (fe) angle between the first and second bones;
acquiring a parameter defining a rotational shift in an internal/external (ie) angle between the first and second bones; and
acquiring a parameter defining a rotational shift in a varus/valgus (vv) angle between the first and second bones.

12. The method according to claim 11 , wherein:
the acquiring the four of the six parameters comprises:
acquiring the parameter defining the translational shift in the anterioposterior (ap) direction between the first and second bones;
acquiring the parameter defining the translational shift in the mediolateral (ml) direction between the first and second bones;
acquiring the parameter defining the rotational shift in the flexion/extension (fe) angle between the first and second bones; and
acquiring the parameter defining the rotational shift in the internal/external (ie) angle between the first and second bones; and

the varying the two remaining parameters comprises virtually varying the parameter defining the translational shift in the proximodistal (pd) direction between the first and second bones and virtually varying the parameter defining the rotational shift in the varus/valgus (vv) angle between the first and second bones in order to achieve the virtual relative position between the 3D models of each bone such that they are in contact with each other.

13. A non-transitory computer readable storage medium comprising a computer program which, when running on a computer or when loaded onto a computer, causes the computer to perform a data processing method for determining six parameters corresponding to six degrees of freedom of a contact position of a joint which connects two bones and supports a range of relative movement between the two bones, the method comprising:
acquiring a 3D model of each bone of the two bones;
acquiring four of the six parameters as fixed parameters;
selecting initial values for the two remaining parameters of the six parameters, wherein the two remaining parameters comprise a translational parameter and a rotational parameter;
varying the two remaining parameters of the six parameters from the selected initial values virtually in order to achieve a virtual relative position between the 3D models of each bone such that they are in contact with each other, wherein

Assignees

• Gotte Hubert
• Dohmen Lars
• Brainlab Ag

Inventors

• Gotte Hubert
• Dohmen Lars

Classifications

• A61B5/4585

  Evaluating the knee · CPC title

• G16H50/50

  for simulation or modelling of medical disorders · CPC title

• A61B2034/105

  Modelling of the patient, e.g. for ligaments or bones · CPC title

• A61B34/10

  Computer-aided planning, simulation or modelling of surgical operations · CPC title

• A61B5/11

  Measuring movement of the entire body or parts thereof, e.g. head or hand tremor or mobility of a limb {(A61B5/1038 takes precedence; motion detection to correct for motion artifacts in physiological signals A61B5/721)} · CPC title