Method and device for determining the mechanical axis of a femur

• US 20040034313A1
• Filed: 06/11/2003
• Published: 02/19/2004
• Est. Priority Date: 12/15/2000
• Status: Active Grant

• Current Assignee: Aesculap AG (B. Braun Holding GmbH & Co. KG)
• Original Assignee: Aesculap AG (B. Braun Holding GmbH & Co. KG)
• Inventors: Leitner, Francois
• Granted Patent: US 7,331,932 B2
• Time in Patent Office: Days
• US Class Current: 600/595
• CPC Class Codes: A61B 17/154 for preparing bone for knee prosthesis
• CPC Class Codes: A61B 2017/00128 related to intensity or progress of surgical action
• CPC Class Codes: A61B 2034/105 Modelling of the patient, e.g. for ligaments or bones
• CPC Class Codes: A61B 2034/2055 Optical tracking systems
• CPC Class Codes: A61B 2034/2072 Reference field transducer attached to an instrument or patient
• CPC Class Codes: A61B 2090/378 using ultrasound
• CPC Class Codes: A61B 34/20 Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
• CPC Class Codes: A61B 34/25 User interfaces for surgical systems
• CPC Class Codes: A61B 5/1114 Tracking parts of the body
• CPC Class Codes: A61B 5/1121 Determining geometric values, e.g. centre of rotation or angular range of movement
• CPC Class Codes: A61B 5/1127 using markers
• CPC Class Codes: A61B 5/4504 Bones A61B5/4547 takes precedence
• CPC Class Codes: A61B 5/4528 Joints A61B5/4533, A61B5/4538 take precedence
• CPC Class Codes: A61B 90/36 Image-producing devices or illumination devices not otherwise provided for
• CPC Class Codes: G01S 15/872 Combination of several systems for attitude determination using inertial means G01C9/00, control of attitude G05D1/49
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 5/163 Determination of attitude using inertial means G01C9/00; control of attitude G05D1/49
• CPC Class Codes: G01S 5/186 Determination of attitude using inertial means G01C9/00; control of attitude G05D1/49

Abstract

In order to avoid the use of a marking element on the pelvic bone in a method for determining the mechanical axis of a femur, with which the femur is moved about the hip joint, the movement of the femur is followed via a navigation system by means of a marking element on the femur, position data of the femur obtained therefrom are stored and the position of the mechanical axis of the femur is calculated relative to the same from the various position data of the femur in various positions, it is suggested that the femur be pivoted from an initial position only through a maximum pivoting angle of 15° in various directions and that the mechanical axis of the femur be calculated from the position data of the surface area thereby covered by the marking element and from the position data of the knee joint otherwise determined. In addition, a device for carrying out this method is described.

Claims

1. Method for determining the mechanical axis of a femur, wherein the femur is moved about the hip joint, the movement of the femur is followed via a navigation system by means of a marking element on the femur, position data of the femur obtained therefrom are stored and the position of the mechanical axis of the femur is calculated relative to the same from the various position data of the femur in various positions, wherein the femur is pivoted from an initial position only through a maximum pivoting angle of 15°

in various directions and wherein the mechanical axis of the femur is calculated from the position data of the surface area thereby covered by the marking element and from the position data of the knee joint otherwise determined.

2. Method as defined in claim 1, wherein the femur is pivoted only within a maximum pivoting angle of at the most 10°

.

3. Method as defined in claim 1, wherein only position data corresponding to a pivoting angle less than a predetermined critical angle smaller than the maximum pivoting angle covered by the femur are used for the calculation of the mechanical axis.

4. Method as defined in claim 2, wherein only position data corresponding to a pivoting angle less than a predetermined critical angle smaller than the maximum pivoting angle covered by the femur are used for the calculation of the mechanical axis.

5. Method as defined in claim 3, wherein the critical angle is between 4°

and 6°

.

6. Method as defined in claim 3, wherein only position data corresponding to a pivoting angle more than a predetermined minimum angle smaller than the critical angle are used for the calculation of the mechanical axis.

7. Method as defined in claim 4, wherein only position data corresponding to a pivoting angle more than a predetermined minimum angle smaller than the critical angle are used for the calculation of the mechanical axis.

8. Method as defined in claim 6, wherein the minimum angle is more than 3°

.

9. Method as defined in claim 1, wherein all the stored position data are left out of consideration when the actual pivoting angle of the femur relative to its initial position exceeds the maximum pivoting angle.

10. Method as defined in claim 1, wherein for the calculation of the mechanical axis of the femur from the partial spherical surface covered by the marking element the center point of this partial spherical surface is calculated and the mechanical axis is determined by means of the connecting line of this center point to the knee joint.

11. Method as defined in claim 10, wherein a virtual center point of the partial spherical surface is determined first of all in that a plane is approximately calculated from the stored position data of the partial spherical surface and thereupon a vertical line extending through the knee joint and the virtual center point is assumed to be at a predetermined distance from this plane on the vertical line and wherein the mechanical axis of the femur is then calculated using the position data of the virtual center point and the position data of the partial spherical surface.

12. Method as defined in claim 11, wherein the position data of the partial spherical surface are converted to a uniform pivoting angle relative to the initial position using the position data of the virtual center point so that corrected position data defining a common circle are obtained therefrom and wherein the mid-vertical of this circle is calculated as mechanical axis of the femur.

13. Method as defined in claim 1, wherein the number and the distribution of the measured position data are determined in the entire pivoting area and the recording of additional position data is interrupted once a predetermined number and distribution are reached.

14. Method as defined in claim 1, wherein the stored position data are represented graphically in accordance with their spatial distribution in the pivoting area so that it is apparent what number of position data has been stored for which part of the possible pivoting area.

15. Method as defined in claim 14, wherein in a graphically represented surface area sections of this surface area are marked when a predetermined number of position data is recorded in a part of the pivoting area of the femur corresponding to this section.

16. Method as defined in claim 15, wherein the surface area is an annular surface area subdivided into segments.

17. Device for carrying out the method of determining the mechanical axis of a femur, comprising a navigation system for determining position data of a marking element secured on the femur and a data processing unit for calculating the position of the mechanical axis of the femur from these position data, wherein for the calculation of the position of the mechanical axis of the femur the data processing unit selects from the position data those corresponding to a pivoting angle less than a predetermined critical angle smaller than the maximum pivoting angle covered by the femur.

18. Device as defined in claim 17, wherein the critical angle is between 4°

and 6°

.

19. Device as defined in claim 17, wherein for the calculation of the position of the mechanical axis of the femur the data processing unit selects from the position data those lying above a predetermined minimum angle smaller than the critical angle.

20. Device as defined in claim 19, wherein the minimum angle is more than 3°

.

21. Device as defined in claim 17, wherein the data processing unit leaves all the stored position data out of consideration when the actual pivoting angle of the femur relative to its initial position exceeds the maximum pivoting angle.

22. Device as defined in claim 17, wherein for the calculation of the mechanical axis of the femur from the partial spherical surface covered by the marking element the data processing unit calculates the center point of this partial spherical surface and determines the mechanical axis by means of the connecting line of this center point to the knee joint.

23. Device as defined in claim 22, wherein the data processing unit determines first of all a virtual center point of the partial spherical surface in that from the stored position data of the partial spherical surface it calculates approximately a plane and thereupon a vertical line extending through the knee joint and assumes the virtual center point to be at a predetermined distance from this plane on the vertical line and wherein the data processing unit then calculates the mechanical axis of the femur using the position data of the virtual center point and the position data of the partial spherical surface.

24. Device as defined in claim 23, wherein the data processing unit converts the position data of the partial spherical surface to a uniform pivoting angle relative to the initial position using the position data of the virtual center point so that corrected position data defining a common circle are obtained therefrom and wherein it calculates the mid-vertical of this circle as mechanical axis of the femur.

25. Device as defined in claim 17, wherein the data processing unit determines the number and the distribution of the measured position data in the entire pivoting area and interrupts the recording of additional position data when a predetermined number and distribution are reached.

26. Device as defined in claim 23, wherein the data processing unit graphically represents the stored position data according to their spatial distribution in the pivoting area so that it is apparent what number of position data has been stored for which part of the possible pivoting area.

27. Device as defined in claim 26, wherein in a graphically represented surface area the data processing unit marks sections of this surface area when a predetermined number of position data has been recorded in a part of the pivoting area of the femur corresponding to this section.

28. Device as defined in claim 27, wherein the surface area is an annular surface area subdivided into segments.